linux-kernel - Re: [PATCH 5/6] x86: ia32entry.S: fold IA32_ARG

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Date:	Mon, 23 Feb 2015 16:35:33 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] x86: ia32entry.S: fold IA32_ARG_FIXUP macro into its callers

On Mon, Feb 23, 2015 at 4:12 PM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> Use of a small macro - one with conditional expansion - does more harm
> than good. It obfuscates code, with minimal code reuse.
>
> For example, because of obfuscation it's not obvious that
> in ia32_sysenter_target, we can optimize loading of r9 -
> currently it is loaded with a detour through ebp.
>
> This patch folds IA32_ARG_FIXUP macro into its callers.
>
> No code changes.
>

Applied.

> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Borislav Petkov <bp@...en8.de>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Frederic Weisbecker <fweisbec@...il.com>
> CC: X86 ML <x86@...nel.org>
> CC: Alexei Starovoitov <ast@...mgrid.com>
> CC: Will Drewry <wad@...omium.org>
> CC: Kees Cook <keescook@...omium.org>
> CC: linux-kernel@...r.kernel.org
> ---
>  arch/x86/ia32/ia32entry.S | 32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> index b567056..6dcd372 100644
> --- a/arch/x86/ia32/ia32entry.S
> +++ b/arch/x86/ia32/ia32entry.S
> @@ -30,17 +30,6 @@
>
>         .section .entry.text, "ax"
>
> -       .macro IA32_ARG_FIXUP noebp=0
> -       movl    %edi,%r8d
> -       .if \noebp
> -       .else
> -       movl    %ebp,%r9d
> -       .endif
> -       xchg    %ecx,%esi
> -       movl    %ebx,%edi
> -       movl    %edx,%edx       /* zero extension */
> -       .endm
> -
>         /* clobbers %rax */
>         .macro  CLEAR_RREGS _r9=rax
>         xorl    %eax,%eax
> @@ -178,7 +167,12 @@ sysenter_flags_fixed:
>         cmpq    $(IA32_NR_syscalls-1),%rax
>         ja      ia32_badsys
>  sysenter_do_call:
> -       IA32_ARG_FIXUP
> +       /* 32bit syscall -> 64bit C ABI argument conversion */
> +       movl    %edi,%r8d       /* arg5 */
> +       movl    %ebp,%r9d       /* arg6 */
> +       xchg    %ecx,%esi       /* rsi:arg2, rcx:arg4 */
> +       movl    %ebx,%edi       /* arg1 */
> +       movl    %edx,%edx       /* arg3 (zero extension) */
>  sysenter_dispatch:
>         call    *ia32_sys_call_table(,%rax,8)
>         movq    %rax,RAX(%rsp)
> @@ -360,7 +354,12 @@ ENTRY(ia32_cstar_target)
>         cmpq $IA32_NR_syscalls-1,%rax
>         ja  ia32_badsys
>  cstar_do_call:
> -       IA32_ARG_FIXUP 1
> +       /* 32bit syscall -> 64bit C ABI argument conversion */
> +       movl    %edi,%r8d       /* arg5 */
> +       /* r9 already loaded */ /* arg6 */
> +       xchg    %ecx,%esi       /* rsi:arg2, rcx:arg4 */
> +       movl    %ebx,%edi       /* arg1 */
> +       movl    %edx,%edx       /* arg3 (zero extension) */
>  cstar_dispatch:
>         call *ia32_sys_call_table(,%rax,8)
>         movq %rax,RAX(%rsp)
> @@ -477,7 +476,12 @@ ENTRY(ia32_syscall)
>         cmpq $(IA32_NR_syscalls-1),%rax
>         ja ia32_badsys
>  ia32_do_call:
> -       IA32_ARG_FIXUP
> +       /* 32bit syscall -> 64bit C ABI argument conversion */
> +       movl %edi,%r8d  /* arg5 */
> +       movl %ebp,%r9d  /* arg6 */
> +       xchg %ecx,%esi  /* rsi:arg2, rcx:arg4 */
> +       movl %ebx,%edi  /* arg1 */
> +       movl %edx,%edx  /* arg3 (zero extension) */
>         call *ia32_sys_call_table(,%rax,8) # xxx: rip relative
>  ia32_sysret:
>         movq %rax,RAX(%rsp)
> --
> 1.8.1.4
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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