|
HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
VALGRIND(1) valgrind VALGRIND(1)
valgrind - a suite of tools for debugging and profiling programs
valgrind [valgrind-options] [your-program] [your-program-options]
Valgrind is a flexible program for debugging and profiling Linux
executables. It consists of a core, which provides a synthetic CPU
in software, and a series of debugging and profiling tools. The
architecture is modular, so that new tools can be created easily
and without disturbing the existing structure.
Some of the options described below work with all Valgrind tools,
and some only work with a few or one. The section MEMCHECK OPTIONS
and those below it describe tool-specific options.
This manual page covers only basic usage and options. For more
comprehensive information, please see the HTML documentation on
your system: $INSTALL/share/doc/valgrind/html/index.html, or
online: http://www.valgrind.org/docs/manual/index.html.
The single most important option.
--tool=<toolname> [default: memcheck]
Run the Valgrind tool called toolname, e.g. memcheck,
cachegrind, callgrind, helgrind, drd, massif, dhat, lackey,
none, exp-bbv, etc.
These options work with all tools.
-h --help
Show help for all options, both for the core and for the
selected tool. If the option is repeated it is equivalent to
giving --help-debug.
--help-debug
Same as --help, but also lists debugging options which usually
are only of use to Valgrind's developers.
--version
Show the version number of the Valgrind core. Tools can have
their own version numbers. There is a scheme in place to
ensure that tools only execute when the core version is one
they are known to work with. This was done to minimise the
chances of strange problems arising from tool-vs-core version
incompatibilities.
-q, --quiet
Run silently, and only print error messages. Useful if you are
running regression tests or have some other automated test
machinery.
-v, --verbose
Be more verbose. Gives extra information on various aspects of
your program, such as: the shared objects loaded, the
suppressions used, the progress of the instrumentation and
execution engines, and warnings about unusual behaviour.
Repeating the option increases the verbosity level.
--trace-children=<yes|no> [default: no]
When enabled, Valgrind will trace into sub-processes initiated
via the exec system call. This is necessary for multi-process
programs.
Note that Valgrind does trace into the child of a fork (it
would be difficult not to, since fork makes an identical copy
of a process), so this option is arguably badly named.
However, most children of fork calls immediately call exec
anyway.
--trace-children-skip=patt1,patt2,...
This option only has an effect when --trace-children=yes is
specified. It allows for some children to be skipped. The
option takes a comma separated list of patterns for the names
of child executables that Valgrind should not trace into.
Patterns may include the metacharacters ? and *, which have
the usual meaning.
This can be useful for pruning uninteresting branches from a
tree of processes being run on Valgrind. But you should be
careful when using it. When Valgrind skips tracing into an
executable, it doesn't just skip tracing that executable, it
also skips tracing any of that executable's child processes.
In other words, the flag doesn't merely cause tracing to stop
at the specified executables -- it skips tracing of entire
process subtrees rooted at any of the specified executables.
--trace-children-skip-by-arg=patt1,patt2,...
This is the same as --trace-children-skip, with one
difference: the decision as to whether to trace into a child
process is made by examining the arguments to the child
process, rather than the name of its executable.
--child-silent-after-fork=<yes|no> [default: no]
When enabled, Valgrind will not show any debugging or logging
output for the child process resulting from a fork call. This
can make the output less confusing (although more misleading)
when dealing with processes that create children. It is
particularly useful in conjunction with --trace-children=. Use
of this option is also strongly recommended if you are
requesting XML output (--xml=yes), since otherwise the XML
from child and parent may become mixed up, which usually makes
it useless.
--vgdb=<no|yes|full> [default: yes]
Valgrind will provide "gdbserver" functionality when
--vgdb=yes or --vgdb=full is specified. This allows an
external GNU GDB debugger to control and debug your program
when it runs on Valgrind. --vgdb=full incurs significant
performance overheads, but provides more precise breakpoints
and watchpoints. See Debugging your program using Valgrind's
gdbserver and GDB for a detailed description.
If the embedded gdbserver is enabled but no gdb is currently
being used, the vgdb command line utility can send "monitor
commands" to Valgrind from a shell. The Valgrind core provides
a set of Valgrind monitor commands. A tool can optionally
provide tool specific monitor commands, which are documented
in the tool specific chapter.
--vgdb-error=<number> [default: 999999999]
Use this option when the Valgrind gdbserver is enabled with
--vgdb=yes or --vgdb=full. Tools that report errors will wait
for "number" errors to be reported before freezing the program
and waiting for you to connect with GDB. It follows that a
value of zero will cause the gdbserver to be started before
your program is executed. This is typically used to insert GDB
breakpoints before execution, and also works with tools that
do not report errors, such as Massif.
--vgdb-stop-at=<set> [default: none]
Use this option when the Valgrind gdbserver is enabled with
--vgdb=yes or --vgdb=full. The Valgrind gdbserver will be
invoked for each error after --vgdb-error have been reported.
You can additionally ask the Valgrind gdbserver to be invoked
for other events, specified in one of the following ways:
• a comma separated list of one or more of startup exit
abexit valgrindabexit.
The values startup exit valgrindabexit respectively
indicate to invoke gdbserver before your program is
executed, after the last instruction of your program, on
Valgrind abnormal exit (e.g. internal error, out of
memory, ...).
The option abexit is similar to exit but tells to invoke
gdbserver only when your application exits abnormally
(i.e. with an exit code different of 0).
Note: startup and --vgdb-error=0 will both cause Valgrind
gdbserver to be invoked before your program is executed.
The --vgdb-error=0 will in addition cause your program to
stop on all subsequent errors.
• all to specify the complete set. It is equivalent to
--vgdb-stop-at=startup,exit,abexit,valgrindabexit.
• none for the empty set.
--track-fds=<yes|no|all> [default: no]
When enabled, Valgrind will print out a list of open file
descriptors on exit or on request, via the gdbserver monitor
command v.info open_fds. Along with each file descriptor is
printed a stack backtrace of where the file was opened and any
details relating to the file descriptor such as the file name
or socket details. Use all to include reporting on stdin,
stdout and stderr.
--time-stamp=<yes|no> [default: no]
When enabled, each message is preceded with an indication of
the elapsed wallclock time since startup, expressed as days,
hours, minutes, seconds and milliseconds.
--log-fd=<number> [default: 2, stderr]
Specifies that Valgrind should send all of its messages to the
specified file descriptor. The default, 2, is the standard
error channel (stderr). Note that this may interfere with the
client's own use of stderr, as Valgrind's output will be
interleaved with any output that the client sends to stderr.
--log-file=<filename>
Specifies that Valgrind should send all of its messages to the
specified file. If the file name is empty, it causes an abort.
There are three special format specifiers that can be used in
the file name.
%p is replaced with the current process ID. This is very
useful for program that invoke multiple processes. WARNING: If
you use --trace-children=yes and your program invokes multiple
processes OR your program forks without calling exec
afterwards, and you don't use this specifier (or the %q
specifier below), the Valgrind output from all those processes
will go into one file, possibly jumbled up, and possibly
incomplete. Note: If the program forks and calls exec
afterwards, Valgrind output of the child from the period
between fork and exec will be lost. Fortunately this gap is
really tiny for most programs; and modern programs use
posix_spawn anyway.
%n is replaced with a file sequence number unique for this
process. This is useful for processes that produces several
files from the same filename template.
%q{FOO} is replaced with the contents of the environment
variable FOO. If the {FOO} part is malformed, it causes an
abort. This specifier is rarely needed, but very useful in
certain circumstances (eg. when running MPI programs). The
idea is that you specify a variable which will be set
differently for each process in the job, for example
BPROC_RANK or whatever is applicable in your MPI setup. If the
named environment variable is not set, it causes an abort.
Note that in some shells, the { and } characters may need to
be escaped with a backslash.
%% is replaced with %.
If an % is followed by any other character, it causes an
abort.
If the file name specifies a relative file name, it is put in
the program's initial working directory: this is the current
directory when the program started its execution after the
fork or after the exec. If it specifies an absolute file name
(ie. starts with '/') then it is put there.
--log-socket=<ip-address:port-number>
Specifies that Valgrind should send all of its messages to the
specified port at the specified IP address. The port may be
omitted, in which case port 1500 is used. If a connection
cannot be made to the specified socket, Valgrind falls back to
writing output to the standard error (stderr). This option is
intended to be used in conjunction with the valgrind-listener
program. For further details, see the commentary in the
manual.
--enable-debuginfod=<no|yes> [default: yes]
When enabled Valgrind will attempt to download missing
debuginfo from debuginfod servers if space-separated server
URLs are present in the $DEBUGINFOD_URLS environment variable.
This option is supported on Linux only.
These options are used by all tools that can report errors, e.g.
Memcheck, but not Cachegrind.
--xml=<yes|no> [default: no]
When enabled, the important parts of the output (e.g. tool
error messages) will be in XML format rather than plain text.
Furthermore, the XML output will be sent to a different output
channel than the plain text output. Therefore, you also must
use one of --xml-fd, --xml-file or --xml-socket to specify
where the XML is to be sent.
Less important messages will still be printed in plain text,
but because the XML output and plain text output are sent to
different output channels (the destination of the plain text
output is still controlled by --log-fd, --log-file and
--log-socket) this should not cause problems.
This option is aimed at making life easier for tools that
consume Valgrind's output as input, such as GUI front ends.
Currently this option works with Memcheck, Helgrind and DRD.
The output format is specified in the file
docs/internals/xml-output-protocol4.txt in the source tree for
Valgrind 3.5.0 or later.
The recommended options for a GUI to pass, when requesting XML
output, are: --xml=yes to enable XML output, --xml-file to
send the XML output to a (presumably GUI-selected) file,
--log-file to send the plain text output to a second
GUI-selected file, --child-silent-after-fork=yes, and -q to
restrict the plain text output to critical error messages
created by Valgrind itself. For example, failure to read a
specified suppressions file counts as a critical error
message. In this way, for a successful run the text output
file will be empty. But if it isn't empty, then it will
contain important information which the GUI user should be
made aware of.
--xml-fd=<number> [default: -1, disabled]
Specifies that Valgrind should send its XML output to the
specified file descriptor. It must be used in conjunction with
--xml=yes.
--xml-file=<filename>
Specifies that Valgrind should send its XML output to the
specified file. It must be used in conjunction with --xml=yes.
Any %p or %q sequences appearing in the filename are expanded
in exactly the same way as they are for --log-file. See the
description of --log-file for details.
--xml-socket=<ip-address:port-number>
Specifies that Valgrind should send its XML output the
specified port at the specified IP address. It must be used in
conjunction with --xml=yes. The form of the argument is the
same as that used by --log-socket. See the description of
--log-socket for further details.
--xml-user-comment=<string>
Embeds an extra user comment string at the start of the XML
output. Only works when --xml=yes is specified; ignored
otherwise.
--demangle=<yes|no> [default: yes]
Enable/disable automatic demangling (decoding) of C++, D,
Rust, Java, Ada names. Enabled by default. When enabled,
Valgrind will attempt to translate encoded names in the listed
languages back to something approaching the original. Note
that the callgrind tool always disables Ada demangling in
order to differentiate overloaded functions and procedures in
the callgraph. The demangler handles symbols mangled by g++
versions 2.X, 3.X and 4.X.
An important fact about demangling is that function names
mentioned in suppressions files should be in their mangled
form. Valgrind does not demangle function names when searching
for applicable suppressions, because to do otherwise would
make suppression file contents dependent on the state of
Valgrind's demangling machinery, and also slow down
suppression matching.
--num-callers=<number> [default: 12]
Specifies the maximum number of entries shown in stack traces
that identify program locations. Note that errors are commoned
up using only the top four function locations (the place in
the current function, and that of its three immediate
callers). So this doesn't affect the total number of errors
reported.
The maximum value for this is 500. Note that higher settings
will make Valgrind run a bit more slowly and take a bit more
memory, but can be useful when working with programs with
deeply-nested call chains.
--unw-stack-scan-thresh=<number> [default: 0] ,
--unw-stack-scan-frames=<number> [default: 5]
Stack-scanning support is available only on ARM targets.
