[Bug bootstrap/60830] [4.9 Regression] ICE on bootstrapping on cygwin

[ktietz at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60830

--- Comment #31 from Kai Tietz <ktietz at gcc dot gnu.org> ---
(In reply to Bernd Edlinger from comment #30)
> It looks like a bug in the assembler!
> 
> with objdump -d -r crtbegin.o we have wrong code:
> 
>   f3:   83 ec 04                sub    $0x4,%esp
>   f6:   85 c0                   test   %eax,%eax
>   f8:   ba f0 ff ff ff          mov    $0xfffffff0,%edx
>                         f9: dir32       ___deregister_frame_info
>   fd:   74 16                   je     115 <___gcc_deregister_frame+0x35>
> 
> 
> but the cygming-crtbegin.s looks correct:
> 
> LVL17:
>         .loc 1 158 0
>         testl   %eax, %eax
>         .loc 1 162 0
>         movl    $___deregister_frame_info, %edx
>         .loc 1 158 0
>         je      L27
> 
> 
> whenever there is a weak definition the reference is actually minus
> the offset of the previous weak definition. Everything is OK if that was
> at offset zero.
> 
> test case:
> 
> $ cat test.c
> #include <stdio.h>
> 
> extern void test() __attribute__((weak));
> 
> int main()
> {
>   printf("hello\n");
>   test();
>   return 0;
> }
> 
> __attribute__((weak))
> void test()
> {
>   printf("weak\n");
> }
> 
> $ cat test1.c
> #include <stdio.h>
> 
> void test()
> {
>   printf("strong\n");
> }
> 
> 
> $ gcc -o test test.c test1.c
> $ ./test
> hello
> Segmentation fault (core dumped)

Interesting finding.  So second issue cooks down to be an binutils bug about
weak.  I remember the cause of the change to gcc's crtbegin, and it is pretty
important one (at least for x64).  As the implicit zero-relocation doesn't work
on x64 as instructions have +/-2^31 offset in max.
So I would suggest to report this issue on binutils.  gcc's bz isn't the right
place to discuss that issue further.