linux-kernel - [PATCH 8/9] x86/asm/entry/64: simplify jumps in ret_from

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Date:	Thu,  2 Apr 2015 16:36:17 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 8/9] x86/asm/entry/64: simplify jumps in ret_from_fork

Replace
        test
        jz  1f
        jmp label
    1:

with
        test
        jnz label

Run-tested.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Borislav Petkov <bp@...en8.de>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Alexei Starovoitov <ast@...mgrid.com>
CC: Will Drewry <wad@...omium.org>
CC: Kees Cook <keescook@...omium.org>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/entry_64.S | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 36a360a..0124f6f 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -512,18 +512,18 @@ ENTRY(ret_from_fork)
 	RESTORE_EXTRA_REGS
 
 	testl $3,CS(%rsp)			# from kernel_thread?
-	jz   1f
 
 	/*
 	 * By the time we get here, we have no idea whether our pt_regs,
 	 * ti flags, and ti status came from the 64-bit SYSCALL fast path,
 	 * the slow path, or one of the ia32entry paths.
-	 * Use int_ret_from_sys_call to return, since it can safely handle
+	 * Use IRET code path to return, since it can safely handle
 	 * all of the above.
 	 */
-	jmp  int_ret_from_sys_call
+	jnz	int_ret_from_sys_call
 
-1:
+	/* We came from from kernel_thread */
+	/* nb: we depend on RESTORE_EXTRA_REGS above */
 	movq %rbp, %rdi
 	call *%rbx
 	xorl	%eax, %eax
-- 
1.8.1.4

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