I have a C program using dynamically loaded library to load plugins. I would like to trace the library calls in order to debug the plugin's loading.
I looked at ltrace, but I can't seem to make it work:
Here is an example program:
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
int main() {
int *a = malloc(sizeof(int));
void *handle;
double (*cosine)(double);
char *error;
handle = dlopen ("/usr/lib/x86_64-linux-gnu/libm.so.6", RTLD_LAZY);
if (!handle) {
fputs (dlerror(), stderr);
exit(1);
}
cosine = dlsym(handle, "cos");
if ((error = dlerror()) != NULL) {
fputs(error, stderr);
exit(1);
}
printf ("%f\n", (*cosine)(2.0));
dlclose(handle);
return 0;
}
Compiling (and removing PIE, otherwise ltrace won't see anything):
gcc main.c -pg -ldl -no-pie
Running: ltrace ./a.out
Output
__monstartup(0x401170, 0x401431, 0x7fffe3875838, 0x7fffe3875838) = 0
__cxa_atexit(0x7f712aa98ba0, 0, 0, 0) = 0
malloc(4) = 0x76ea30
dlopen("/usr/lib/x86_64-linux-gnu/libm.s"..., 1) = 0x76ea80
dlsym(0x76ea80, "cos") = 0x7f712a8abd00
dlerror() = nil
printf("%f\n", -0.416147-0.416147
) = 10
dlclose(0x76ea80) = 0
+++ exited (status 0) +++
As you can see, the call to cos was skipped.
How can I trace that with that arguments ?
I gave a try to uftrace
But again, It doesn't trace the cos call:
uftrace -a --libname --nest-libcall ./a.out
-0.416147
# DURATION TID FUNCTION
[ 8300] | main() {
1.754 us [ 8300] | malloc@libc-2.31.so(4) = 0x15c6120;
509.774 us [ 8300] | dlopen@libdl-2.31.so("/usr/lib/x86_64-linux-gnu/libm.so.6", RTLD_LAZY) = 0x7ff70ae4d090;
2.140 us [ 8300] | dlsym@libdl-2.31.so(0x7ff70ae4d090, "cos") = 0x7ff70aa61d00;
0.463 us [ 8300] | dlerror@libdl-2.31.so() = "NULL";
332.451 us [ 8300] | printf@libc-2.31.so("%f\n") = 10;
2.134 us [ 8300] | dlclose@libdl-2.31.so(0x7ff70ae4d090) = 0;
958.926 us [ 8300] | } /*
Which is surprising because on this comment it looks like it works.
Running on Ubuntu 20.04
- ltrace:
0.7.3 - uftrace:
0.9.3
Thank you for your help !
