Re: [PATCH] x86-64: Fix the dtv field load for x32 [BZ #31184]

Re: [PATCH] x86-64: Fix the dtv field load for x32 [BZ #31184]

[H.J. Lu]

On Wed, Dec 20, 2023 at 4:31 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On x32, I got
>
> FAIL: elf/tst-tlsgap
>
> $ gdb elf/tst-tlsgap
> ...
> open tst-tlsgap-mod1.so
>
> Thread 2 "tst-tlsgap" received signal SIGSEGV, Segmentation fault.
> [Switching to LWP 2268754]
> _dl_tlsdesc_dynamic () at ../sysdeps/x86_64/dl-tlsdesc.S:108
> 108             movq    (%rsi), %rax
> (gdb) p/x $rsi
> $4 = 0xf7dbf9005655fb18
> (gdb)
>
> This is caused by
>
> _dl_tlsdesc_dynamic:
>         _CET_ENDBR
>         /* Preserve call-clobbered registers that we modify.
>            We need two scratch regs anyway.  */
>         movq    %rsi, -16(%rsp)
>         movq    %fs:DTV_OFFSET, %rsi
>
> Since the dtv field in TCB is a pointer, %fs:DTV_OFFSET is a 32-bit
> location, not 64-bit.  Load the dtv field to RSI_LP instead of rsi.
> This fixes BZ #31184.
> ---
>  sysdeps/x86_64/dl-tlsdesc.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sysdeps/x86_64/dl-tlsdesc.S b/sysdeps/x86_64/dl-tlsdesc.S
> index 5593897e29..c4823547d7 100644
> --- a/sysdeps/x86_64/dl-tlsdesc.S
> +++ b/sysdeps/x86_64/dl-tlsdesc.S
> @@ -102,7 +102,7 @@ _dl_tlsdesc_dynamic:
>         /* Preserve call-clobbered registers that we modify.
>            We need two scratch regs anyway.  */
>         movq    %rsi, -16(%rsp)
> -       movq    %fs:DTV_OFFSET, %rsi
> +       mov     %fs:DTV_OFFSET, %RSI_LP
>         movq    %rdi, -8(%rsp)
>         movq    TLSDESC_ARG(%rax), %rdi
>         movq    (%rsi), %rax
> --
> 2.43.0
>

I will check it in tomorrow and back it to release branches later.

Thanks.

-- 
H.J.