Re: [PATCH] gdb: x86: fix x32 builds with inline asm

H.J. Lu
2013-01-08T17:50:21Z

On Tue, Jan 8, 2013 at 9:45 AM, Mike Frysinger <vapier@gentoo.org> wrote:
> On Tuesday 08 January 2013 11:54:32 H.J. Lu wrote:
>> On Tue, Jan 8, 2013 at 7:59 AM, Mike Frysinger <vapier@gentoo.org> wrote:
>> > On Tuesday 08 January 2013 10:01:20 Mike Frysinger wrote:
>> >> + asm volatile ("push %0;"
>> >> ".globl linux_ptrace_test_ret_to_nx_instr;"
>> >> "linux_ptrace_test_ret_to_nx_instr:"
>> >> "ret"
>> >> - : : "r" (return_address) : "%rsp", "memory");
>> >> + : : "r" (return_address) : "sp", "memory");
>> >
>> > hrm, this works for -m32 and -m64, but doesn't actually help with -mx32.
>> > this doesn't seem to line up with my expectations. can you suggest
>> > something here H.J. Lu ?
>> >
>> > $ cat test.c
>> > main() { asm volatile ("push %0; ret;" : : "r"(main) : "sp", "memory"); }
>> >
>> > $ gcc -m32 test.c
>> > 8: 50 push %eax
>> > 9: c3 ret
>> > $ gcc -m64 test.c
>> > 9: 50 push %rax
>> > a: c3 retq
>> >
>> > $ gcc -mx32 test.c
>> > test.c: Assembler messages:
>> > test.c:2: Error: operand type mismatch for `push'
>>
>> Can you try this?
>>
>> +#ifdef __x86_64__
>> + : : "r" ((uint64_t) (uintptr_t) (return_address))
>
> that seems to work for me, but seems wrong. i guess while most 32/64 bit
> issues can be handled transparently, the stack still only allows
> pushing/popping of 64bit values in x32 mode.
> -mike

I believe it is correct for x32 since "ret" will pop 64bit as return address
for x32.

--
H.J.