These flags enable and control stack unwinding by stack
scanning. When the normal stack unwinding mechanisms -- usage
of Dwarf CFI records, and frame-pointer following -- fail,
stack scanning may be able to recover a stack trace.
Note that stack scanning is an imprecise, heuristic mechanism
that may give very misleading results, or none at all. It
should be used only in emergencies, when normal unwinding
fails, and it is important to nevertheless have stack traces.
Stack scanning is a simple technique: the unwinder reads words
from the stack, and tries to guess which of them might be
return addresses, by checking to see if they point just after
ARM or Thumb call instructions. If so, the word is added to
the backtrace.
The main danger occurs when a function call returns, leaving
its return address exposed, and a new function is called, but
the new function does not overwrite the old address. The
result of this is that the backtrace may contain entries for
functions which have already returned, and so be very
confusing.
A second limitation of this implementation is that it will
scan only the page (4KB, normally) containing the starting
stack pointer. If the stack frames are large, this may result
in only a few (or not even any) being present in the trace.
Also, if you are unlucky and have an initial stack pointer
near the end of its containing page, the scan may miss all
interesting frames.
By default stack scanning is disabled. The normal use case is
to ask for it when a stack trace would otherwise be very
short. So, to enable it, use --unw-stack-scan-thresh=number.
This requests Valgrind to try using stack scanning to "extend"
stack traces which contain fewer than number frames.
If stack scanning does take place, it will only generate at
most the number of frames specified by
--unw-stack-scan-frames. Typically, stack scanning generates
so many garbage entries that this value is set to a low value
(5) by default. In no case will a stack trace larger than the
value specified by --num-callers be created.
--error-limit=<yes|no> [default: yes]
When enabled, Valgrind stops reporting errors after 10,000,000
in total, or 1,000 different ones, have been seen. This is to
stop the error tracking machinery from becoming a huge
performance overhead in programs with many errors.
--error-exitcode=<number> [default: 0]
Specifies an alternative exit code to return if Valgrind
reported any errors in the run. When set to the default value
(zero), the return value from Valgrind will always be the
return value of the process being simulated. When set to a
nonzero value, that value is returned instead, if Valgrind
detects any errors. This is useful for using Valgrind as part
of an automated test suite, since it makes it easy to detect
test cases for which Valgrind has reported errors, just by
inspecting return codes. When set to a nonzero value and
Valgrind detects no error, the return value of Valgrind will
be the return value of the program being simulated.
--exit-on-first-error=<yes|no> [default: no]
If this option is enabled, Valgrind exits on the first error.
A nonzero exit value must be defined using --error-exitcode
option. Useful if you are running regression tests or have
some other automated test machinery.
--error-markers=<begin>,<end> [default: none]
When errors are output as plain text (i.e. XML not used),
--error-markers instructs to output a line containing the
begin (end) string before (after) each error.
Such marker lines facilitate searching for errors and/or
extracting errors in an output file that contain valgrind
errors mixed with the program output.
Note that empty markers are accepted. So, only using a begin
(or an end) marker is possible.
--show-error-list=no|yes|all [default: no]
If this option is yes, for tools that report errors, valgrind
will show the list of detected errors and the list of used
suppressions at exit. The value all indicates to also show the
list of suppressed errors.
Note that at verbosity 2 and above, valgrind automatically
shows the list of detected errors and the list of used
suppressions at exit, unless --show-error-list=no is selected.
-s
Specifying -s is equivalent to --show-error-list=yes.
--sigill-diagnostics=<yes|no> [default: yes]
Enable/disable printing of illegal instruction diagnostics.
Enabled by default, but defaults to disabled when --quiet is
given. The default can always be explicitly overridden by
giving this option.
When enabled, a warning message will be printed, along with
some diagnostics, whenever an instruction is encountered that
Valgrind cannot decode or translate, before the program is
given a SIGILL signal. Often an illegal instruction indicates
a bug in the program or missing support for the particular
instruction in Valgrind. But some programs do deliberately try
to execute an instruction that might be missing and trap the
SIGILL signal to detect processor features. Using this flag
makes it possible to avoid the diagnostic output that you
would otherwise get in such cases.
--keep-debuginfo=<yes|no> [default: no]
When enabled, keep ("archive") symbols and all other debuginfo
for unloaded code. This allows saved stack traces to include
file/line info for code that has been dlclose'd (or similar).
Be careful with this, since it can lead to unbounded memory
use for programs which repeatedly load and unload shared
objects.
Some tools and some functionalities have only limited support
for archived debug info. Memcheck fully supports it.
Generally, tools that report errors can use archived debug
info to show the error stack traces. The known limitations
are: Helgrind's past access stack trace of a race condition is
does not use archived debug info. Massif (and more generally
the xtree Massif output format) does not make use of archived
debug info. Only Memcheck has been (somewhat) tested with
--keep-debuginfo=yes, so other tools may have unknown
limitations.
--show-below-main=<yes|no> [default: no]
By default, stack traces for errors do not show any functions
that appear beneath main because most of the time it's
uninteresting C library stuff and/or gobbledygook.
Alternatively, if main is not present in the stack trace,
stack traces will not show any functions below main-like
functions such as glibc's __libc_start_main. Furthermore, if
main-like functions are present in the trace, they are
normalised as (below main), in order to make the output more
deterministic.
If this option is enabled, all stack trace entries will be
shown and main-like functions will not be normalised.
--fullpath-after=<string> [default: don't show source paths]
By default Valgrind only shows the filenames in stack traces,
but not full paths to source files. When using Valgrind in
large projects where the sources reside in multiple different
directories, this can be inconvenient. --fullpath-after
provides a flexible solution to this problem. When this option
is present, the path to each source file is shown, with the
following all-important caveat: if string is found in the
path, then the path up to and including string is omitted,
else the path is shown unmodified. Note that string is not
required to be a prefix of the path.
For example, consider a file named
/home/janedoe/blah/src/foo/bar/xyzzy.c. Specifying
--fullpath-after=/home/janedoe/blah/src/ will cause Valgrind
to show the name as foo/bar/xyzzy.c.
Because the string is not required to be a prefix,
--fullpath-after=src/ will produce the same output. This is
useful when the path contains arbitrary machine-generated
characters. For example, the path
/my/build/dir/C32A1B47/blah/src/foo/xyzzy can be pruned to
foo/xyzzy using --fullpath-after=/blah/src/.
If you simply want to see the full path, just specify an empty
string: --fullpath-after=. This isn't a special case, merely a
logical consequence of the above rules.
Finally, you can use --fullpath-after multiple times. Any
appearance of it causes Valgrind to switch to producing full
paths and applying the above filtering rule. Each produced
path is compared against all the --fullpath-after-specified
strings, in the order specified. The first string to match
causes the path to be truncated as described above. If none
match, the full path is shown. This facilitates chopping off
prefixes when the sources are drawn from a number of unrelated
directories.
--extra-debuginfo-path=<path> [default: undefined and unused]
By default Valgrind searches in several well-known paths for
debug objects, such as /usr/lib/debug/.
However, there may be scenarios where you may wish to put
debug objects at an arbitrary location, such as external
storage when running Valgrind on a mobile device with limited
local storage. Another example might be a situation where you
do not have permission to install debug object packages on the
system where you are running Valgrind.
In these scenarios, you may provide an absolute path as an
extra, final place for Valgrind to search for debug objects by
specifying --extra-debuginfo-path=/path/to/debug/objects. The
given path will be prepended to the absolute path name of the
searched-for object. For example, if Valgrind is looking for
the debuginfo for /w/x/y/zz.so and
--extra-debuginfo-path=/a/b/c is specified, it will look for a
debug object at /a/b/c/w/x/y/zz.so.
This flag should only be specified once. If it is specified
multiple times, only the last instance is honoured.
--debuginfo-server=ipaddr:port [default: undefined and unused]
This is a new, experimental, feature introduced in version
3.9.0.
In some scenarios it may be convenient to read debuginfo from
objects stored on a different machine. With this flag,
Valgrind will query a debuginfo server running on ipaddr and
listening on port port, if it cannot find the debuginfo object
in the local filesystem.
The debuginfo server must accept TCP connections on port port.
The debuginfo server is contained in the source file
auxprogs/valgrind-di-server.c. It will only serve from the
directory it is started in. port defaults to 1500 in both
client and server if not specified.
If Valgrind looks for the debuginfo for /w/x/y/zz.so by using
the debuginfo server, it will strip the pathname components
and merely request zz.so on the server. That in turn will look
only in its current working directory for a matching debuginfo
object.
The debuginfo data is transmitted in small fragments (8 KB) as
requested by Valgrind. Each block is compressed using LZO to
reduce transmission time. The implementation has been tuned
for best performance over a single-stage 802.11g (WiFi)
network link.
Note that checks for matching primary vs debug objects, using
GNU debuglink CRC scheme, are performed even when using the
debuginfo server. To disable such checking, you need to also
specify --allow-mismatched-debuginfo=yes.
By default the Valgrind build system will build
valgrind-di-server for the target platform, which is almost
certainly not what you want. So far we have been unable to
find out how to get automake/autoconf to build it for the
build platform. If you want to use it, you will have to
recompile it by hand using the command shown at the top of
auxprogs/valgrind-di-server.c.
Valgrind can also download debuginfo via debuginfod. See the
DEBUGINFOD section for more information.
--allow-mismatched-debuginfo=no|yes [no]
When reading debuginfo from separate debuginfo objects,
Valgrind will by default check that the main and debuginfo
objects match, using the GNU debuglink mechanism. This
guarantees that it does not read debuginfo from out of date
debuginfo objects, and also ensures that Valgrind can't crash
as a result of mismatches.
This check can be overridden using
--allow-mismatched-debuginfo=yes. This may be useful when the
debuginfo and main objects have not been split in the proper
way. Be careful when using this, though: it disables all
consistency checking, and Valgrind has been observed to crash
when the main and debuginfo objects don't match.
--suppressions=<filename> [default:
$PREFIX/lib/valgrind/default.supp]
Specifies an extra file from which to read descriptions of
errors to suppress. You may use up to 100 extra suppression
files.
--gen-suppressions=<yes|no|all> [default: no]
When set to yes, Valgrind will pause after every error shown
and print the line:
---- Print suppression ? --- [Return/N/n/Y/y/C/c] ----
Pressing Ret, or N Ret or n Ret, causes Valgrind continue
execution without printing a suppression for this error.
Pressing Y Ret or y Ret causes Valgrind to write a suppression
for this error. You can then cut and paste it into a
suppression file if you don't want to hear about the error in
the future.
When set to all, Valgrind will print a suppression for every
reported error, without querying the user.
This option is particularly useful with C++ programs, as it
prints out the suppressions with mangled names, as required.
Note that the suppressions printed are as specific as
possible. You may want to common up similar ones, by adding
wildcards to function names, and by using frame-level
wildcards. The wildcarding facilities are powerful yet
flexible, and with a bit of careful editing, you may be able
to suppress a whole family of related errors with only a few
suppressions.
Sometimes two different errors are suppressed by the same
suppression, in which case Valgrind will output the
suppression more than once, but you only need to have one copy
in your suppression file (but having more than one won't cause
problems). Also, the suppression name is given as <insert a
suppression name here>; the name doesn't really matter, it's
only used with the -v option which prints out all used
suppression records.
--input-fd=<number> [default: 0, stdin]
When using --gen-suppressions=yes, Valgrind will stop so as to
read keyboard input from you when each error occurs. By
default it reads from the standard input (stdin), which is
problematic for programs which close stdin. This option allows
you to specify an alternative file descriptor from which to
read input.
--dsymutil=no|yes [yes]
This option is only relevant when running Valgrind on macOS.
macOS uses a deferred debug information (debuginfo) linking
scheme. When object files containing debuginfo are linked into
a .dylib or an executable, the debuginfo is not copied into
the final file. Instead, the debuginfo must be linked manually
by running dsymutil, a system-provided utility, on the
executable or .dylib. The resulting combined debuginfo is
placed in a directory alongside the executable or .dylib, but
with the extension .dSYM.
With --dsymutil=no, Valgrind will detect cases where the .dSYM
directory is either missing, or is present but does not appear
to match the associated executable or .dylib, most likely
because it is out of date. In these cases, Valgrind will print
a warning message but take no further action.
