linux-kernel - [tip: objtool/core] x86,ftrace: Shrink ftrace_regs

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Date:   Thu, 23 Apr 2020 07:49:39 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: objtool/core] x86,ftrace: Shrink ftrace_regs_caller() by one byte

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     9f2dfd61dd022d4559d42a832fb03e76aad36c5f
Gitweb:        https://git.kernel.org/tip/9f2dfd61dd022d4559d42a832fb03e76aad36c5f
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Wed, 01 Apr 2020 16:51:11 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 22 Apr 2020 10:53:50 +02:00

x86,ftrace: Shrink ftrace_regs_caller() by one byte

'Optimize' ftrace_regs_caller. Instead of comparing against an
immediate, the more natural way to test for zero on x86 is: 'test
%r,%r'.

  48 83 f8 00             cmp    $0x0,%rax
  74 49                   je     226 <ftrace_regs_call+0xa3>

  48 85 c0                test   %rax,%rax
  74 49                   je     225 <ftrace_regs_call+0xa2>

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Miroslav Benes <mbenes@...e.cz>
Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>
Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lkml.kernel.org/r/20200416115118.867411350@infradead.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/ftrace_64.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index be9aff2..9738ed2 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -240,8 +240,8 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
 	 * See arch_ftrace_set_direct_caller().
 	 */
 	movq ORIG_RAX(%rsp), %rax
-	cmpq	$0, %rax
-	je	1f
+	testq	%rax, %rax
+	jz	1f
 
 	/* Swap the flags with orig_rax */
 	movq MCOUNT_REG_SIZE(%rsp), %rdi