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

Mike Frysinger
2013-01-08T17:42:58Z

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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

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