With --dsymutil=yes, Valgrind will, in such cases,
automatically run dsymutil as necessary to bring the debuginfo
up to date. For all practical purposes, if you always use
--dsymutil=yes, then there is never any need to run dsymutil
manually or as part of your applications's build system, since
Valgrind will run it as necessary.
Valgrind will not attempt to run dsymutil on any executable or
library in /usr/, /bin/, /sbin/, /opt/, /sw/, /System/,
/Library/ or /Applications/ since dsymutil will always fail in
such situations. It fails both because the debuginfo for such
pre-installed system components is not available anywhere, and
also because it would require write privileges in those
directories.
Be careful when using --dsymutil=yes, since it will cause
pre-existing .dSYM directories to be silently deleted and
re-created. Also note that dsymutil is quite slow, sometimes
excessively so.
--max-stackframe=<number> [default: 2000000]
The maximum size of a stack frame. If the stack pointer moves
by more than this amount then Valgrind will assume that the
program is switching to a different stack.
You may need to use this option if your program has large
stack-allocated arrays. Valgrind keeps track of your program's
stack pointer. If it changes by more than the threshold
amount, Valgrind assumes your program is switching to a
different stack, and Memcheck behaves differently than it
would for a stack pointer change smaller than the threshold.
Usually this heuristic works well. However, if your program
allocates large structures on the stack, this heuristic will
be fooled, and Memcheck will subsequently report large numbers
of invalid stack accesses. This option allows you to change
the threshold to a different value.
You should only consider use of this option if Valgrind's
debug output directs you to do so. In that case it will tell
you the new threshold you should specify.
In general, allocating large structures on the stack is a bad
idea, because you can easily run out of stack space,
especially on systems with limited memory or which expect to
support large numbers of threads each with a small stack, and
also because the error checking performed by Memcheck is more
effective for heap-allocated data than for stack-allocated
data. If you have to use this option, you may wish to consider
rewriting your code to allocate on the heap rather than on the
stack.
--main-stacksize=<number> [default: use current 'ulimit' value]
Specifies the size of the main thread's stack.
To simplify its memory management, Valgrind reserves all
required space for the main thread's stack at startup. That
means it needs to know the required stack size at startup.
By default, Valgrind uses the current "ulimit" value for the
stack size, or 16 MB, whichever is lower. In many cases this
gives a stack size in the range 8 to 16 MB, which almost never
overflows for most applications.
If you need a larger total stack size, use --main-stacksize to
specify it. Only set it as high as you need, since reserving
far more space than you need (that is, hundreds of megabytes
more than you need) constrains Valgrind's memory allocators
and may reduce the total amount of memory that Valgrind can
use. This is only really of significance on 32-bit machines.
On Linux, you may request a stack of size up to 2GB. Valgrind
will stop with a diagnostic message if the stack cannot be
allocated.
--main-stacksize only affects the stack size for the program's
initial thread. It has no bearing on the size of thread
stacks, as Valgrind does not allocate those.
You may need to use both --main-stacksize and --max-stackframe
together. It is important to understand that --main-stacksize
sets the maximum total stack size, whilst --max-stackframe
specifies the largest size of any one stack frame. You will
have to work out the --main-stacksize value for yourself
(usually, if your applications segfaults). But Valgrind will
tell you the needed --max-stackframe size, if necessary.
As discussed further in the description of --max-stackframe, a
requirement for a large stack is a sign of potential
portability problems. You are best advised to place all large
data in heap-allocated memory.
--max-threads=<number> [default: 500]
By default, Valgrind can handle to up to 500 threads.
Occasionally, that number is too small. Use this option to
provide a different limit. E.g. --max-threads=3000.
--realloc-zero-bytes-frees=yes|no [default: yes for glibc no
otherwise]
The behaviour of realloc() with a size of zero is
implementation defined in C17 and undefined in C23. Valgrind
tries to work in the same way as the underlying system and C
runtime library that it was configured and built on. However,
if you use a different C runtime library then this default may
be wrong. If the value is yes then realloc will deallocate the
memory and return NULL. If the value is no then realloc will
not deallocate the memory and the size will be handled as
though it were one byte.
As an example, if you use Valgrind installed via a package on
a Linux distro using GNU libc but link your test executable
with musl libc or the JEMalloc library then consider using
--realloc-zero-bytes-frees=no.
Address Sanitizer has a similar and even wordier option
allocator_frees_and_returns_null_on_realloc_zero.
For tools that use their own version of malloc (e.g. Memcheck,
Massif, Helgrind, DRD), the following options apply.
--alignment=<number> [default: 8 or 16, depending on the platform]
By default Valgrind's malloc, realloc, etc, return a block
whose starting address is 8-byte aligned or 16-byte aligned
(the value depends on the platform and matches the platform
default). This option allows you to specify a different
alignment. The supplied value must be greater than or equal to
the default, less than or equal to 4096, and must be a power
of two.
--redzone-size=<number> [default: depends on the tool]
Valgrind's malloc, realloc, etc, add padding blocks before and
after each heap block allocated by the program being run. Such
padding blocks are called redzones. The default value for the
redzone size depends on the tool. For example, Memcheck adds
and protects a minimum of 16 bytes before and after each block
allocated by the client. This allows it to detect block
underruns or overruns of up to 16 bytes.
Increasing the redzone size makes it possible to detect
overruns of larger distances, but increases the amount of
memory used by Valgrind. Decreasing the redzone size will
reduce the memory needed by Valgrind but also reduces the
chances of detecting over/underruns, so is not recommended.
--xtree-memory=none|allocs|full [none]
Tools replacing Valgrind's malloc, realloc, etc, can
optionally produce an execution tree detailing which piece of
code is responsible for heap memory usage. See Execution Trees
for a detailed explanation about execution trees.
When set to none, no memory execution tree is produced.
When set to allocs, the memory execution tree gives the
current number of allocated bytes and the current number of
allocated blocks.
When set to full, the memory execution tree gives 6 different
measurements : the current number of allocated bytes and
blocks (same values as for allocs), the total number of
allocated bytes and blocks, the total number of freed bytes
and blocks.
Note that the overhead in cpu and memory to produce an xtree
depends on the tool. The overhead in cpu is small for the
value allocs, as the information needed to produce this report
is maintained in any case by the tool. For massif and
helgrind, specifying full implies to capture a stack trace for
each free operation, while normally these tools only capture
an allocation stack trace. For Memcheck, the cpu overhead for
the value full is small, as this can only be used in
combination with --keep-stacktraces=alloc-and-free or
--keep-stacktraces=alloc-then-free, which already records a
stack trace for each free operation. The memory overhead
varies between 5 and 10 words per unique stacktrace in the
xtree, plus the memory needed to record the stack trace for
the free operations, if needed specifically for the xtree.
--xtree-memory-file=<filename> [default: xtmemory.kcg.%p]
Specifies that Valgrind should produce the xtree memory report
in the specified file. Any %p or %q sequences appearing in the
filename are expanded in exactly the same way as they are for
--log-file. See the description of --log-file for details.
If the filename contains the extension .ms, then the produced
file format will be a massif output file format. If the
filename contains the extension .kcg or no extension is
provided or recognised, then the produced file format will be
a callgrind output format.
See Execution Trees for a detailed explanation about execution
trees formats.
These options apply to all tools, as they affect certain obscure
workings of the Valgrind core. Most people won't need to use them.
--smc-check=<none|stack|all|all-non-file> [default: all-non-file
for x86/amd64/s390x, stack for other archs]
This option controls Valgrind's detection of self-modifying
code. If no checking is done, when a program executes some
code, then overwrites it with new code, and executes the new
code, Valgrind will continue to execute the translations it
made for the old code. This will likely lead to incorrect
behaviour and/or crashes.
For "modern" architectures -- anything that's not x86, amd64
or s390x -- the default is stack. This is because a correct
program must take explicit action to reestablish D-I cache
coherence following code modification. Valgrind observes and
honours such actions, with the result that self-modifying code
is transparently handled with zero extra cost.
For x86, amd64 and s390x, the program is not required to
notify the hardware of required D-I coherence syncing. Hence
the default is all-non-file, which covers the normal case of
generating code into an anonymous (non-file-backed) mmap'd
area.
The meanings of the four available settings are as follows. No
detection (none), detect self-modifying code on the stack
(which is used by GCC to implement nested functions) (stack),
detect self-modifying code everywhere (all), and detect
self-modifying code everywhere except in file-backed mappings
(all-non-file).
Running with all will slow Valgrind down noticeably. Running
with none will rarely speed things up, since very little code
gets dynamically generated in most programs. The
VALGRIND_DISCARD_TRANSLATIONS client request is an alternative
to --smc-check=all and --smc-check=all-non-file that requires
more programmer effort but allows Valgrind to run your program
faster, by telling it precisely when translations need to be
re-made.
--smc-check=all-non-file provides a cheaper but more limited
version of --smc-check=all. It adds checks to any translations
that do not originate from file-backed memory mappings.
Typical applications that generate code, for example JITs in
web browsers, generate code into anonymous mmaped areas,
whereas the "fixed" code of the browser always lives in
file-backed mappings. --smc-check=all-non-file takes
advantage of this observation, limiting the overhead of
checking to code which is likely to be JIT generated.
--read-inline-info=<yes|no> [default: see below]
When enabled, Valgrind will read information about inlined
function calls from DWARF3 debug info. This slows Valgrind
startup and makes it use more memory (typically for each
inlined piece of code, 6 words and space for the function
name), but it results in more descriptive stacktraces.
Currently, this functionality is enabled by default only for
Linux, FreeBSD, Android and Solaris targets and only for the
tools Memcheck, Massif, Helgrind and DRD. Here is an example
of some stacktraces with --read-inline-info=no:
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x80484EA: main (inlinfo.c:6)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x8048550: fun_noninline (inlinfo.c:6)
==15380== by 0x804850E: main (inlinfo.c:34)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x8048520: main (inlinfo.c:6)
And here are the same errors with --read-inline-info=yes:
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x80484EA: fun_d (inlinfo.c:6)
==15377== by 0x80484EA: fun_c (inlinfo.c:14)
==15377== by 0x80484EA: fun_b (inlinfo.c:20)
==15377== by 0x80484EA: fun_a (inlinfo.c:26)
==15377== by 0x80484EA: main (inlinfo.c:33)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x8048550: fun_d (inlinfo.c:6)
==15377== by 0x8048550: fun_noninline (inlinfo.c:41)
==15377== by 0x804850E: main (inlinfo.c:34)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x8048520: fun_d (inlinfo.c:6)
==15377== by 0x8048520: main (inlinfo.c:35)
--read-var-info=<yes|no> [default: no]
When enabled, Valgrind will read information about variable
types and locations from DWARF3 debug info. This slows
Valgrind startup significantly and makes it use significantly
more memory, but for the tools that can take advantage of it
(Memcheck, Helgrind, DRD) it can result in more precise error
messages. For example, here are some standard errors issued by
Memcheck:
==15363== Uninitialised byte(s) found during client check request
==15363== at 0x80484A9: croak (varinfo1.c:28)
==15363== by 0x8048544: main (varinfo1.c:55)
==15363== Address 0x80497f7 is 7 bytes inside data symbol "global_i2"
==15363==
==15363== Uninitialised byte(s) found during client check request
==15363== at 0x80484A9: croak (varinfo1.c:28)
==15363== by 0x8048550: main (varinfo1.c:56)
==15363== Address 0xbea0d0cc is on thread 1's stack
==15363== in frame #1, created by main (varinfo1.c:45)
And here are the same errors with --read-var-info=yes:
==15370== Uninitialised byte(s) found during client check request
==15370== at 0x80484A9: croak (varinfo1.c:28)
==15370== by 0x8048544: main (varinfo1.c:55)
==15370== Location 0x80497f7 is 0 bytes inside global_i2[7],
==15370== a global variable declared at varinfo1.c:41
==15370==
==15370== Uninitialised byte(s) found during client check request
==15370== at 0x80484A9: croak (varinfo1.c:28)
==15370== by 0x8048550: main (varinfo1.c:56)
==15370== Location 0xbeb4a0cc is 0 bytes inside local var "local"
==15370== declared at varinfo1.c:46, in frame #1 of thread 1
--vgdb-poll=<number> [default: 5000]
As part of its main loop, the Valgrind scheduler will poll to
check if some activity (such as an external command or some
input from a gdb) has to be handled by gdbserver. This
activity poll will be done after having run the given number
of basic blocks (or slightly more than the given number of
basic blocks). This poll is quite cheap so the default value
is set relatively low. You might further decrease this value
if vgdb cannot use ptrace system call to interrupt Valgrind if
all threads are (most of the time) blocked in a system call.
