https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66826
Yuri Gribov <tetra2005 at gmail dot com> changed:
What |Removed |Added
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CC| |tetra2005 at gmail dot com
--- Comment #3 from Yuri Gribov <tetra2005 at gmail dot com> ---
This is a very funny bug but not related to GCC per se. Firstly, let's consider
a miminal repro:
__attribute__((constructor)) static void some_init() {
dlsym(RTLD_DEFAULT, "anything");
}
(segfaults just as well). Under -O0 this produces a normal call:
call dlsym@PLT
...
ret
but with -O2 GCC is clever enough to tail-call-optimize it to a plain jump:
jmp dlsym@PLT
Now dlsym (and other dl-functions) secretly take shadow parameter - return
address on stack:
void *
__dlsym (void *handle, const char *name DL_CALLER_DECL)
{
...
struct dlsym_args args;
args.who = DL_CALLER;
args.handle = handle;
args.name = name;
(from dlsym.c). As in our case return address is missing, args.who argument is
missing which causes segfault during symbol resolution (dynamic linker is lame
on checks).
