On Mon, Feb 23, 2009 at 10:39 AM, Jiri Olsa <olsaj...@gmail.com> wrote:
> On Mon, Feb 23, 2009 at 7:35 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>> On Mon, Feb 23, 2009 at 10:05 AM, Jiri Olsa <olsaj...@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...
>
Why isn't __outregs aligned at 16byte? According to x86-64 psABI,
La_x86_64_retval should be aligned at 16byte.
--
H.J.
