babeltrace2-filter.lttng-utils.debug-info(7) — Linux manual page

NAME | DESCRIPTION | INITIALIZATION PARAMETERS | PORTS | BUGS | RESOURCES | AUTHORS | COPYRIGHT | SEE ALSO | COLOPHON

BABELTRACE2-FILTER()                                BABELTRACE2-FILTER()

NAME         top

       babeltrace2-filter.lttng-utils.debug-info - Babeltrace 2's
       debugging information filter component class for LTTng traces

DESCRIPTION         top

       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
             |
             |  +----------------------------+
             |  | 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 event common context’s ip
       (instruction pointer) and vpid (process ID) fields 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’s 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 operating
       system’s native format. This format is recognized by a
       filter.lttng-utils.debug-info component: it can translate the
       instruction pointer field of an event’s 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 executable’s source files with the -g
       option or with an equivalent option, 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 do not 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, 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’s 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 is to reduce the executable’s file size 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 is 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, you can
       use the target-prefix parameter to specify a prefix directory,
       that is, the root of the target file system.

       For example, if an instrumented executable’s path is /usr/bin/foo
       on the target system, 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.

INITIALIZATION PARAMETERS         top

       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=yes [optional boolean]
           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.

       target-prefix=DIR [optional string]
           Use DIR as the root directory of the target file system
           instead of /.

PORTS         top

           +----------------------------+
           | flt.lttng-utils.debug-info |
           |                            |
           @ in                     out @
           +----------------------------+

   Input
       in
           Single input port.

   Output
       out
           Single output port.

BUGS         top

       If you encounter any issue or usability problem, please report it
       on the Babeltrace bug tracker (see
       <https://bugs.lttng.org/projects/babeltrace>).

RESOURCES         top

       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>)

AUTHORS         top

       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>.

COPYRIGHT         top

       This component class is part of the Babeltrace 2 project.

       Babeltrace is distributed under the MIT license (see
       <https://opensource.org/licenses/MIT>).

SEE ALSO         top

       babeltrace2-intro(7), babeltrace2-plugin-lttng-utils(7),
       lttng(1), lttng-add-context(1)

COLOPHON         top

       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 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-20.)  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)