On Fri, May 13, 2016 at 9:07 AM, Uros Bizjak <ubiz...@gmail.com> wrote:
> On Fri, May 13, 2016 at 1:20 AM, H.J. Lu <hjl.to...@gmail.com> wrote:
>
>>>> testsuite/gcc.target/i386/pr61599-{1,2}.c testcases expose a failure
>>>> with -mcmodel -fpic, where:
>>>>
>>>> /tmp/ccfpoxHY.o: In function `bar':
>>>> pr61599-2.c:(.text+0xe): relocation truncated to fit: R_X86_64_PC32
>>>> against symbol `a' defined in LARGE_COMMON section in /tmp/ccKTKST2.o
>>>> collect2: error: ld returned 1 exit status
>>>> compiler exited with status 1
>>>>
>>>> CM_MEDIUM_PIC code model assumes that code+got/plt fits in a 31 bit
>>>> region, data is unlimited. Based on these assumptions, code should be
>>>> accessed via R_X86_64_GOT64.
>>>>
>>>> Attached patch uses UNSPEC_GOT instead of UNSPEC_GOTPCREL also for
>>>> CM_MEDIUM_PIC.
>>>>
>>>> 2016-05-12 Uros Bizjak <ubiz...@gmail.com>
>>>>
>>>> PR target/61599
>>>> * config/i386/i386.c (legitimize_pic_address): Do not use
>>>> UNSPEC_GOTPCREL for CM_MEDIUM_PIC code model.
>>>>
>>>> Patch was bootstrapped on x86_64-linux-gnu and regression tested with
>>>> -mcmodel=medium -fpic.
>>>>
>>>> Jakub, H.J., do you have any comments on the patch?
>>>
>>>
>>> I prefer this patch.
> Yes, your patch is more precise.
OTOH, are we sure there is no linker bug here? We have:
$ objdump -dr pr61599-1a.o
pr61599-1a.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <main>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 8d 05 00 00 00 00 lea 0x0(%rip),%rax # b <main+0xb>
7: R_X86_64_GOTPC32 _GLOBAL_OFFSET_TABLE_-0x4
b: b8 00 00 00 00 mov $0x0,%eax
10: e8 00 00 00 00 callq 15 <main+0x15>
11: R_X86_64_PLT32 bar-0x4
15: 89 c2 mov %eax,%edx
17: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # 1e <main+0x1e>
1a: R_X86_64_GOTPCREL c-0x4
1e: 0f b6 80 e1 00 00 00 movzbl 0xe1(%rax),%eax
25: 0f be c0 movsbl %al,%eax
28: 01 d0 add %edx,%eax
2a: 5d pop %rbp
2b: c3 retq
$ objdump -dr pr61599-2a.o
pr61599-2a.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <bar>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 8d 05 00 00 00 00 lea 0x0(%rip),%rax # b <bar+0xb>
7: R_X86_64_GOTPC32 _GLOBAL_OFFSET_TABLE_-0x4
b: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # 12 <bar+0x12>
e: R_X86_64_GOTPCREL a-0x4
12: 0f b6 40 02 movzbl 0x2(%rax),%eax
16: 0f be d0 movsbl %al,%edx
19: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # 20 <bar+0x20>
1c: R_X86_64_GOTPCREL b-0x4
20: 0f b6 40 10 movzbl 0x10(%rax),%eax
24: 0f be c0 movsbl %al,%eax
27: 01 c2 add %eax,%edx
29: 48 8b 05 00 00 00 00 mov 0x0(%rip),%rax # 30 <bar+0x30>
2c: R_X86_64_GOTPCREL c-0x4
30: 0f b6 80 00 01 00 00 movzbl 0x100(%rax),%eax
37: 0f be c0 movsbl %al,%eax
3a: 01 d0 add %edx,%eax
3c: 5d pop %rbp
3d: c3 retq
$ gcc pr61599-2a.o pr61599-1a.o
pr61599-2a.o: In function `bar':
pr61599-2a.c:(.text+0xe): relocation truncated to fit: R_X86_64_PC32
against symbol `a' defined in LARGE_COMMON section in pr61599-1a.o
collect2: error: ld returned 1 exit status
There is no R_X86_64_PC32 in pr61599-2a.o, only X86_64_GOTPCREL, which
according to assumptions, would reach all entries in the GOT table.
Uros.
