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.
