ltrace and latrace
Table of Contents
Overview
Similar to strace, which can be used to trace system calls, ltrace can be used to trace shared library calls.
Trace shared library calls with ltrace
// hello.c #include <stdio.h> void Print(const char* s) { printf("%s", s); } // hello.h void Print(const char* s); // hello_main.c #include "hello.h" int main() { Print("Hello World\n"); return 0; }
makefile
all:
gcc -fPIC --shared -o libhello.so hello.c
gcc -o hello hello_main.c -lhello -L.
Use ltrace to see which library calls are called:
$ export LD_LIBRARY_PATH=. $ ltrace ./hello __libc_start_main(0x804852c, 1, 0xbfbc7864, 0x8048550, 0x80485c0 <unfinished ...> Print(0x80485e8, 0, 0x8048559, 0xb7722ff4, 0x8048550Hello World ) = 12 +++ exited (status 0) +++
One drawback with ltrace is that it only traces calls from the executable to the libraries the executable is linked against - it does not trace calls between libraries.
Trace shared library calls with latrace
On Ubuntu, it can be installed with
$ sudo apt-get install latrace
- latrace also traces library calls between shared libraries, so the
output includes the
printfcall executed from our own shared library. - the shared library name which contains the symbol is printed after each function call:
$ latrace ./hello
6432 __libc_start_main [/lib/i386-linux-gnu/libc.so.6]
6432 Print [./libhello.so]
Hello World
6432 printf [/lib/i386-linux-gnu/libc.so.6]
6432 free [/lib/i386-linux-gnu/libc.so.6]
6432 free [/lib/i386-linux-gnu/libc.so.6]
6432 __cxa_finalize [/lib/i386-linux-gnu/libc.so.6]
./hello finished - exited, status=0