[tip: objtool/core] x86,ftrace: Shrink ftrace_regs_caller() by one byte

From: tip-bot2 for Peter Zijlstra
Date: Thu Apr 23 2020 - 03:50:49 EST


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@xxxxxxxxxxxxx>
AuthorDate: Wed, 01 Apr 2020 16:51:11 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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@xxxxxxxxxxxxx>
Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Reviewed-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200416115118.867411350@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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