SYNOPSIS

latrace [-snltfvhiBdISbcCyYLpoaNADVTFERq] command [arg … ]

DESCRIPTION

The latrace tracer is able to run a command and display its dynamic library calls using a LD_AUDIT libc feature, available from libc version 2.4 onward. It is also capable to measure and display various statistics of dynamic calls. See [DISCUSSION] for more details.

If the header file with functions' declarations is provided, latrace will display functions’s arguments. The header file file syntax is similar to the C language, with several exceptions See [HEADERS] for more details.

The latrace by default fully operates inside of the traced program. However another "pipe mode" is available to move the main work to the tracer - the latrace binary. See [PIPEMODE] for more details.

The latrace use is similar to strace(1) and ltrace(1).

OPTIONS

-l, --libs lib1[,lib2,…]

audit from and to lib1, lib2 …

-t, --libs-to lib1[,lib2,…]

audit to lib1, lib2 …

-f, --libs-from lib1[,lib2,…]

audit from lib1, lib2 …

-s, --sym sym1[,sym2,…]

audit symbols sym1, sym2 …

-n, --sym-omit sym1[,sym2,…]

omit symbols sym1, sym2 …

-L, --lib-subst s1[,s2,…]

objsearch LD_AUDIT interface (See [OBJSEARCH])

-c, --counts

display statistics counts of symbols - implies pipe mode (see [PIPEMODE]) an no symbol output is displayed

-C, --sort-counts stat

implies -c, plus sort the statistics by stat with following values: time,per,call,ucall,lib,sym (default is call)

-p, --pipe

use pipe to latrace process to send audit data (see [PIPEMODE])

-N, --conf

config file (see [CONFIG])

-A, --enable-args

enable arguments output (definitions from /etc/latrace.conf)

-D, --detail-args

display struct arguments in more detail

-a, --args file

specify arguments definition file, implies -A (without the default definition file of course)

-y, --framesize number

framesize for storing the stack before pltexit (default 100)

-Y, --no-framesize-check

disable framesize check

-F, --no-follow-fork

dont follow fork calls (childs). This is just supressing the latrace output from new childs. The nature of the LD_AUDIT feature prevents to disable it completely.

-E, --no-follow-exec

dont follow exec calls

-S, --timestamp

display timestamp for each symbol

-b, --flow-below sym1[,sym2,…]

display flow for sym1, sym2 …

-I, --no-indent-sym

do no indent symbols based on the their stack depth

-i, --indent-sym indent_size

indent size specification in indent_size

-B, --braces

allways display { } for the around the symbol body

-d, --demangle

C++ demangle symbols on the output

-T, --hide-tid

dont display thread id

-o, --output file

store output to file

-R, --ctl-config

controled config feature

-q, --disable

run with disabled auditing

-v, --verbose

verbose output

-V, --version

display version

-h, --help

display help

EXAMPLES

DISCUSSION

NAMES CHECK

For options "-l -t -f -s -n -b" the * symbol can be used to switch to the substring search. If it is not specified, the exact search for the name is done.

Examples:

-s "*krava" checks for symbols with "krava" substring.
-s "krava"  checks only for "krava" symbol

LD_AUDIT

This is just a brief and vague description of the LD_AUDIT feature. For more information look to rtld-audit(7) man done by Petr Baudis or study the glibc/latrace source code. Very brief explanation follows.

The libc dynamic linker audit feature allows to trace/audit program’s symbols/libraries. The feature is enabled by the LD_AUDIT environment variable. This variable must contain path to the audit shared library. This audit library needs to follow specific interface. The interface functions will be then called by the dynamic linker appropriatelly.

The audit library needs to export following symbols (the "la_PLTENTER" and "la_PLTEXIT" names are architecture dependent).

"la_activity"
"la_objsearch"
"la_objopen"
"la_preinit"
"la_symbind32"
"la_symbind64"
"la_PLTENTER"
"la_PLTEXIT"
"la_objclose"

As for the latrace package the audit shared library is called libltaudit.so.

OBJSEARCH

The objsearch LD_AUDIT interface provide means for changing traced program shared object names/locations. The -L option argument should have following form:

-L s1[,s2,…] where sN is src [=%~] dst

The src is the source pattern/name and dst is the destination name/pattern.

