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Re: generated movaps with unaligned memory


On Mon, Feb 23, 2009 at 7:35 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Feb 23, 2009 at 10:05 AM, Jiri Olsa <olsajiri@gmail.com> wrote:
>> Hi,
>>
>> my shared library crashes with movaps instruction using not aligned memory.
>>
>> Since the shared library function is being called from dynamic linker, which
>> basically prepares the memory location, I'm not sure whoose side issues this is.
>>
>> I have following function in C:
>>
>> typedef float La_x86_64_xmm __attribute__ ((__vector_size__ (16)));
>>
>> typedef struct La_x86_64_retval
>> {
>>  uint64_t lrv_rax;
>>  uint64_t lrv_rdx;
>>  La_x86_64_xmm lrv_xmm0;
>>  La_x86_64_xmm lrv_xmm1;
>>  long double lrv_st0;
>>  long double lrv_st1;
>> } La_x86_64_retval;
>>
>> unsigned int la_x86_64_gnu_pltexit (Elf64_Sym *__sym,
>>               unsigned int __ndx, uintptr_t *__refcook, uintptr_t *__defcook,
>>               const La_x86_64_regs *__inregs, La_x86_64_retval
>> *__outregs, const char *symname)
>> {
>>       La_x86_64_xmm b __attribute__ ((aligned(16)));
>>       b = __outregs->lrv_xmm0;
>>       return 0;
>> }
>>
>> this will endup in following assembly:
>>
>> 00000000000007d7 <la_x86_64_gnu_pltexit>:
>>  7d7:   55                      push   %rbp
>>  7d8:   48 89 e5                mov    %rsp,%rbp
>>  7db:   48 89 7d e8             mov    %rdi,-0x18(%rbp)
>>  7df:   89 75 e4                mov    %esi,-0x1c(%rbp)
>>  7e2:   48 89 55 d8             mov    %rdx,-0x28(%rbp)
>>  7e6:   48 89 4d d0             mov    %rcx,-0x30(%rbp)
>>  7ea:   4c 89 45 c8             mov    %r8,-0x38(%rbp)
>>  7ee:   4c 89 4d c0             mov    %r9,-0x40(%rbp)
>>  7f2:   48 8b 45 c0             mov    -0x40(%rbp),%rax
>>  7f6:   0f 28 40 10             movaps 0x10(%rax),%xmm0
>>  7fa:   0f 29 45 f0             movaps %xmm0,-0x10(%rbp)
>>  7fe:   b8 00 00 00 00          mov    $0x0,%eax
>>  803:   c9                      leaveq
>>  804:   c3                      retq
>>
>>
>> Looks like xmm0 register is being used to transfer the data. However
>> the structure's alignment is not 16, so it will crash.
>>
>
> Where exactly is it crashed? Which the structure isn't aligned at 16byte?
>
>
>
> --
> H.J.
>


sry, it crashes on this one

 7f6:   0f 28 40 10             movaps 0x10(%rax),%xmm0

This structure/argument is not aligned at 16
La_x86_64_retval *__outreg

the '__outregs->lrv_xmm0' is at 16th byte of the structure...

jirka


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