--vgdb-shadow-registers=no|yes [default: no]
When activated, gdbserver will expose the Valgrind shadow
registers to GDB. With this, the value of the Valgrind shadow
registers can be examined or changed using GDB. Exposing
shadow registers only works with GDB version 7.1 or later.
--vgdb-prefix=<prefix> [default: /tmp/vgdb-pipe]
To communicate with gdb/vgdb, the Valgrind gdbserver creates 3
files (2 named FIFOs and a mmap shared memory file). The
prefix option controls the directory and prefix for the
creation of these files.
--run-libc-freeres=<yes|no> [default: yes]
This option is only relevant when running Valgrind on Linux
with GNU libc.
The GNU C library (libc.so), which is used by all programs,
may allocate memory for its own uses. Usually it doesn't
bother to free that memory when the program ends—there would
be no point, since the Linux kernel reclaims all process
resources when a process exits anyway, so it would just slow
things down.
The glibc authors realised that this behaviour causes leak
checkers, such as Valgrind, to falsely report leaks in glibc,
when a leak check is done at exit. In order to avoid this,
they provided a routine called __libc_freeres specifically to
make glibc release all memory it has allocated. Memcheck
therefore tries to run __libc_freeres at exit.
Unfortunately, in some very old versions of glibc,
__libc_freeres is sufficiently buggy to cause segmentation
faults. This was particularly noticeable on Red Hat 7.1. So
this option is provided in order to inhibit the run of
__libc_freeres. If your program seems to run fine on Valgrind,
but segfaults at exit, you may find that --run-libc-freeres=no
fixes that, although at the cost of possibly falsely reporting
space leaks in libc.so.
--run-cxx-freeres=<yes|no> [default: yes]
This option is only relevant when running Valgrind on Linux,
FreeBSD or Solaris C++ programs using libstdc++.
The GNU Standard C++ library (libstdc++.so), which is used by
all C++ programs compiled with g++, may allocate memory for
its own uses. Usually it doesn't bother to free that memory
when the program ends—there would be no point, since the
kernel reclaims all process resources when a process exits
anyway, so it would just slow things down.
The gcc authors realised that this behaviour causes leak
checkers, such as Valgrind, to falsely report leaks in
libstdc++, when a leak check is done at exit. In order to
avoid this, they provided a routine called
__gnu_cxx::__freeres specifically to make libstdc++ release
all memory it has allocated. Memcheck therefore tries to run
__gnu_cxx::__freeres at exit.
For the sake of flexibility and unforeseen problems with
__gnu_cxx::__freeres, option --run-cxx-freeres=no exists,
although at the cost of possibly falsely reporting space leaks
in libstdc++.so.
--sim-hints=hint1,hint2,...
Pass miscellaneous hints to Valgrind which slightly modify the
simulated behaviour in nonstandard or dangerous ways, possibly
to help the simulation of strange features. By default no
hints are enabled. Use with caution! Currently known hints
are:
• lax-ioctls: Be very lax about ioctl handling; the only
assumption is that the size is correct. Doesn't require
the full buffer to be initialised when writing. Without
this, using some device drivers with a large number of
strange ioctl commands becomes very tiresome.
• fuse-compatible: Enable special handling for certain
system calls that may block in a FUSE file-system. This
may be necessary when running Valgrind on a multi-threaded
program that uses one thread to manage a FUSE file-system
and another thread to access that file-system.
• enable-outer: Enable some special magic needed when the
program being run is itself Valgrind.
• no-inner-prefix: Disable printing a prefix > in front of
each stdout or stderr output line in an inner Valgrind
being run by an outer Valgrind. This is useful when
running Valgrind regression tests in an outer/inner setup.
Note that the prefix > will always be printed in front of
the inner debug logging lines.
• no-nptl-pthread-stackcache: This hint is only relevant
when running Valgrind on Linux; it is ignored on FreeBSD,
Solaris and macOS.
The GNU glibc pthread library (libpthread.so), which is
used by pthread programs, maintains a cache of pthread
stacks. When a pthread terminates, the memory used for the
pthread stack and some thread local storage related data
structure are not always directly released. This memory is
kept in a cache (up to a certain size), and is re-used if
a new thread is started.
This cache causes the helgrind tool to report some false
positive race condition errors on this cached memory, as
helgrind does not understand the internal glibc cache
synchronisation primitives. So, when using helgrind,
disabling the cache helps to avoid false positive race
conditions, in particular when using thread local storage
variables (e.g. variables using the __thread qualifier).
When using the memcheck tool, disabling the cache ensures
the memory used by glibc to handle __thread variables is
directly released when a thread terminates.
Note: Valgrind disables the cache using some internal
knowledge of the glibc stack cache implementation and by
examining the debug information of the pthread library.
This technique is thus somewhat fragile and might not work
for all glibc versions. This has been successfully tested
with various glibc versions (e.g. 2.11, 2.16, 2.18) on
various platforms.
• lax-doors: (Solaris only) Be very lax about door syscall
handling over unrecognised door file descriptors. Does not
require that full buffer is initialised when writing.
Without this, programs using libdoor(3LIB) functionality
with completely proprietary semantics may report large
number of false positives.
• fallback-llsc: (MIPS and ARM64 only): Enables an
alternative implementation of Load-Linked (LL) and
Store-Conditional (SC) instructions. The standard
implementation gives more correct behaviour, but can cause
indefinite looping on certain processor implementations
that are intolerant of extra memory references between LL
and SC. So far this is known only to happen on Cavium 3
cores. You should not need to use this flag, since the
relevant cores are detected at startup and the alternative
implementation is automatically enabled if necessary.
There is no equivalent anti-flag: you cannot force-disable
the alternative implementation, if it is automatically
enabled. The underlying problem exists because the
"standard" implementation of LL and SC is done by copying
through LL and SC instructions into the instrumented code.
However, tools may insert extra instrumentation memory
references in between the LL and SC instructions. These
memory references are not present in the original
uninstrumented code, and their presence in the
instrumented code can cause the SC instructions to
persistently fail, leading to indefinite looping in LL-SC
blocks. The alternative implementation gives correct
behaviour of LL and SC instructions between threads in a
process, up to and including the ABA scenario. It also
gives correct behaviour between a Valgrinded thread and a
non-Valgrinded thread running in a different process, that
communicate via shared memory, but only up to and
including correct CAS behaviour -- in this case the ABA
scenario may not be correctly handled.
--scheduling-quantum=<number> [default: 100000]
The --scheduling-quantum option controls the maximum number of
basic blocks executed by a thread before releasing the lock
used by Valgrind to serialise thread execution. Smaller values
give finer interleaving but increases the scheduling overhead.
Finer interleaving can be useful to reproduce race conditions
with helgrind or DRD. For more details about the Valgrind
thread serialisation scheme and its impact on performance and
thread scheduling, see Scheduling and Multi-Thread
Performance.
--fair-sched=<no|yes|try> [default: no]
The --fair-sched option controls the locking mechanism used by
Valgrind to serialise thread execution. The locking mechanism
controls the way the threads are scheduled, and different
settings give different trade-offs between fairness and
performance. For more details about the Valgrind thread
serialisation scheme and its impact on performance and thread
scheduling, see Scheduling and Multi-Thread Performance.
• The value --fair-sched=yes activates a fair scheduler. In
short, if multiple threads are ready to run, the threads
will be scheduled in a round robin fashion. This mechanism
is not available on all platforms or Linux versions. If
not available, using --fair-sched=yes will cause Valgrind
to terminate with an error.
You may find this setting improves overall responsiveness
if you are running an interactive multithreaded program,
for example a web browser, on Valgrind.
• The value --fair-sched=try activates fair scheduling if
available on the platform. Otherwise, it will
automatically fall back to --fair-sched=no.
• The value --fair-sched=no activates a scheduler which does
not guarantee fairness between threads ready to run, but
which in general gives the highest performance.
--kernel-variant=variant1,variant2,...
Handle system calls and ioctls arising from minor variants of
the default kernel for this platform. This is useful for
running on hacked kernels or with kernel modules which support
nonstandard ioctls, for example. Use with caution. If you
don't understand what this option does then you almost
certainly don't need it. Currently known variants are:
• bproc: support the sys_broc system call on x86. This is
for running on BProc, which is a minor variant of standard
Linux which is sometimes used for building clusters.
• android-no-hw-tls: some versions of the Android emulator
for ARM do not provide a hardware TLS (thread-local state)
register, and Valgrind crashes at startup. Use this
variant to select software support for TLS.
• android-gpu-sgx5xx: use this to support handling of
proprietary ioctls for the PowerVR SGX 5XX series of GPUs
on Android devices. Failure to select this does not cause
stability problems, but may cause Memcheck to report false
errors after the program performs GPU-specific ioctls.
• android-gpu-adreno3xx: similarly, use this to support
handling of proprietary ioctls for the Qualcomm Adreno 3XX
series of GPUs on Android devices.
--merge-recursive-frames=<number> [default: 0]
Some recursive algorithms, for example balanced binary tree
implementations, create many different stack traces, each
containing cycles of calls. A cycle is defined as two
identical program counter values separated by zero or more
other program counter values. Valgrind may then use a lot of
memory to store all these stack traces. This is a poor use of
memory considering that such stack traces contain repeated
uninteresting recursive calls instead of more interesting
information such as the function that has initiated the
recursive call.
The option --merge-recursive-frames=<number> instructs
Valgrind to detect and merge recursive call cycles having a
size of up to <number> frames. When such a cycle is detected,
Valgrind records the cycle in the stack trace as a unique
program counter.
The value 0 (the default) causes no recursive call merging. A
value of 1 will cause stack traces of simple recursive
algorithms (for example, a factorial implementation) to be
collapsed. A value of 2 will usually be needed to collapse
stack traces produced by recursive algorithms such as binary
trees, quick sort, etc. Higher values might be needed for more
complex recursive algorithms.
Note: recursive calls are detected by analysis of program
counter values. They are not detected by looking at function
names.
--num-transtab-sectors=<number> [default: 6 for Android platforms,
16 for all others]
Valgrind translates and instruments your program's machine
code in small fragments (basic blocks). The translations are
stored in a translation cache that is divided into a number of
sections (sectors). If the cache is full, the sector
containing the oldest translations is emptied and reused. If
these old translations are needed again, Valgrind must
re-translate and re-instrument the corresponding machine code,
which is expensive. If the "executed instructions" working set
of a program is big, increasing the number of sectors may
improve performance by reducing the number of re-translations
needed. Sectors are allocated on demand. Once allocated, a
sector can never be freed, and occupies considerable space,
depending on the tool and the value of
--avg-transtab-entry-size (about 40 MB per sector for
Memcheck). Use the option --stats=yes to obtain precise
information about the memory used by a sector and the
allocation and recycling of sectors.
--avg-transtab-entry-size=<number> [default: 0, meaning use tool
provided default]
Average size of translated basic block. This average size is
used to dimension the size of a sector. Each tool provides a
default value to be used. If this default value is too small,
the translation sectors will become full too quickly. If this
default value is too big, a significant part of the
translation sector memory will be unused. Note that the
average size of a basic block translation depends on the tool,
and might depend on tool options. For example, the memcheck
option --track-origins=yes increases the size of the basic
block translations. Use --avg-transtab-entry-size to tune the
size of the sectors, either to gain memory or to avoid too
many retranslations.
