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NAME | DESCRIPTION | INITIALIZATION PARAMETERS | PORTS | BUGS | RESOURCES | AUTHORS | COPYRIGHT | SEE ALSO | COLOPHON |
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BABELTRACE2-FILTER() BABELTRACE2-FILTER()
babeltrace2-filter.lttng-utils.debug-info - Babeltrace 2:
Debugging information filter component class for LTTng traces
A Babeltrace 2 filter.lttng-utils.debug-info message iterator
creates and emits copies of upstream messages, augmenting LTTng
event messages with debugging information when it’s available and
possible.
Messages without
debugging information
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| +----------------------------+
| | flt.lttng-utils.debug-info |
| | |
'->@ in out @--> Messages with
+----------------------------+ debugging information
See babeltrace2-intro(7) to learn more about the Babeltrace 2
project and its core concepts.
A filter.lttng-utils.debug-info message iterator uses the LTTng
state dump events as well as the ip (instruction pointer) and vpid
(process ID) common context fields of the event to locate and read
the corresponding debugging information. The message iterator can
find the extra debugging information in an executable file or in a
directory containing debugging information which the compiler
creates.
The new LTTng events (copies of the original ones with added
debugging information) contain, when possible, a new event common
context structure field (besides the ip field) named debug_info by
default (you can use the debug-info-field-name parameter to choose
another name). This structure field contains the following fields:
bin [string]
Executable path or name followed with @ADDR or +ADDR, where
ADDR is the address (hexadecimal) where it was loaded while
being traced.
@ADDR means ADDR is an absolute address, and +ADDR means ADDR
is a relative address.
Examples: my-program@0x4b7fdd23, my-program+0x18d7c.
func [string]
Function name followed with +OFFSET, where OFFSET is the
offset (hexadecimal) from the beginning of the function symbol
in the executable file.
Example: load_user_config+0x194.
src [string]
Source file path or name followed with :LINE, where LINE is
the line number in this source file at which the event
occurred.
Example: user-config.c:1025.
Any of the previous fields can be an empty string if the debugging
information was not available for the analyzed original LTTng
event.
A filter.lttng-utils.debug-info message iterator systematically
copies the upstream messages, but it only augments compatible
LTTng event classes. This means that the message iterator copies
messages of non-LTTng trace (see “LTTng prerequisites”) without
alteration.
Compile an executable for debugging information analysis
With GCC or Clang, you need to compile the program or library
source files in debug mode with the -g option. This option makes
the compiler generate debugging information in the native format
of the operating system. This format is recognized by a
filter.lttng-utils.debug-info component: it can translate the
instruction pointer field of an event common context to a source
file and line number, along with the name of the surrounding
function.
Important
This component class only supports the debugging information
in DWARF format, version 2 or later. Use the -gdwarf or
-gdwarf-VERSION (where VERSION is the DWARF version) compiler
options to explicitly generate DWARF debugging information.
If you don’t compile the source files of the executable with the
-g option or with an equivalent option, then no DWARF information
is available: the message iterator uses ELF symbols from the
executable file instead. In this case, the events that the message
iterator creates don’t contain the source file and line number
(see the src field), but only the name of the nearest function
symbol with an offset in bytes to the location in the executable
from which the LTTng event occurred (see the func field).
If the executable file has neither ELF symbols nor DWARF
information, then the filter.lttng-utils.debug-info message
iterator cannot map the event to its source location: the message
iterator still copies the upstream messages but without altering
them.
LTTng prerequisites
A filter.lttng-utils.debug-info message iterator can only analyze
user space events which LTTng (see <https://lttng.org>) 2.8.0 or
later generates.
To get debugging information for LTTng-UST events which occur in
executables and libraries which the system loader loads (what you
can see with ldd(1)):
1. Add the ip and vpid context fields to user space event
records:
$ lttng add-context --userspace --type=ip --type=vpid
See lttng-add-context(1) for more details.
2. Enable the LTTng-UST state dump events:
$ lttng enable-event --userspace 'lttng_ust_statedump:*'
See lttng-enable-event(1) and lttng-ust(3) for more details.
To get debugging information for LTTng-UST events which occur in
dynamically loaded objects, for example plugins:
1. Do the previous steps (add context fields and enable the
LTTng-UST state dump events).
2. Enable the LTTng-UST dynamic linker tracing helper events:
$ lttng enable-event --userspace 'lttng_ust_dl:*'
See lttng-ust-dl(3) for more details.
