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Subject[tip:x86/asm] x86/asm/entry/64: Clean up usage of TEST insns
Commit-ID:  03335e95e27fc1f2b17b05b27342ad76986b3cf0
Gitweb: http://git.kernel.org/tip/03335e95e27fc1f2b17b05b27342ad76986b3cf0
Author: Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Mon, 27 Apr 2015 15:21:52 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 8 May 2015 11:07:32 +0200

x86/asm/entry/64: Clean up usage of TEST insns

By the nature of TEST operation, it is often possible
to test a narrower part of the operand:

"testl $3, mem" -> "testb $3, mem"

This results in shorter insns, because TEST insn has no
sign-entending byte-immediate forms unlike other ALU ops.

text data bss dec hex filename
11674 0 0 11674 2d9a entry_64.o.before
11658 0 0 11658 2d8a entry_64.o

Changes in object code:

- f7 84 24 88 00 00 00 03 00 00 00 testl $0x3,0x88(%rsp)
+ f6 84 24 88 00 00 00 03 testb $0x3,0x88(%rsp)
- f7 44 24 68 03 00 00 00 testl $0x3,0x68(%rsp)
+ f6 44 24 68 03 testb $0x3,0x68(%rsp)
- f7 84 24 90 00 00 00 03 00 00 00 testl $0x3,0x90(%rsp)
+ f6 84 24 90 00 00 00 03 testb $0x3,0x90(%rsp)

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1430140912-7960-2-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/entry_64.S | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 8f8b22a..60705b03 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -601,7 +601,7 @@ ENTRY(ret_from_fork)

RESTORE_EXTRA_REGS

- testl $3,CS(%rsp) # from kernel_thread?
+ testb $3, CS(%rsp) # from kernel_thread?

/*
* By the time we get here, we have no idea whether our pt_regs,
@@ -665,7 +665,7 @@ END(irq_entries_start)

leaq -RBP(%rsp),%rdi /* arg1 for \func (pointer to pt_regs) */

- testl $3, CS-RBP(%rsp)
+ testb $3, CS-RBP(%rsp)
jz 1f
SWAPGS
1:
@@ -720,7 +720,7 @@ ret_from_intr:
CFI_DEF_CFA_REGISTER rsp
CFI_ADJUST_CFA_OFFSET RBP

- testl $3,CS(%rsp)
+ testb $3, CS(%rsp)
jz retint_kernel
/* Interrupt came from user space */

@@ -968,7 +968,7 @@ ENTRY(\sym)
.if \paranoid
.if \paranoid == 1
CFI_REMEMBER_STATE
- testl $3, CS(%rsp) /* If coming from userspace, switch */
+ testb $3, CS(%rsp) /* If coming from userspace, switch */
jnz 1f /* stacks. */
.endif
call paranoid_entry
@@ -1309,7 +1309,7 @@ ENTRY(error_entry)
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
xorl %ebx,%ebx
- testl $3,CS+8(%rsp)
+ testb $3, CS+8(%rsp)
jz error_kernelspace
error_swapgs:
SWAPGS
@@ -1606,7 +1606,6 @@ end_repeat_nmi:
je 1f
movq %r12, %cr2
1:
-
testl %ebx,%ebx /* swapgs needed? */
jnz nmi_restore
nmi_swapgs:

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