--aspace-minaddr=<address> [default: depends on the platform]
To avoid potential conflicts with some system libraries,
Valgrind does not use the address space below --aspace-minaddr
value, keeping it reserved in case a library specifically
requests memory in this region. So, some "pessimistic" value
is guessed by Valgrind depending on the platform. On linux, by
default, Valgrind avoids using the first 64MB even if
typically there is no conflict in this complete zone. You can
use the option --aspace-minaddr to have your memory hungry
application benefitting from more of this lower memory. On the
other hand, if you encounter a conflict, increasing
aspace-minaddr value might solve it. Conflicts will typically
manifest themselves with mmap failures in the low range of the
address space. The provided address must be page aligned and
must be equal or bigger to 0x1000 (4KB). To find the default
value on your platform, do something such as valgrind -d -d
date 2>&1 | grep -i minaddr. Values lower than 0x10000 (64KB)
are known to create problems on some distributions.
--valgrind-stacksize=<number> [default: 1MB]
For each thread, Valgrind needs its own 'private' stack. The
default size for these stacks is largely dimensioned, and so
should be sufficient in most cases. In case the size is too
small, Valgrind will segfault. Before segfaulting, a warning
might be produced by Valgrind when approaching the limit.
Use the option --valgrind-stacksize if such an (unlikely)
warning is produced, or Valgrind dies due to a segmentation
violation. Such segmentation violations have been seen when
demangling huge C++ symbols.
If your application uses many threads and needs a lot of
memory, you can gain some memory by reducing the size of these
Valgrind stacks using the option --valgrind-stacksize.
--show-emwarns=<yes|no> [default: no]
When enabled, Valgrind will emit warnings about its CPU
emulation in certain cases. These are usually not interesting.
--require-text-symbol=:sonamepatt:fnnamepatt
When a shared object whose soname matches sonamepatt is loaded
into the process, examine all the text symbols it exports. If
none of those match fnnamepatt, print an error message and
abandon the run. This makes it possible to ensure that the run
does not continue unless a given shared object contains a
particular function name.
Both sonamepatt and fnnamepatt can be written using the usual
? and * wildcards. For example: ":*libc.so*:foo?bar". You may
use characters other than a colon to separate the two
patterns. It is only important that the first character and
the separator character are the same. For example, the above
example could also be written "Q*libc.so*Qfoo?bar". Multiple
--require-text-symbol flags are allowed, in which case shared
objects that are loaded into the process will be checked
against all of them.
The purpose of this is to support reliable usage of marked-up
libraries. For example, suppose we have a version of GCC's
libgomp.so which has been marked up with annotations to
support Helgrind. It is only too easy and confusing to load
the wrong, un-annotated libgomp.so into the application. So
the idea is: add a text symbol in the marked-up library, for
example annotated_for_helgrind_3_6, and then give the flag
--require-text-symbol=:*libgomp*so*:annotated_for_helgrind_3_6
so that when libgomp.so is loaded, Valgrind scans its symbol
table, and if the symbol isn't present the run is aborted,
rather than continuing silently with the un-marked-up library.
Note that you should put the entire flag in quotes to stop
shells expanding up the * and ? wildcards.
--soname-synonyms=syn1=pattern1,syn2=pattern2,...
When a shared library is loaded, Valgrind checks for functions
in the library that must be replaced or wrapped. For example,
Memcheck replaces some string and memory functions (strchr,
strlen, strcpy, memchr, memcpy, memmove, etc.) with its own
versions. Such replacements are normally done only in shared
libraries whose soname matches a predefined soname pattern
(e.g. libc.so* on linux). By default, no replacement is done
for a statically linked binary or for alternative libraries,
except for the allocation functions (malloc, free, calloc,
memalign, realloc, operator new, operator delete, etc.) Such
allocation functions are intercepted by default in any shared
library or in the executable if they are exported as global
symbols. This means that if a replacement allocation library
such as tcmalloc is found, its functions are also intercepted
by default. In some cases, the replacements allow
--soname-synonyms to specify one additional synonym pattern,
giving flexibility in the replacement. Or to prevent
interception of all public allocation symbols.
Currently, this flexibility is only allowed for the malloc
related functions, using the synonym somalloc. This synonym is
usable for all tools doing standard replacement of malloc
related functions (e.g. memcheck, helgrind, drd, massif,
dhat).
• Alternate malloc library: to replace the malloc related
functions in a specific alternate library with soname
mymalloclib.so (and not in any others), give the option
--soname-synonyms=somalloc=mymalloclib.so. A pattern can
be used to match multiple libraries sonames. For example,
--soname-synonyms=somalloc=*tcmalloc* will match the
soname of all variants of the tcmalloc library (native,
debug, profiled, ... tcmalloc variants).
Note: the soname of a elf shared library can be retrieved
using the readelf utility.
• Replacements in a statically linked library are done by
using the NONE pattern. For example, if you link with
libtcmalloc.a, and only want to intercept the malloc
related functions in the executable (and standard
libraries) themselves, but not any other shared libraries,
you can give the option --soname-synonyms=somalloc=NONE.
Note that a NONE pattern will match the main executable
and any shared library having no soname.
• To only intercept allocation symbols in the default system
libraries, but not in any other shared library or the
executable defining public malloc or operator new related
functions use a non-existing library name like
--soname-synonyms=somalloc=nouserintercepts (where
nouserintercepts can be any non-existing library name).
• Shared library of the dynamic (runtime) linker is excluded
from searching for global public symbols, such as those
for the malloc related functions (identified by somalloc
synonym).
--progress-interval=<number> [default: 0, meaning 'disabled']
This is an enhancement to Valgrind's debugging output. It is
unlikely to be of interest to end users.
When number is set to a non-zero value, Valgrind will print a
one-line progress summary every number seconds. Valid settings
for number are between 0 and 3600 inclusive. Here's some
example output with number set to 10:
PROGRESS: U 110s, W 113s, 97.3% CPU, EvC 414.79M, TIn 616.7k, TOut 0.5k, #thr 67
PROGRESS: U 120s, W 124s, 96.8% CPU, EvC 505.27M, TIn 636.6k, TOut 3.0k, #thr 64
PROGRESS: U 130s, W 134s, 97.0% CPU, EvC 574.90M, TIn 657.5k, TOut 3.0k, #thr 63
Each line shows:
• U: total user time
• W: total wallclock time
• CPU: overall average cpu use
• EvC: number of event checks. An event check is a backwards
branch in the simulated program, so this is a measure of
forward progress of the program
• TIn: number of code blocks instrumented by the JIT
• TOut: number of instrumented code blocks that have been
thrown away
• #thr: number of threads in the program
From the progress of these, it is possible to observe:
• when the program is compute bound (TIn rises slowly, EvC
rises rapidly)
• when the program is in a spinloop (TIn/TOut fixed, EvC
rises rapidly)
• when the program is JIT-bound (TIn rises rapidly)
• when the program is rapidly discarding code (TOut rises
rapidly)
• when the program is about to achieve some expected state
(EvC arrives at some value you expect)
• when the program is idling (U rises more slowly than W)
There are also some options for debugging Valgrind itself. You
shouldn't need to use them in the normal run of things. If you
wish to see the list, use the --help-debug option.
--leak-check=<no|summary|yes|full> [default: summary]
When enabled, search for memory leaks when the client program
finishes. If set to summary, it says how many leaks occurred.
If set to full or yes, each individual leak will be shown in
detail and/or counted as an error, as specified by the options
--show-leak-kinds and --errors-for-leak-kinds.
If --xml=yes is given, memcheck will automatically use the
value --leak-check=full. You can use --show-leak-kinds=none to
reduce the size of the xml output if you are not interested in
the leak results.
--leak-resolution=<low|med|high> [default: high]
When doing leak checking, determines how willing Memcheck is
to consider different backtraces to be the same for the
purposes of merging multiple leaks into a single leak report.
When set to low, only the first two entries need match. When
med, four entries have to match. When high, all entries need
to match.
For hardcore leak debugging, you probably want to use
--leak-resolution=high together with --num-callers=40 or some
such large number.
Note that the --leak-resolution setting does not affect
Memcheck's ability to find leaks. It only changes how the
results are presented.
--show-leak-kinds=<set> [default: definite,possible]
Specifies the leak kinds to show in a full leak search, in one
of the following ways:
• a comma separated list of one or more of definite indirect
possible reachable.
• all to specify the complete set (all leak kinds). It is
equivalent to
--show-leak-kinds=definite,indirect,possible,reachable.
• none for the empty set.
--errors-for-leak-kinds=<set> [default: definite,possible]
Specifies the leak kinds to count as errors in a full leak
search. The <set> is specified similarly to --show-leak-kinds
--leak-check-heuristics=<set> [default: all]
Specifies the set of leak check heuristics to be used during
leak searches. The heuristics control which interior pointers
to a block cause it to be considered as reachable. The
heuristic set is specified in one of the following ways:
• a comma separated list of one or more of stdstring
length64 newarray multipleinheritance.
• all to activate the complete set of heuristics. It is
equivalent to
--leak-check-heuristics=stdstring,length64,newarray,multipleinheritance.
• none for the empty set.
Note that these heuristics are dependent on the layout of the
objects produced by the C++ compiler. They have been tested
with some gcc versions (e.g. 4.4 and 4.7). They might not work
properly with other C++ compilers.
--show-reachable=<yes|no> , --show-possibly-lost=<yes|no>
These options provide an alternative way to specify the leak
kinds to show:
• --show-reachable=no --show-possibly-lost=yes is equivalent
to --show-leak-kinds=definite,possible.
• --show-reachable=no --show-possibly-lost=no is equivalent
to --show-leak-kinds=definite.
• --show-reachable=yes is equivalent to
--show-leak-kinds=all.
Note that --show-possibly-lost=no has no effect if
--show-reachable=yes is specified.
--xtree-leak=<no|yes> [no]
If set to yes, the results for the leak search done at exit
will be output in a 'Callgrind Format' execution tree file.
Note that this automatically sets the options
--leak-check=full and --show-leak-kinds=all, to allow xtree
visualisation tools such as kcachegrind to select what kind to
leak to visualize. The produced file will contain the
following events:
• RB : Reachable Bytes
• PB : Possibly lost Bytes
• IB : Indirectly lost Bytes
• DB : Definitely lost Bytes (direct plus indirect)
• DIB : Definitely Indirectly lost Bytes (subset of DB)
• RBk : reachable Blocks
• PBk : Possibly lost Blocks
• IBk : Indirectly lost Blocks
• DBk : Definitely lost Blocks
The increase or decrease for all events above will also be
output in the file to provide the delta (increase or decrease)
between 2 successive leak searches. For example, iRB is the
increase of the RB event, dPBk is the decrease of PBk event.
The values for the increase and decrease events will be zero
for the first leak search done.
See Execution Trees for a detailed explanation about execution
trees.
--xtree-leak-file=<filename> [default: xtleak.kcg.%p]
Specifies that Valgrind should produce the xtree leak report
in the specified file. Any %p, %q or %n sequences appearing in
the filename are expanded in exactly the same way as they are
for --log-file. See the description of --log-file for details.
See Execution Trees for a detailed explanation about execution
trees formats.
--undef-value-errors=<yes|no> [default: yes]
Controls whether Memcheck reports uses of undefined value
errors. Set this to no if you don't want to see undefined
value errors. It also has the side effect of speeding up
Memcheck somewhat. AddrCheck (removed in Valgrind 3.1.0)
functioned like Memcheck with --undef-value-errors=no.
--track-origins=<yes|no> [default: no]
Controls whether Memcheck tracks the origin of uninitialised
values. By default, it does not, which means that although it
can tell you that an uninitialised value is being used in a
dangerous way, it cannot tell you where the uninitialised
value came from. This often makes it difficult to track down
the root problem.
When set to yes, Memcheck keeps track of the origins of all
uninitialised values. Then, when an uninitialised value error
is reported, Memcheck will try to show the origin of the
value. An origin can be one of the following four places: a
heap block, a stack allocation, a client request, or
miscellaneous other sources (eg, a call to brk).
For uninitialised values originating from a heap block,
Memcheck shows where the block was allocated. For
uninitialised values originating from a stack allocation,
Memcheck can tell you which function allocated the value, but
no more than that -- typically it shows you the source
location of the opening brace of the function. So you should
carefully check that all of the function's local variables are
initialised properly.
