linux-kernel - Re: [PATCH 3/4] x86/asm/entry/64: use smaller insns

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Date:	Wed, 25 Mar 2015 11:03:11 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86/asm/entry/64: use smaller insns

On Wed, Mar 25, 2015 at 10:18 AM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> The $AUDIT_ARCH_X86_64 parameter to syscall_trace_enter_phase1/2
> is a 32-bit constant, loading it with 32-bit MOV produces 5-byte insn
> instead of 10-byte one.

Acked-by: Andy Lutomirski <luto@...nel.org>

>
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Ingo Molnar <mingo@...nel.org>
> CC: Borislav Petkov <bp@...en8.de>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Frederic Weisbecker <fweisbec@...il.com>
> CC: Alexei Starovoitov <ast@...mgrid.com>
> CC: Will Drewry <wad@...omium.org>
> CC: Kees Cook <keescook@...omium.org>
> CC: x86@...nel.org
> CC: linux-kernel@...r.kernel.org
> ---
>  arch/x86/kernel/entry_64.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 11b7339..23aa43e 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -306,7 +306,7 @@ system_call_fastpath:
>         /* Do syscall entry tracing */
>  tracesys:
>         movq %rsp, %rdi
> -       movq $AUDIT_ARCH_X86_64, %rsi
> +       movl $AUDIT_ARCH_X86_64, %esi
>         call syscall_trace_enter_phase1
>         test %rax, %rax
>         jnz tracesys_phase2             /* if needed, run the slow path */
> @@ -317,7 +317,7 @@ tracesys:
>  tracesys_phase2:
>         SAVE_EXTRA_REGS
>         movq %rsp, %rdi
> -       movq $AUDIT_ARCH_X86_64, %rsi
> +       movl $AUDIT_ARCH_X86_64, %esi
>         movq %rax,%rdx
>         call syscall_trace_enter_phase2
>
> --
> 1.8.1.4
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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