=

Comparing src with the library name. If matched, replace the library name with dst.

library name         - /lib/krava1.so
src                  - /lib/krava1.so
dst                  - /lib/krava2.so
final library name   - /lib/krava2.so
%

Looking for the src in the library name. If found, replace the src with dst part.

library name         - /lib/krava1.so
src                  - krava1
dst                  - krava2
final library name   - /lib/krava2.so
~

Looking for the src in the library name. If found, replace the library name with dst.

library name         - /lib/krava1.so
src                  - krava1
dst                  - /lib/krava2.so
final library name   - /lib/krava2.so

PIPE mode

The latrace can work in two modes. The first one native does does the output directly in the traced program process. The other one, pipe mode use the IPC fifo mechanism to send the data from the traced process to the latrace process. The latrace process is then responsible for the output. Using the pipe mode you loose the traced program standard output context with printed symbols.

By using the pipe mode, the latrace is not dependent on the trace program usage/manipulation of the standard output descriptor. Also the symbol statistics counts -c, -C options use the pipe mode to transfer symbol information to the latrace binary, and the latrace binary does the counts at the end.

CONFIG

The latrace provide possibility to enable/disable some of the options by means of configuration file. Some of the options are linked to the command line arguments some of them are not. When latrace starts the global configuration file is read. This file is usually being placed in here:

/etc/latrace.d/latrace.conf

Having default values read from this file, user can overload any of them by command line options or by supling another config file via -N, --conf option.

The configuration file syntax is roughly:

INCLUDE <anotherconfigfile>

OPTIONS {
        OPTION1 = VALUE
        OPTION2 = YES|NO
        ...
        OPTIONN = VALUE
}

# comment

Configuration file options

HEADERS = FILE

-a, --args

INDENT_SYM = VALUE

-i, --indent-sym

PIPE = BOOL

-p, --pipe

TIMESTAMP = BOOL

-S, --timestamp

FRAMESIZE = VALUE

-y, --framesize

FRAMESIZE_CHECK = BOOL

-Y, --no-framesize-check

HIDE_TID = BOOL

-T, --hide-tid

FOLLOW_FORK = BOOL

-F, --no-follow-fork

FOLLOW_EXEC = BOOL

-E, --no-follow-exec

DEMANGLE = BOOL

-d, --demangle

BRACES = BOOL

-B, --braces

ENABLE_ARGS = BOOL

-A, --enable-args

DETAIL_ARGS = BOOL

-D, --detail-args

OUTPUT_TTY = FILE
  • stores tracee terminal output to the file

LIBS = LIB1[,LIB2,…]

-l, --libs

LIBS_TO = LIB1[,LIB2,…]

-t, --libs-to

LIBS_FROM = LIB1[,LIB2,…]

-f, --libs-from

SYM = SYM1[,SYM2,…]

-s, --sym

SYM_OMIT = SYM1[,SYM2,…]

-n, --sym-omit

SYM_BELOW = SYM1[,SYM2,…]

-b, --flow-below

SYM_NOEXIT = SYM1[,SYM2,…]
  • symbols which do no run exit callback (plt_exit)

ARGS_STRING_POINTER_LENGTH = BOOL
  • function arguments - display string length and pointer value

HEADERS

The latrace header file allows user to define symbols as an classic C functions with arguments. Argument names will be displayed together with values as the latrace output. The more arguments are defined, the more performance and memory penalties should be expected.

The package is delivered with several predefined header files for the most commonly used functions. List of the glibc header files used follows (the list mostly follows the ltrace header files list, and author is willing to update it according to the needs)

ctype.h dirent.h dlfcn.h fcntl.h getopt.h inet.h ioctl.h
libintl.h libio.h locale.h misc.h mman.h ncurses.h netdb.h
pthread.h pwd.h resource.h signal.h socket.h stat.h stdio.h
stdlib.h string.h syslog.h term.h termios.h time.h typedefs.h
unistd.h utmp.h wait.h

The latrace header files are usually stored under directory:

/etc/latrace.d/headers/

User can specify single header file using command line option or configuration file. This file then can include other needed headers. As already mentioned, the latrace config file syntax lightly follows the C language syntax. Following part describes the latrace config file language.

PORTS

The latrace should work on any glibc system with LD_AUDIT support. However arguments details are architecture specific and need special support inside latrace itself.

Author is willing to port the latrace to any architecture, as long as he got an access to corresponding system. Currently functional ports are:

x86

ok

x86_64

ok

arm

ok

BUGS

MANY, plz report bugs to <latrace@lists.fedorahosted.org> or <olsajiri@gmail.com>.

You can also visit the http://people.redhat.com/jolsa/latrace/ page to see the latest release notes information.

LD_AUDIT related glibc bugs:

AUTHOR

Jiri Olsa <olsajiri@gmail.com>

CONTRIBUTORS

LICENSE

This is free software, distributed under the GPLv3 license.

SEE ALSO

strace(1), ltrace(1)