Control: retitle -1: segmentation fault on any code due to new binutils
relocations
On 2015-12-15 12:34, Vincent Lefevre wrote:
> Control: retitle -1 segmentation fault on any code compiled by tcc with libc6
> 2.21-4
>
> Cc to the glibc maintainers because the cause of the bug is due to
> some change in glibc.
I don't think it's related to the glibc. It's related to the fact that
glibc 2.21-4 in unstable is built with a recent binutils, introducing
some changes in the relocations. If you rebuild glibc 2.21-4 with
binutils 2.25.1-7, the problem disappears.
> On 2015-12-15 09:35:04 +0100, Vincent Lefevre wrote:
> > Code compiled by tcc segfaults:
> >
> > ypig% cat conftest.c
> > int main (void)
> > { return 0; }
> > ypig% tcc conftest.c -o conftest
> > ypig% ./conftest
> > zsh: segmentation fault (core dumped) ./conftest
>
> The cause is libc6 2.21. I get this problem with libc6 2.21-4,
> but on another machine, after reverting to libc6 2.19-22, this
> problem no longer occurs. So, I wonder whether this is a tcc
> bug or a glibc one.
>
> In the "objdump -S" output of conftest, I notice the following
> difference:
>
> libc6 2.19:
>
> 0000000000400430 <_init>:
> 400430: 48 83 ec 08 sub $0x8,%rsp
> 400434: 48 8b 05 4d 01 20 00 mov 0x20014d(%rip),%rax #
> 600588 <_init+0x200158>
> [...]
>
> libc6 2.21:
>
> 00000000004003f0 <_init>:
> 4003f0: 48 83 ec 08 sub $0x8,%rsp
> 4003f4: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # 4003fb
> <_init+0xb>
>
> The 0x20014d(%rip) has changed to 0x0(%rip).
This is due to the following change in crti.o:
2.19:
| 000000000000000 <_init>:
| 0: 48 83 ec 08 sub $0x8,%rsp
| 4: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # b <_init+0xb>
| 7: R_X86_64_GOTPCREL __gmon_start__-0x4
| b: 48 85 c0 test %rax,%rax
| e: 74 05 je 15 <_init+0x15>
| 10: e8 00 00 00 00 callq 15 <_init+0x15>
| 11: R_X86_64_PLT32 __gmon_start__-0x4
|
12.21:
| 0000000000000000 <_init>:
| 0: 48 83 ec 08 sub $0x8,%rsp
| 4: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # b <_init+0xb>
| 7: R_X86_64_REX_GOTPCRELX __gmon_start__-0x4
| b: 48 85 c0 test %rax,%rax
| e: 74 05 je 15 <_init+0x15>
| 10: e8 00 00 00 00 callq 15 <_init+0x15>
| 11: R_X86_64_PLT32 __gmon_start__-0x4
As you can see the R_X86_64_GOTPCREL has been replaced by a new
relocation type R_X86_64_REX_GOTPCRELX. It looks like TCC doesn't
support it.
Aurelien
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
aurel...@aurel32.net http://www.aurel32.net
