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 2020-08-13.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-08-11.)  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)