latrace - Online in the Cloud

PROGRAM:

NAME

latrace - LD_AUDIT 2.4+ libc frontend

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 the section called
“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 the section called “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 the
section called “PIPE mode” 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 the section called “OBJSEARCH”)

-c, --counts
display statistics counts of symbols - implies pipe mode (see the section called “PIPE
mode”) 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 the section called “PIPE mode”)

-N, --conf
config file (see the section called “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

· The simplest way to run latrace is like this:

latrace cat

· To see the argument values specified by default config file run:

latrace -A cat

· Same as above but using the pipe mode to get all the end symbols printed:

latrace -Ap cat

· To see the argument values specified by specified config file run:

latrace -a latrace.conf cat

· To get output only for specified symbol (eg. read and write) run:

latrace -A -s read,write cat

· To get flow under the specified symbol (eg. sysconf) run:

latrace -b sysconf kill

· To get output only for specified library (eg. libproc) run:

latrace -Al libproc w

· To get symbol statistics run:

latrace -c ls

· To get symbol statistics sorted by time run:

latrace -C time ls

· To get output stored to the text file run:

latrace -o output.latrace ls

· To change the libkrava1.so dependency to the libkrava2.so run one of these:

latrace -L krava1%krava2 ex

latrace -L krava1~libkrava2.so ex

latrace -L libkrava1.so=libkrava2.so ex

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.

· Several POD types (plain old data), are hardcoded in latrace. Size of those arguments
is determined by the sizeof macro. The list follows.

void
char u_char
short u_short
int u_int
long u_long
llong u_llong # (long long)
float double

· The typedef keyword allows to specify new type based on the already existing one (POD
or typedefed). Eventhough there’s a way for multiple pointer layers in the type
definition (*), only one is taken.

typedef base_type new_type;
typedef base_type * new_type;
typedef base_type ** new_type;

· Comments follow the C style /\* \*/ logic.

/\* comments \*/

· The include keyword allows to include another config file.

#include "filename"

· The struct keyword allows to define the structure. The syntax folows following grammar
rules.

START:: struct NAME { STRUCT_DEF };
STRUCT_DEF:: DEF | EMPTY
DEF:: NAME NAME |
NAME '*' NAME |
struct NAME NAME |
struct NAME '*' NAME
NAME:: [-0-9a-zA-Z_]+

· The function definition follows following syntax (DEF and NAME are the same as for
struct definition).

START:: DEF '(' ARGS ')' ';'
ARGS:: ARGS ',' DEF | DEF | EMPTY

· The enum definition follows following syntax (NAME is same as for struct definition).

START:: ENUM NAME '{' ENUM_DEF '}' ';'
ENUM_DEF:: ENUM_DEF ',' ENUM_ELEM | ENUM_ELEM
ENUM_ELEM:: NAME '=' NAME | NAME

· Example of a simple latrace config file.

---[ cut here ]-----------------------------
enum krava {
krava1 = 1,
krava2,
krava3 = 100
};

#include "krava.conf"

typedef u_int pid_t;

struct ex_st {
pid_t p;
int cnt;
char *name;
};

int f1(pid_t p, struct ex_st *k);
int f2(char* name, struct ex_st k, int k = krava);
struct ex_st* f3(pid_t *p, struct ex_st k);
---[ cut here ]-----------------------------

· Arrays are not supported yet, so there’s no way to define some structures. For such a
structures use void* type where the structure argu- ment is passed by pointer. If it
is passed by value, there’s no workaround so far (aside from filling the structure
body with POD types up to the actual length of the structure :).

· Variable argument lists (va_list/...) are not supported yet. The function definition
needs to stop before the first variable argument list argument.

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

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