linux-kernel - [PATCH 16/17] x86: entry_64.S: trivial optimization for ENOSYS

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Date:	Fri,  8 Aug 2014 19:44:39 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	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>
Subject: [PATCH 16/17] x86: entry_64.S: trivial optimization for ENOSYS

This code uses a slightly shorter insn.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Oleg Nesterov <oleg@...hat.com>
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/kernel/entry_64.S | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 7bc8c24..5d639a6 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -272,6 +272,7 @@ system_call_fastpath:
 	ja badsys
 	movq %r10,%rcx
 	call *sys_call_table(,%rax,8)  # XXX:	 rip relative
+from_badsys:
 	movq %rax,RAX(%rsp)
 /*
  * Syscall return path ending with SYSRET (fast path)
@@ -334,8 +335,8 @@ sysret_signal:
 	jmp int_check_syscall_exit_work
 
 badsys:
-	movq $-ENOSYS,RAX(%rsp)
-	jmp ret_from_sys_call
+	movq	$-ENOSYS,%rax
+	jmp	from_badsys
 
 #ifdef CONFIG_AUDITSYSCALL
 	/*
-- 
1.8.1.4

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