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Re: CVS commit: src/lib/librumphijack
On Fri, Feb 25, 2011 at 16:01:42 +0000, Antti Kantee wrote:
> Module Name: src
> Committed By: pooka
> Date: Fri Feb 25 16:01:42 UTC 2011
>
> Modified Files:
> src/lib/librumphijack: Makefile hijackdlsym.c
>
> Log Message:
> Ok, for reasons I can't begin to understand, the binaries I tested
> yesterday on powerpc broke overnight. Apparently adding one more
> function before the call to dlsym() fixes things again. I hope
> I don't have to add another one tomorrow ....
>
>
> To generate a diff of this commit:
> cvs rdiff -u -r1.7 -r1.8 src/lib/librumphijack/Makefile
> cvs rdiff -u -r1.1 -r1.2 src/lib/librumphijack/hijackdlsym.c
I think this is caused by revision 1.121 of rtld.c (hi, mac!) that
added "hackish_return_address" for ppc.
#ifdef __powerpc__
static void *
hackish_return_address(void)
{
return __builtin_return_address(1);
}
#endif
void *
dlsym(void *handle, const char *name)
{
...
#ifdef __powerpc__
retaddr = hackish_return_address();
#else
retaddr = __builtin_return_address(0);
#endif
...
}
hackish_return_address will be inlined (simple static function) and,
as far as I can tell, gcc does NOT adjust the "level" argument to
__builtin_return_address.
The net effect is that dlsym uses caller's caller address to detect
which module the call comes from, and if caller's caller is in a
different module wrong things happen.
That explains why you need an extra frame.
-uwe
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