Re: Intercepting calls in PIC mode

You could hijack the GOT entry, but that assumes the symbol has been
resolved first (either LD_BIND_NOW or the function has been called at
least once). You could also use LD_PRELOAD.

On Jul 04, 2014 04:12 PM +0400, Ivan A. Kosarev wrote:
> Hello,
> 
> Consider the following:
> 
> ---
> #include <stdio.h>
> #include <string.h>
> 
> extern "C" void* memset(void *block, int c, size_t size)
>      __attribute__((weak, alias("__int_memset"), visibility("default")));
> 
> extern "C" __attribute__((visibility("default")))
> void* __int_memset(void *block, int c, size_t size) {
>      puts("Hello");
>      return NULL;
> }
> 
> int main()
> {
>      void *(*F)(void *b, int c, size_t len) = memset;
>      char a[5];
>      memset(a, 0, sizeof(a));
>      F(a, 0, sizeof(a));
>      return 0;
> }
> ---
> 
> It intercepts the memset() calls without issue on both x86-64 FreeBSD 
> 9.2 and Linux. However, with the -fPIC option specified in the cc's 
> command line, only the first (direct) call work on FreeBSD, but not the 
> second (indirect) one. Note is that on Linux both the calls are 
> intercepted--no matter whether the -fPIC option is specified or not.
> 
> The question is: is there a way to intercept indirect calls on FreeBSD?
> 
> Thanks,
> 
> -- 
> 
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