linux-kernel - [PATCH] x86-64: cleanup some assembly entry points

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Date:	Tue, 29 Nov 2011 11:24:10 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	<mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] x86-64: cleanup some assembly entry points

system_call_after_swapgs doesn't really benefit from forcing alignment
from it - quite the opposite, native code needlessly so far got a big
NOP instruction inserted in front of it. Xen being the only user of
the separate entry point can well live with the branch going to three
bytes into a cache line.

The compatibility mode ptregs entry points for one can make use of the
GLOBAL() macro, and should be suitably aligned. Their shared
continuation point (ia32_ptregs_common) otoh doesn't need to be global
at all, but should continue to be properly aligned.

Signed-off-by: Jan Beulich <jbeulich@...e.com>

---
 arch/x86/ia32/ia32entry.S  |    7 ++++---
 arch/x86/kernel/entry_64.S |    2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

--- 3.2-rc3/arch/x86/ia32/ia32entry.S
+++ 3.2-rc3-x86_64-entry-cleanup/arch/x86/ia32/ia32entry.S
@@ -459,8 +459,8 @@ quiet_ni_syscall:
 	CFI_ENDPROC
 	
 	.macro PTREGSCALL label, func, arg
-	.globl \label
-\label:
+	ALIGN
+GLOBAL(\label)
 	leaq \func(%rip),%rax
 	leaq -ARGOFFSET+8(%rsp),\arg	/* 8 for return address */
 	jmp  ia32_ptregs_common	
@@ -477,7 +477,8 @@ quiet_ni_syscall:
 	PTREGSCALL stub32_vfork, sys_vfork, %rdi
 	PTREGSCALL stub32_iopl, sys_iopl, %rsi
 
-ENTRY(ia32_ptregs_common)
+	ALIGN
+ia32_ptregs_common:
 	popq %r11
 	CFI_ENDPROC
 	CFI_STARTPROC32	simple
--- 3.2-rc3/arch/x86/kernel/entry_64.S
+++ 3.2-rc3-x86_64-entry-cleanup/arch/x86/kernel/entry_64.S
@@ -465,7 +465,7 @@ ENTRY(system_call)
 	 * after the swapgs, so that it can do the swapgs
 	 * for the guest and jump here on syscall.
 	 */
-ENTRY(system_call_after_swapgs)
+GLOBAL(system_call_after_swapgs)
 
 	movq	%rsp,PER_CPU_VAR(old_rsp)
 	movq	PER_CPU_VAR(kernel_stack),%rsp



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