linux-kernel - [PATCH 2/3] arm/syscalls: Optimize work flags assembly check

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Message-Id: <20170719175900.124074-2-thgarnie@google.com>
Date:   Wed, 19 Jul 2017 10:58:59 -0700
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Russell King <linux@...linux.org.uk>,
        Thomas Garnier <thgarnie@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Dave Martin <Dave.Martin@....com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Pratyush Anand <panand@...hat.com>, leonard.crestez@....com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: [PATCH 2/3] arm/syscalls: Optimize work flags assembly check

Remove the double branch and use tsteq instead.

Suggested-by: Russell King <linux@...linux.org.uk>
Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
 arch/arm/kernel/entry-common.S | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index e33c32d56193..6e094b639d83 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -42,8 +42,7 @@ ret_fast_syscall:
 	disable_irq_notrace			@ disable interrupts
 	ldr	r1, [tsk, #TI_FLAGS]		@ re-check for syscall tracing
 	tst	r1, #_TIF_SYSCALL_WORK
-	bne	fast_work_pending
-	tst	r1, #_TIF_WORK_MASK
+	tsteq   r1, #_TIF_WORK_MASK
 	bne	fast_work_pending
 
 	/* perform architecture specific actions before user return */
@@ -70,14 +69,12 @@ ret_fast_syscall:
 	disable_irq_notrace			@ disable interrupts
 	ldr	r1, [tsk, #TI_FLAGS]		@ re-check for syscall tracing
 	tst	r1, #_TIF_SYSCALL_WORK
-	bne	fast_work_pending
-	tst	r1, #_TIF_WORK_MASK
+	tsteq   r1, #_TIF_WORK_MASK
 	beq	no_work_pending
  UNWIND(.fnend		)
 ENDPROC(ret_fast_syscall)
 
 	/* Slower path - fall through to work_pending */
-fast_work_pending:
 #endif
 
 	tst	r1, #_TIF_SYSCALL_WORK
-- 
2.14.0.rc0.284.gd933b75aa4-goog