Performance overhead: origin tracking is expensive. It halves
Memcheck's speed and increases memory use by a minimum of
100MB, and possibly more. Nevertheless it can drastically
reduce the effort required to identify the root cause of
uninitialised value errors, and so is often a programmer
productivity win, despite running more slowly.
Accuracy: Memcheck tracks origins quite accurately. To avoid
very large space and time overheads, some approximations are
made. It is possible, although unlikely, that Memcheck will
report an incorrect origin, or not be able to identify any
origin.
Note that the combination --track-origins=yes and
--undef-value-errors=no is nonsensical. Memcheck checks for
and rejects this combination at startup.
--partial-loads-ok=<yes|no> [default: yes]
Controls how Memcheck handles 32-, 64-, 128- and 256-bit
naturally aligned loads from addresses for which some bytes
are addressable and others are not. When yes, such loads do
not produce an address error. Instead, loaded bytes
originating from illegal addresses are marked as
uninitialised, and those corresponding to legal addresses are
handled in the normal way.
When no, loads from partially invalid addresses are treated
the same as loads from completely invalid addresses: an
illegal-address error is issued, and the resulting bytes are
marked as initialised.
Note that code that behaves in this way is in violation of the
ISO C/C++ standards, and should be considered broken. If at
all possible, such code should be fixed.
--expensive-definedness-checks=<no|auto|yes> [default: auto]
Controls whether Memcheck should employ more precise but also
more expensive (time consuming) instrumentation when checking
the definedness of certain values. In particular, this affects
the instrumentation of integer adds, subtracts and equality
comparisons.
Selecting --expensive-definedness-checks=yes causes Memcheck
to use the most accurate analysis possible. This minimises
false error rates but can cause up to 30% performance
degradation.
Selecting --expensive-definedness-checks=no causes Memcheck to
use the cheapest instrumentation possible. This maximises
performance but will normally give an unusably high false
error rate.
The default setting, --expensive-definedness-checks=auto, is
strongly recommended. This causes Memcheck to use the minimum
of expensive instrumentation needed to achieve the same false
error rate as --expensive-definedness-checks=yes. It also
enables an instrumentation-time analysis pass which aims to
further reduce the costs of accurate instrumentation. Overall,
the performance loss is generally around 5% relative to
--expensive-definedness-checks=no, although this is strongly
workload dependent. Note that the exact instrumentation
settings in this mode are architecture dependent.
--keep-stacktraces=alloc|free|alloc-and-free|alloc-then-free|none
[default: alloc-and-free]
Controls which stack trace(s) to keep for malloc'd and/or
free'd blocks.
With alloc-then-free, a stack trace is recorded at allocation
time, and is associated with the block. When the block is
freed, a second stack trace is recorded, and this replaces the
allocation stack trace. As a result, any "use after free"
errors relating to this block can only show a stack trace for
where the block was freed.
With alloc-and-free, both allocation and the deallocation
stack traces for the block are stored. Hence a "use after
free" error will show both, which may make the error easier to
diagnose. Compared to alloc-then-free, this setting slightly
increases Valgrind's memory use as the block contains two
references instead of one.
With alloc, only the allocation stack trace is recorded (and
reported). With free, only the deallocation stack trace is
recorded (and reported). These values somewhat decrease
Valgrind's memory and cpu usage. They can be useful depending
on the error types you are searching for and the level of
detail you need to analyse them. For example, if you are only
interested in memory leak errors, it is sufficient to record
the allocation stack traces.
With none, no stack traces are recorded for malloc and free
operations. If your program allocates a lot of blocks and/or
allocates/frees from many different stack traces, this can
significantly decrease cpu and/or memory required. Of course,
few details will be reported for errors related to heap
blocks.
Note that once a stack trace is recorded, Valgrind keeps the
stack trace in memory even if it is not referenced by any
block. Some programs (for example, recursive algorithms) can
generate a huge number of stack traces. If Valgrind uses too
much memory in such circumstances, you can reduce the memory
required with the options --keep-stacktraces and/or by using a
smaller value for the option --num-callers.
If you want to use --xtree-memory=full memory profiling (see
Execution Trees), then you cannot specify
--keep-stacktraces=free or --keep-stacktraces=none.
--freelist-vol=<number> [default: 20000000]
When the client program releases memory using free (in C) or
delete (C++), that memory is not immediately made available
for re-allocation. Instead, it is marked inaccessible and
placed in a queue of freed blocks. The purpose is to defer as
long as possible the point at which freed-up memory comes back
into circulation. This increases the chance that Memcheck will
be able to detect invalid accesses to blocks for some
significant period of time after they have been freed.
This option specifies the maximum total size, in bytes, of the
blocks in the queue. The default value is twenty million
bytes. Increasing this increases the total amount of memory
used by Memcheck but may detect invalid uses of freed blocks
which would otherwise go undetected.
--freelist-big-blocks=<number> [default: 1000000]
When making blocks from the queue of freed blocks available
for re-allocation, Memcheck will in priority re-circulate the
blocks with a size greater or equal to --freelist-big-blocks.
This ensures that freeing big blocks (in particular freeing
blocks bigger than --freelist-vol) does not immediately lead
to a re-circulation of all (or a lot of) the small blocks in
the free list. In other words, this option increases the
likelihood to discover dangling pointers for the "small"
blocks, even when big blocks are freed.
Setting a value of 0 means that all the blocks are
re-circulated in a FIFO order.
--workaround-gcc296-bugs=<yes|no> [default: no]
When enabled, assume that reads and writes some small distance
below the stack pointer are due to bugs in GCC 2.96, and does
not report them. The "small distance" is 256 bytes by default.
Note that GCC 2.96 is the default compiler on some ancient
Linux distributions (RedHat 7.X) and so you may need to use
this option. Do not use it if you do not have to, as it can
cause real errors to be overlooked. A better alternative is to
use a more recent GCC in which this bug is fixed.
You may also need to use this option when working with GCC 3.X
or 4.X on 32-bit PowerPC Linux. This is because GCC generates
code which occasionally accesses below the stack pointer,
particularly for floating-point to/from integer conversions.
This is in violation of the 32-bit PowerPC ELF specification,
which makes no provision for locations below the stack pointer
to be accessible.
This option is deprecated as of version 3.12 and may be
removed from future versions. You should instead use
--ignore-range-below-sp to specify the exact range of offsets
below the stack pointer that should be ignored. A suitable
equivalent is --ignore-range-below-sp=1024-1.
--ignore-range-below-sp=<number>-<number>
This is a more general replacement for the deprecated
--workaround-gcc296-bugs option. When specified, it causes
Memcheck not to report errors for accesses at the specified
offsets below the stack pointer. The two offsets must be
positive decimal numbers and -- somewhat counterintuitively --
the first one must be larger, in order to imply a
non-wraparound address range to ignore. For example, to ignore
4 byte accesses at 8192 bytes below the stack pointer, use
--ignore-range-below-sp=8192-8189. Only one range may be
specified.
--show-mismatched-frees=<yes|no> [default: yes]
When enabled, Memcheck checks that heap blocks are deallocated
using a function that matches the allocating function. That
is, it expects free to be used to deallocate blocks allocated
by malloc, delete for blocks allocated by new, and delete[]
for blocks allocated by new[]. If a mismatch is detected, an
error is reported. This is in general important because in
some environments, freeing with a non-matching function can
cause crashes.
There is however a scenario where such mismatches cannot be
avoided. That is when the user provides implementations of
new/new[] that call malloc and of delete/delete[] that call
free, and these functions are asymmetrically inlined. For
example, imagine that delete[] is inlined but new[] is not.
The result is that Memcheck "sees" all delete[] calls as
direct calls to free, even when the program source contains no
mismatched calls.
This causes a lot of confusing and irrelevant error reports.
--show-mismatched-frees=no disables these checks. It is not
generally advisable to disable them, though, because you may
miss real errors as a result.
--show-realloc-size-zero=<yes|no> [default: yes]
When enabled, Memcheck checks for uses of realloc with a size
of zero. This usage of realloc is unsafe since it is not
portable. On some systems it will behave like free. On other
systems it will either do nothing or else behave like a call
to free followed by a call to malloc with a size of zero.
--ignore-ranges=0xPP-0xQQ[,0xRR-0xSS]
Any ranges listed in this option (and multiple ranges can be
specified, separated by commas) will be ignored by Memcheck's
addressability checking.
--malloc-fill=<hexnumber>
Fills blocks allocated by malloc, new, etc, but not by calloc,
with the specified byte. This can be useful when trying to
shake out obscure memory corruption problems. The allocated
area is still regarded by Memcheck as undefined -- this option
only affects its contents. Note that --malloc-fill does not
affect a block of memory when it is used as argument to client
requests VALGRIND_MEMPOOL_ALLOC or VALGRIND_MALLOCLIKE_BLOCK.
--free-fill=<hexnumber>
Fills blocks freed by free, delete, etc, with the specified
byte value. This can be useful when trying to shake out
obscure memory corruption problems. The freed area is still
regarded by Memcheck as not valid for access -- this option
only affects its contents. Note that --free-fill does not
affect a block of memory when it is used as argument to client
requests VALGRIND_MEMPOOL_FREE or VALGRIND_FREELIKE_BLOCK.
--cachegrind-out-file=<file>
Write the Cachegrind output file to file rather than to the
default output file, cachegrind.out.<pid>. The %p and %q
format specifiers can be used to embed the process ID and/or
the contents of an environment variable in the name, as is the
case for the core option --log-file.
--cache-sim=no|yes [no]
Enables or disables collection of cache access and miss
counts.
--branch-sim=no|yes [no]
Enables or disables collection of branch instruction and
misprediction counts.
--instr-at-start=no|yes [yes]
Enables or disables instrumentation at the start of execution.
Use this in combination with CACHEGRIND_START_INSTRUMENTATION
and CACHEGRIND_STOP_INSTRUMENTATION to measure only part of a
client program's execution.
--I1=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 1
instruction cache. Only useful with --cache-sim=yes.
--D1=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 1
data cache. Only useful with --cache-sim=yes.
--LL=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the
last-level cache. Only useful with --cache-sim=yes.
--callgrind-out-file=<file>
Write the profile data to file rather than to the default
output file, callgrind.out.<pid>. The %p and %q format
specifiers can be used to embed the process ID and/or the
contents of an environment variable in the name, as is the
case for the core option --log-file. When multiple dumps are
made, the file name is modified further; see below.
--dump-line=<no|yes> [default: yes]
This specifies that event counting should be performed at
source line granularity. This allows source annotation for
sources which are compiled with debug information (-g).
--dump-instr=<no|yes> [default: no]
This specifies that event counting should be performed at
per-instruction granularity. This allows for assembly code
annotation. Currently the results can only be displayed by
KCachegrind.
--compress-strings=<no|yes> [default: yes]
This option influences the output format of the profile data.
It specifies whether strings (file and function names) should
be identified by numbers. This shrinks the file, but makes it
more difficult for humans to read (which is not recommended in
any case).
--compress-pos=<no|yes> [default: yes]
This option influences the output format of the profile data.
It specifies whether numerical positions are always specified
as absolute values or are allowed to be relative to previous
numbers. This shrinks the file size.
--combine-dumps=<no|yes> [default: no]
When enabled, when multiple profile data parts are to be
generated these parts are appended to the same output file.
Not recommended.
--dump-every-bb=<count> [default: 0, never]
Dump profile data every count basic blocks. Whether a dump is
needed is only checked when Valgrind's internal scheduler is
run. Therefore, the minimum setting useful is about 100000.
The count is a 64-bit value to make long dump periods
possible.
--dump-before=<function>
Dump when entering function.
--zero-before=<function>
Zero all costs when entering function.
--dump-after=<function>
Dump when leaving function.
--instr-atstart=<yes|no> [default: yes]
Specify if you want Callgrind to start simulation and
profiling from the beginning of the program. When set to no,
Callgrind will not be able to collect any information,
including calls, but it will have at most a slowdown of around
4, which is the minimum Valgrind overhead. Instrumentation can
be interactively enabled via callgrind_control -i on.
Note that the resulting call graph will most probably not
contain main, but will contain all the functions executed
after instrumentation was enabled. Instrumentation can also be
programmatically enabled/disabled. See the Callgrind include
file callgrind.h for the macro you have to use in your source
code.
