linux-kernel - [tip:x86/asm] x86/asm/entry/64/compat: Fold the IA32_ARG

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Message-ID: <tip-14f6e9532dda399a7b789f744dc045f8865a9e42@git.kernel.org>
Date:	Wed, 4 Mar 2015 14:55:49 -0800
From:	tip-bot for Denys Vlasenko <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, luto@...capital.net, ast@...mgrid.com,
	tglx@...utronix.de, torvalds@...ux-foundation.org,
	fweisbec@...il.com, bp@...en8.de, wad@...omium.org,
	dvlasenk@...hat.com, mingo@...nel.org,
	linux-kernel@...r.kernel.org, keescook@...omium.org,
	oleg@...hat.com
Subject: [tip:x86/asm] x86/asm/entry/64/compat:
  Fold the IA32_ARG_FIXUP macro into its callers

Commit-ID:  14f6e9532dda399a7b789f744dc045f8865a9e42
Gitweb:     http://git.kernel.org/tip/14f6e9532dda399a7b789f744dc045f8865a9e42
Author:     Denys Vlasenko <dvlasenk@...hat.com>
AuthorDate: Thu, 26 Feb 2015 14:40:35 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 4 Mar 2015 22:50:52 +0100

x86/asm/entry/64/compat: Fold the IA32_ARG_FIXUP macro into its callers

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 the IA32_ARG_FIXUP macro into its callers.

No code changes.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
Signed-off-by: Andy Lutomirski <luto@...capital.net>
Cc: Alexei Starovoitov <ast@...mgrid.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Will Drewry <wad@...omium.org>
Link: http://lkml.kernel.org/r/4da092094cd78734384ac31e0d4ec1d8f69145a2.1424989793.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@...nel.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)
--
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