3. When you are ready to trace, start your application with the
LD_PRELOAD environment variable set to liblttng-ust-dl.so:
$ LD_PRELOAD=liblttng-ust-dl.so my-app
Separate debugging information
You can store DWARF debugging information outside the executable
itself, whether it’s to reduce the file size of the executable or
simply to facilitate sharing the debugging information.
This is usually achieved via one of two mechanisms, namely build
ID and debug link. Their use and operation is described in the
Debugging Information in Separate Files (see
<https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-
Files.html>) section of GDB’s documentation.
A filter.lttng-utils.debug-info message iterator can find separate
debugging information files automatically, as long as they meet
the requirements stated in this manual page.
The debugging information lookup order is the same as GDB’s,
namely:
1. Within the executable file itself.
2. Through the build ID method in the /usr/lib/debug/.build-id
directory.
3. In the various possible debug link locations.
The message iterator uses the first debugging information file
that it finds.
You can use the debug-info-dir initialization parameter to
override the default /usr/lib/debug directory used in the build ID
and debug link methods.
Note
It’s currently not possible to make this component search for
debugging information in multiple directories.
Target prefix
The debugging information analysis that a filter.lttng-
utils.debug-info message iterator performs uses the paths to the
executables as collected during tracing as the default mechanism
to resolve DWARF and ELF information.
If the trace was recorded on a separate machine, however, then you
can use the target-prefix parameter to specify a prefix directory,
that is, the root of the target file system.
For example, if the path of an instrumented executable is
/usr/bin/foo on the target system, then you can place this file at
/home/user/target/usr/bin/foo on the system on which you use a
filter.lttng-utils.debug-info component. In this case, the target
prefix to use is /home/user/target.
debug-info-dir=DIR [optional string]
Use DIR as the directory from which to load debugging
information with the build ID and debug link methods instead
of /usr/lib/debug.
debug-info-field-name=NAME [optional string]
Name the debugging information structure field in the common
context of the created events NAME instead of the default
debug_info.
full-path=VAL [optional boolean]
If VAL is true, then use the full path when writing the
executable name (bin) and source file name (src) fields in the
debug_info context field of the created events.
Default: false.
target-prefix=DIR [optional string]
Use DIR as the root directory of the target file system
instead of /.
+----------------------------+
| flt.lttng-utils.debug-info |
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@ in out @
+----------------------------+
Input
in
Single input port.
Output
out
Single output port.
If you encounter any issue or usability problem, please report it
on the Babeltrace bug tracker (see
<https://bugs.lttng.org/projects/babeltrace>).
The Babeltrace project shares some communication channels with the
LTTng project (see <https://lttng.org/>).
• Babeltrace website (see <https://babeltrace.org/>)
• Mailing list (see <https://lists.lttng.org>) for support and
development: lttng-dev@lists.lttng.org
• IRC channel (see <irc://irc.oftc.net/lttng>): #lttng on
irc.oftc.net
• Bug tracker (see <https://bugs.lttng.org/projects/babeltrace>)
• Git repository (see
<https://git.efficios.com/?p=babeltrace.git>)
• GitHub project (see <https://github.com/efficios/babeltrace>)
• Continuous integration (see
<https://ci.lttng.org/view/Babeltrace/>)
• Code review (see
<https://review.lttng.org/q/project:babeltrace>)
The Babeltrace 2 project is the result of hard work by many
regular developers and occasional contributors.
The current project maintainer is Jérémie Galarneau
<mailto:jeremie.galarneau@efficios.com>.
This component class is part of the Babeltrace 2 project.
Babeltrace is distributed under the MIT license (see
<https://opensource.org/licenses/MIT>).
babeltrace2-intro(7), babeltrace2-plugin-lttng-utils(7), lttng(1),
lttng-add-context(1)
This page is part of the babeltrace (trace read and write
libraries and a trace converter) project. Information about the
project can be found at ⟨http://www.efficios.com/babeltrace⟩. If
you have a bug report for this manual page, send it to
lttng-dev@lists.lttng.org. This page was obtained from the
project's upstream Git repository
⟨git://git.efficios.com/babeltrace.git⟩ on 2025-02-02. (At that
time, the date of the most recent commit that was found in the
repository was 2025-01-24.) 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
BABELTRACE2-FILTER()
Pages that refer to this page: babeltrace2(1), babeltrace2-convert(1), babeltrace2-plugin-lttng-utils(7)
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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. |
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