For cache simulation, results will be less accurate when
switching on instrumentation later in the program run, as the
simulator starts with an empty cache at that moment. Switch on
event collection later to cope with this error.
--collect-atstart=<yes|no> [default: yes]
Specify whether event collection is enabled at beginning of
the profile run.
To only look at parts of your program, you have two
possibilities:
1. Zero event counters before entering the program part you
want to profile, and dump the event counters to a file
after leaving that program part.
2. Switch on/off collection state as needed to only see event
counters happening while inside of the program part you
want to profile.
The second option can be used if the program part you want to
profile is called many times. Option 1, i.e. creating a lot of
dumps is not practical here.
Collection state can be toggled at entry and exit of a given
function with the option --toggle-collect. If you use this
option, collection state should be disabled at the beginning.
Note that the specification of --toggle-collect implicitly
sets --collect-state=no.
Collection state can be toggled also by inserting the client
request CALLGRIND_TOGGLE_COLLECT ; at the needed code
positions.
--toggle-collect=<function>
Toggle collection on entry/exit of function.
--collect-jumps=<no|yes> [default: no]
This specifies whether information for (conditional) jumps
should be collected. As above, callgrind_annotate currently is
not able to show you the data. You have to use KCachegrind to
get jump arrows in the annotated code.
--collect-systime=<no|yes|msec|usec|nsec> [default: no]
This specifies whether information for system call times
should be collected.
The value no indicates to record no system call information.
The other values indicate to record the number of system calls
done (sysCount event) and the elapsed time (sysTime event)
spent in system calls. The --collect-systime value gives the
unit used for sysTime : milli seconds, micro seconds or nano
seconds. With the value nsec, callgrind also records the cpu
time spent during system calls (sysCpuTime).
The value yes is a synonym of msec. The value nsec is not
supported on Darwin.
--collect-bus=<no|yes> [default: no]
This specifies whether the number of global bus events
executed should be collected. The event type "Ge" is used for
these events.
--cache-sim=<yes|no> [default: no]
Specify if you want to do full cache simulation. By default,
only instruction read accesses will be counted ("Ir"). With
cache simulation, further event counters are enabled: Cache
misses on instruction reads ("I1mr"/"ILmr"), data read
accesses ("Dr") and related cache misses ("D1mr"/"DLmr"), data
write accesses ("Dw") and related cache misses
("D1mw"/"DLmw"). For more information, see Cachegrind: a cache
and branch-prediction profiler.
--branch-sim=<yes|no> [default: no]
Specify if you want to do branch prediction simulation.
Further event counters are enabled: Number of executed
conditional branches and related predictor misses
("Bc"/"Bcm"), executed indirect jumps and related misses of
the jump address predictor ("Bi"/"Bim").
--free-is-write=no|yes [default: no]
When enabled (not the default), Helgrind treats freeing of
heap memory as if the memory was written immediately before
the free. This exposes races where memory is referenced by one
thread, and freed by another, but there is no observable
synchronisation event to ensure that the reference happens
before the free.
This functionality is new in Valgrind 3.7.0, and is regarded
as experimental. It is not enabled by default because its
interaction with custom memory allocators is not well
understood at present. User feedback is welcomed.
--track-lockorders=no|yes [default: yes]
When enabled (the default), Helgrind performs lock order
consistency checking. For some buggy programs, the large
number of lock order errors reported can become annoying,
particularly if you're only interested in race errors. You may
therefore find it helpful to disable lock order checking.
--history-level=none|approx|full [default: full]
--history-level=full (the default) causes Helgrind collects
enough information about "old" accesses that it can produce
two stack traces in a race report -- both the stack trace for
the current access, and the trace for the older, conflicting
access. To limit memory usage, "old" accesses stack traces are
limited to a maximum of --history-backtrace-size entries
(default 8) or to --num-callers value if this value is
smaller.
Collecting such information is expensive in both speed and
memory, particularly for programs that do many inter-thread
synchronisation events (locks, unlocks, etc). Without such
information, it is more difficult to track down the root
causes of races. Nonetheless, you may not need it in
situations where you just want to check for the presence or
absence of races, for example, when doing regression testing
of a previously race-free program.
--history-level=none is the opposite extreme. It causes
Helgrind not to collect any information about previous
accesses. This can be dramatically faster than
--history-level=full.
--history-level=approx provides a compromise between these two
extremes. It causes Helgrind to show a full trace for the
later access, and approximate information regarding the
earlier access. This approximate information consists of two
stacks, and the earlier access is guaranteed to have occurred
somewhere between program points denoted by the two stacks.
This is not as useful as showing the exact stack for the
previous access (as --history-level=full does), but it is
better than nothing, and it is almost as fast as
--history-level=none.
--history-backtrace-size=<number> [default: 8]
When --history-level=full is selected,
--history-backtrace-size=number indicates how many entries to
record in "old" accesses stack traces.
--delta-stacktrace=no|yes [default: yes on linux amd64/x86]
This flag only has any effect at --history-level=full.
--delta-stacktrace configures the way Helgrind captures the
stacktraces for the option --history-level=full. Such a
stacktrace is typically needed each time a new piece of memory
is read or written in a basic block of instructions.
--delta-stacktrace=no causes Helgrind to compute a full
history stacktrace from the unwind info each time a stacktrace
is needed.
--delta-stacktrace=yes indicates to Helgrind to derive a new
stacktrace from the previous stacktrace, as long as there was
no call instruction, no return instruction, or any other
instruction changing the call stack since the previous
stacktrace was captured. If no such instruction was executed,
the new stacktrace can be derived from the previous stacktrace
by just changing the top frame to the current program counter.
This option can speed up Helgrind by 25% when using
--history-level=full.
The following aspects have to be considered when using
--delta-stacktrace=yes :
• In some cases (for example in a function prologue), the
valgrind unwinder might not properly unwind the stack, due
to some limitations and/or due to wrong unwind info. When
using --delta-stacktrace=yes, the wrong stack trace
captured in the function prologue will be kept till the
next call or return.
• On the other hand, --delta-stacktrace=yes sometimes helps
to obtain a correct stacktrace, for example when the
unwind info allows a correct stacktrace to be done in the
beginning of the sequence, but not later on in the
instruction sequence.
• Determining which instructions are changing the callstack
is partially based on platform dependent heuristics, which
have to be tuned/validated specifically for the platform.
Also, unwinding in a function prologue must be good enough
to allow using --delta-stacktrace=yes. Currently, the
option --delta-stacktrace=yes has been reasonably
validated only on linux x86 32 bits and linux amd64 64
bits. For more details about how to validate
--delta-stacktrace=yes, see debug option --hg-sanity-flags
and the function check_cached_rcec_ok in libhb_core.c.
--conflict-cache-size=N [default: 1000000]
This flag only has any effect at --history-level=full.
Information about "old" conflicting accesses is stored in a
cache of limited size, with LRU-style management. This is
necessary because it isn't practical to store a stack trace
for every single memory access made by the program. Historical
information on not recently accessed locations is periodically
discarded, to free up space in the cache.
This option controls the size of the cache, in terms of the
number of different memory addresses for which conflicting
access information is stored. If you find that Helgrind is
showing race errors with only one stack instead of the
expected two stacks, try increasing this value.
The minimum value is 10,000 and the maximum is 30,000,000
(thirty times the default value). Increasing the value by 1
increases Helgrind's memory requirement by very roughly 100
bytes, so the maximum value will easily eat up three extra
gigabytes or so of memory.
--check-stack-refs=no|yes [default: yes]
By default Helgrind checks all data memory accesses made by
your program. This flag enables you to skip checking for
accesses to thread stacks (local variables). This can improve
performance, but comes at the cost of missing races on
stack-allocated data.
--ignore-thread-creation=<yes|no> [default: no]
Controls whether all activities during thread creation should
be ignored. By default enabled only on Solaris. Solaris
provides higher throughput, parallelism and scalability than
other operating systems, at the cost of more fine-grained
locking activity. This means for example that when a thread is
created under glibc, just one big lock is used for all thread
setup. Solaris libc uses several fine-grained locks and the
creator thread resumes its activities as soon as possible,
leaving for example stack and TLS setup sequence to the
created thread. This situation confuses Helgrind as it assumes
there is some false ordering in place between creator and
created thread; and therefore many types of race conditions in
the application would not be reported. To prevent such false
ordering, this command line option is set to yes by default on
Solaris. All activity (loads, stores, client requests) is
therefore ignored during:
• pthread_create() call in the creator thread
• thread creation phase (stack and TLS setup) in the created
thread
Also new memory allocated during thread creation is untracked,
that is race reporting is suppressed there. DRD does the same
thing implicitly. This is necessary because Solaris libc
caches many objects and reuses them for different threads and
that confuses Helgrind.
--check-stack-var=<yes|no> [default: no]
Controls whether DRD detects data races on stack variables.
Verifying stack variables is disabled by default because most
programs do not share stack variables over threads.
--exclusive-threshold=<n> [default: off]
Print an error message if any mutex or writer lock has been
held longer than the time specified in milliseconds. This
option enables the detection of lock contention.
--join-list-vol=<n> [default: 10]
Data races that occur between a statement at the end of one
thread and another thread can be missed if memory access
information is discarded immediately after a thread has been
joined. This option allows one to specify for how many joined
threads memory access information should be retained.
--first-race-only=<yes|no> [default: no]
Whether to report only the first data race that has been
detected on a memory location or all data races that have been
detected on a memory location.
--free-is-write=<yes|no> [default: no]
Whether to report races between accessing memory and freeing
memory. Enabling this option may cause DRD to run slightly
slower. Notes:
• Don't enable this option when using custom memory
allocators that use the VG_USERREQ__MALLOCLIKE_BLOCK and
VG_USERREQ__FREELIKE_BLOCK because that would result in
false positives.
• Don't enable this option when using reference-counted
objects because that will result in false positives, even
when that code has been annotated properly with
ANNOTATE_HAPPENS_BEFORE and ANNOTATE_HAPPENS_AFTER. See
e.g. the output of the following command for an example:
valgrind --tool=drd --free-is-write=yes
drd/tests/annotate_smart_pointer.
--report-signal-unlocked=<yes|no> [default: yes]
Whether to report calls to pthread_cond_signal and
pthread_cond_broadcast where the mutex associated with the
signal through pthread_cond_wait or pthread_cond_timed_waitis
not locked at the time the signal is sent. Sending a signal
without holding a lock on the associated mutex is a common
programming error which can cause subtle race conditions and
unpredictable behavior. There exist some uncommon
synchronization patterns however where it is safe to send a
signal without holding a lock on the associated mutex.
--segment-merging=<yes|no> [default: yes]
Controls segment merging. Segment merging is an algorithm to
limit memory usage of the data race detection algorithm.
Disabling segment merging may improve the accuracy of the
so-called 'other segments' displayed in race reports but can
also trigger an out of memory error.
--segment-merging-interval=<n> [default: 10]
Perform segment merging only after the specified number of new
segments have been created. This is an advanced configuration
option that allows one to choose whether to minimize DRD's
memory usage by choosing a low value or to let DRD run faster
by choosing a slightly higher value. The optimal value for
this parameter depends on the program being analyzed. The
default value works well for most programs.
--shared-threshold=<n> [default: off]
Print an error message if a reader lock has been held longer
than the specified time (in milliseconds). This option enables
the detection of lock contention.
--show-confl-seg=<yes|no> [default: yes]
Show conflicting segments in race reports. Since this
information can help to find the cause of a data race, this
option is enabled by default. Disabling this option makes the
output of DRD more compact.
--show-stack-usage=<yes|no> [default: no]
Print stack usage at thread exit time. When a program creates
a large number of threads it becomes important to limit the
amount of virtual memory allocated for thread stacks. This
option makes it possible to observe how much stack memory has
been used by each thread of the client program. Note: the DRD
tool itself allocates some temporary data on the client thread
stack. The space necessary for this temporary data must be
allocated by the client program when it allocates stack
memory, but is not included in stack usage reported by DRD.
