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Re: [PATCH] Improve bndmov encoding with zero displacement
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 9 Jul 2015 09:31:34 -0700
- Subject: Re: [PATCH] Improve bndmov encoding with zero displacement
- Authentication-results: sourceware.org; auth=none
- References: <20150708195709 dot GA8828 at intel dot com>
On Wed, Jul 8, 2015 at 12:57 PM, H.J. Lu <hongjiu.lu@intel.com> wrote:
> If x86-64 assembler doesn't support MPX, we encode bndmov instruction by
> hand. When displacement is zero, assembler generates shorter encoding.
> This patch improves bndmov encoding with zero displacement so that ld.so
> is identical when using assemblers with and without MPX support.
>
> Verified using assemblers with and without MPX support. OK for trunk?
>
> H.J.
> --
> * sysdeps/x86_64/dl-trampoline.S (_dl_runtime_resolve): Improve
> bndmov encoding with zero displacement.
> ---
> sysdeps/x86_64/dl-trampoline.S | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/sysdeps/x86_64/dl-trampoline.S b/sysdeps/x86_64/dl-trampoline.S
> index b151d35..678c57f 100644
> --- a/sysdeps/x86_64/dl-trampoline.S
> +++ b/sysdeps/x86_64/dl-trampoline.S
> @@ -80,7 +80,11 @@ _dl_runtime_resolve:
> bndmov %bnd2, REGISTER_SAVE_BND2(%rsp)
> bndmov %bnd3, REGISTER_SAVE_BND3(%rsp)
> # else
> +# if REGISTER_SAVE_BND0 == 0
> + .byte 0x66,0x0f,0x1b,0x04,0x24
> +# else
> .byte 0x66,0x0f,0x1b,0x44,0x24,REGISTER_SAVE_BND0
> +# endif
> .byte 0x66,0x0f,0x1b,0x4c,0x24,REGISTER_SAVE_BND1
> .byte 0x66,0x0f,0x1b,0x54,0x24,REGISTER_SAVE_BND2
> .byte 0x66,0x0f,0x1b,0x5c,0x24,REGISTER_SAVE_BND3
> @@ -104,7 +108,11 @@ _dl_runtime_resolve:
> .byte 0x66,0x0f,0x1a,0x5c,0x24,REGISTER_SAVE_BND3
> .byte 0x66,0x0f,0x1a,0x54,0x24,REGISTER_SAVE_BND2
> .byte 0x66,0x0f,0x1a,0x4c,0x24,REGISTER_SAVE_BND1
> +# if REGISTER_SAVE_BND0 == 0
> + .byte 0x66,0x0f,0x1a,0x04,0x24
> +# else
> .byte 0x66,0x0f,0x1a,0x44,0x24,REGISTER_SAVE_BND0
> +# endif
> # endif
> #endif
> # Get register content back.
> --
> 2.4.3
>
I checked it in.
--
H.J.