--ignore-thread-creation=<yes|no> [default: no]
Controls whether all activities during thread creation should
be ignored. By default enabled only on Solaris. Solaris
provides higher throughput, parallelism and scalability than
other operating systems, at the cost of more fine-grained
locking activity. This means for example that when a thread is
created under glibc, just one big lock is used for all thread
setup. Solaris libc uses several fine-grained locks and the
creator thread resumes its activities as soon as possible,
leaving for example stack and TLS setup sequence to the
created thread. This situation confuses DRD as it assumes
there is some false ordering in place between creator and
created thread; and therefore many types of race conditions in
the application would not be reported. To prevent such false
ordering, this command line option is set to yes by default on
Solaris. All activity (loads, stores, client requests) is
therefore ignored during:
• pthread_create() call in the creator thread
• thread creation phase (stack and TLS setup) in the created
thread
--trace-addr=<address> [default: none]
Trace all load and store activity for the specified address.
This option may be specified more than once.
--ptrace-addr=<address> [default: none]
Trace all load and store activity for the specified address
and keep doing that even after the memory at that address has
been freed and reallocated.
--trace-alloc=<yes|no> [default: no]
Trace all memory allocations and deallocations. May produce a
huge amount of output.
--trace-barrier=<yes|no> [default: no]
Trace all barrier activity.
--trace-cond=<yes|no> [default: no]
Trace all condition variable activity.
--trace-fork-join=<yes|no> [default: no]
Trace all thread creation and all thread termination events.
--trace-hb=<yes|no> [default: no]
Trace execution of the ANNOTATE_HAPPENS_BEFORE(),
ANNOTATE_HAPPENS_AFTER() and ANNOTATE_HAPPENS_DONE() client
requests.
--trace-mutex=<yes|no> [default: no]
Trace all mutex activity.
--trace-rwlock=<yes|no> [default: no]
Trace all reader-writer lock activity.
--trace-semaphore=<yes|no> [default: no]
Trace all semaphore activity.
--heap=<yes|no> [default: yes]
Specifies whether heap profiling should be done.
--heap-admin=<size> [default: 8]
If heap profiling is enabled, gives the number of
administrative bytes per block to use. This should be an
estimate of the average, since it may vary. For example, the
allocator used by glibc on Linux requires somewhere between 4
to 15 bytes per block, depending on various factors. That
allocator also requires admin space for freed blocks, but
Massif cannot account for this.
--stacks=<yes|no> [default: no]
Specifies whether stack profiling should be done. This option
slows Massif down greatly, and so is off by default. Note that
Massif assumes that the main stack has size zero at start-up.
This is not true, but doing otherwise accurately is difficult.
Furthermore, starting at zero better indicates the size of the
part of the main stack that a user program actually has
control over.
If you give at least 4 -v verbosity arguments, then massif
produces a trace for each stack increase and decrease. The
stack increase trace contains the IP address that increased
the stack. Note that to get fully precise IP address, you must
specify the options -px-default=unwindregs-at-mem-access
--px-file-backed=unwindregs-at-mem-access.
--pages-as-heap=<yes|no> [default: no]
Tells Massif to profile memory at the page level rather than
at the malloc'd block level. See above for details.
--depth=<number> [default: 30]
Maximum depth of the allocation trees recorded for detailed
snapshots. Increasing it will make Massif run somewhat more
slowly, use more memory, and produce bigger output files.
--alloc-fn=<name>
Functions specified with this option will be treated as though
they were a heap allocation function such as malloc. This is
useful for functions that are wrappers to malloc or new, which
can fill up the allocation trees with uninteresting
information. This option can be specified multiple times on
the command line, to name multiple functions.
Note that the named function will only be treated this way if
it is the top entry in a stack trace, or just below another
function treated this way. For example, if you have a function
malloc1 that wraps malloc, and malloc2 that wraps malloc1,
just specifying --alloc-fn=malloc2 will have no effect. You
need to specify --alloc-fn=malloc1 as well. This is a little
inconvenient, but the reason is that checking for allocation
functions is slow, and it saves a lot of time if Massif can
stop looking through the stack trace entries as soon as it
finds one that doesn't match rather than having to continue
through all the entries.
Note that C++ names are demangled. Note also that overloaded
C++ names must be written in full. Single quotes may be
necessary to prevent the shell from breaking them up. For
example:
--alloc-fn='operator new(unsigned, std::nothrow_t const&)'
Arguments of type size_t need to be replaced with unsigned
long on 64bit platforms and unsigned on 32bit platforms.
--alloc-fn will work with inline functions. Inline function
names are not mangled, which means that you only need to
provide the function name and not the argument list.
--alloc-fn does not support wildcards.
--ignore-fn=<name>
Any direct heap allocation (i.e. a call to malloc, new, etc,
or a call to a function named by an --alloc-fn option) that
occurs in a function specified by this option will be ignored.
This is mostly useful for testing purposes. This option can be
specified multiple times on the command line, to name multiple
functions.
Any realloc of an ignored block will also be ignored, even if
the realloc call does not occur in an ignored function. This
avoids the possibility of negative heap sizes if ignored
blocks are shrunk with realloc.
The rules for writing C++ function names are the same as for
--alloc-fn above.
--threshold=<m.n> [default: 1.0]
The significance threshold for heap allocations, as a
percentage of total memory size. Allocation tree entries that
account for less than this will be aggregated. Note that this
should be specified in tandem with ms_print's option of the
same name.
--peak-inaccuracy=<m.n> [default: 1.0]
Massif does not necessarily record the actual global memory
allocation peak; by default it records a peak only when the
global memory allocation size exceeds the previous peak by at
least 1.0%. This is because there can be many local allocation
peaks along the way, and doing a detailed snapshot for every
one would be expensive and wasteful, as all but one of them
will be later discarded. This inaccuracy can be changed (even
to 0.0%) via this option, but Massif will run drastically
slower as the number approaches zero.
--time-unit=<i|ms|B> [default: i]
The time unit used for the profiling. There are three
possibilities: instructions executed (i), which is good for
most cases; real (wallclock) time (ms, i.e. milliseconds),
which is sometimes useful; and bytes allocated/deallocated on
the heap and/or stack (B), which is useful for very short-run
programs, and for testing purposes, because it is the most
reproducible across different machines.
--detailed-freq=<n> [default: 10]
Frequency of detailed snapshots. With --detailed-freq=1, every
snapshot is detailed.
--max-snapshots=<n> [default: 100]
The maximum number of snapshots recorded. If set to N, for all
programs except very short-running ones, the final number of
snapshots will be between N/2 and N.
--massif-out-file=<file> [default: massif.out.%p]
Write the profile data to file rather than to the default
output file, massif.out.<pid>. The %p and %q format specifiers
can be used to embed the process ID and/or the contents of an
environment variable in the name, as is the case for the core
option --log-file.
--bb-out-file=<name> [default: bb.out.%p]
This option selects the name of the basic block vector file.
The %p and %q format specifiers can be used to embed the
process ID and/or the contents of an environment variable in
the name, as is the case for the core option --log-file.
--pc-out-file=<name> [default: pc.out.%p]
This option selects the name of the PC file. This file holds
program counter addresses and function name info for the
various basic blocks. This can be used in conjunction with the
basic block vector file to fast-forward via function names
instead of just instruction counts. The %p and %q format
specifiers can be used to embed the process ID and/or the
contents of an environment variable in the name, as is the
case for the core option --log-file.
--interval-size=<number> [default: 100000000]
This option selects the size of the interval to use. The
default is 100 million instructions, which is a commonly used
value. Other sizes can be used; smaller intervals can help
programs with finer-grained phases. However smaller interval
size can lead to accuracy issues due to warm-up effects (When
fast-forwarding the various architectural features will be
un-initialized, and it will take some number of instructions
before they "warm up" to the state a full simulation would be
at without the fast-forwarding. Large interval sizes tend to
mitigate this.)
--instr-count-only [default: no]
This option tells the tool to only display instruction count
totals, and to not generate the actual basic block vector
file. This is useful for debugging, and for gathering
instruction count info without generating the large basic
block vector files.
--basic-counts=<no|yes> [default: yes]
When enabled, Lackey prints the following statistics and
information about the execution of the client program:
1. The number of calls to the function specified by the
--fnname option (the default is main). If the program has
had its symbols stripped, the count will always be zero.
2. The number of conditional branches encountered and the
number and proportion of those taken.
3. The number of superblocks entered and completed by the
program. Note that due to optimisations done by the JIT,
this is not at all an accurate value.
4. The number of guest (x86, amd64, ppc, etc.) instructions
and IR statements executed. IR is Valgrind's RISC-like
intermediate representation via which all instrumentation
is done.
5. Ratios between some of these counts.
6. The exit code of the client program.
--detailed-counts=<no|yes> [default: no]
When enabled, Lackey prints a table containing counts of
loads, stores and ALU operations, differentiated by their IR
types. The IR types are identified by their IR name ("I1",
"I8", ... "I128", "F32", "F64", and "V128").
--trace-mem=<no|yes> [default: no]
When enabled, Lackey prints the size and address of almost
every memory access made by the program. See the comments at
the top of the file lackey/lk_main.c for details about the
output format, how it works, and inaccuracies in the address
trace. Note that this option produces immense amounts of
output.
--trace-superblocks=<no|yes> [default: no]
When enabled, Lackey prints out the address of every
superblock (a single entry, multiple exit, linear chunk of
code) executed by the program. This is primarily of interest
to Valgrind developers. See the comments at the top of the
file lackey/lk_main.c for details about the output format.
Note that this option produces large amounts of output.
--fnname=<name> [default: main]
Changes the function for which calls are counted when
--basic-counts=yes is specified.
Valgrind supports the downloading of debuginfo files via
debuginfod, an HTTP server for distributing ELF/DWARF debugging
information. When a debuginfo file cannot be found locally,
Valgrind is able to query debuginfod servers for the file using
the file's build-id.
In order to use this feature debuginfod-find must be installed and
the $DEBUGINFOD_URLS environment variable must contain
space-separated URLs of debuginfod servers. Valgrind does not
support debuginfod-find verbose output that is normally enabled
with $DEBUGINFOD_PROGRESS and $DEBUGINFOD_VERBOSE. These
environment variables will be ignored. This feature is supported
on Linux only.
For more information regarding debuginfod, see Elfutils
Debuginfod[1] .
cg_annotate(1), callgrind_annotate(1), callgrind_control(1),
ms_print(1), $INSTALL/share/doc/valgrind/html/index.html or
http://www.valgrind.org/docs/manual/index.html, Debugging your
program using Valgrind's gdbserver and GDB[2] vgdb[3], Valgrind
monitor commands[4], The Commentary[5], Scheduling and
Multi-Thread Performance[6], Cachegrind: a cache and
branch-prediction profiler[7]. Execution Trees[8]
See the AUTHORS file in the valgrind distribution for a
comprehensive list of authors.
This manpage was written by Andres Roldan <aroldan@debian.org> and
the Valgrind developers.
1. Elfutils Debuginfod
https://sourceware.org/elfutils/Debuginfod.html
2. Debugging your program using Valgrind's gdbserver and GDB
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.gdbserver
3. vgdb
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.vgdb
4. Valgrind monitor commands
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.valgrind-monitor-commands
5. The Commentary
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.comment
6. Scheduling and Multi-Thread Performance
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.pthreads_perf_sched
7. Cachegrind: a cache and branch-prediction profiler
http://www.valgrind.org/docs/manual/cg-manual.html
8. Execution Trees
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.xtree
This page is part of the valgrind (a system for debugging and
profiling Linux programs) project. Information about the project
can be found at ⟨http://www.valgrind.org/⟩. If you have a bug
report for this manual page, see
⟨http://www.valgrind.org/support/bug_reports.html⟩. This page was
obtained from the project's upstream Git repository
⟨http://sourceware.org/git/valgrind.git⟩ on 2025-02-02. (At that
time, the date of the most recent commit that was found in the
repository was 2025-01-28.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
Release 3.25.0.GIT 02/02/2025 VALGRIND(1)
Pages that refer to this page: callgrind_annotate(1), callgrind_control(1), cg_annotate(1), cg_diff(1), cg_merge(1), dbpmda(1), ms_print(1), valgrind-di-server(1), valgrind-listener(1), vgdb(1), malloc(3), ovs-ctl(8)
|
HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|