linux-kernel - [PATCH 2/7] powerpc/lib: inline memcmp() NUL size verification

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Date:   Tue, 17 Apr 2018 09:38:37 +0200 (CEST)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH  2/7] powerpc/lib: inline memcmp() NUL size verification

Many calls to memcmp() are done with constant size.
This patch gives GCC a chance to optimise out
the NULL size verification.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/include/asm/string.h | 10 ++++++++++
 arch/powerpc/lib/memcmp_64.S      |  4 ++++
 arch/powerpc/lib/string_32.S      |  4 ++++
 3 files changed, 18 insertions(+)

diff --git a/arch/powerpc/include/asm/string.h b/arch/powerpc/include/asm/string.h
index 9b8cedf618f4..cf6f495134c3 100644
--- a/arch/powerpc/include/asm/string.h
+++ b/arch/powerpc/include/asm/string.h
@@ -27,6 +27,16 @@ extern int memcmp(const void *,const void *,__kernel_size_t);
 extern void * memchr(const void *,int,__kernel_size_t);
 extern void * memcpy_flushcache(void *,const void *,__kernel_size_t);
 
+#ifndef CONFIG_FORTIFY_SOURCE
+static inline int __memcmp(const void *p,const void *q,__kernel_size_t size)
+{
+	if (unlikely(!size))
+		return 0;
+	return memcmp(p, q, size);
+}
+#define memcmp __memcmp
+#endif
+
 #ifdef CONFIG_PPC64
 #define __HAVE_ARCH_MEMSET32
 #define __HAVE_ARCH_MEMSET64
diff --git a/arch/powerpc/lib/memcmp_64.S b/arch/powerpc/lib/memcmp_64.S
index d75d18b7bd55..f6822fabf254 100644
--- a/arch/powerpc/lib/memcmp_64.S
+++ b/arch/powerpc/lib/memcmp_64.S
@@ -30,7 +30,9 @@
 #endif
 
 _GLOBAL(memcmp)
+#ifdef CONFIG_FORTIFY_SOURCE
 	cmpdi	cr1,r5,0
+#endif
 
 	/* Use the short loop if both strings are not 8B aligned */
 	or	r6,r3,r4
@@ -39,7 +41,9 @@ _GLOBAL(memcmp)
 	/* Use the short loop if length is less than 32B */
 	cmpdi	cr6,r5,31
 
+#ifdef CONFIG_FORTIFY_SOURCE
 	beq	cr1,.Lzero
+#endif
 	bne	.Lshort
 	bgt	cr6,.Llong
 
diff --git a/arch/powerpc/lib/string_32.S b/arch/powerpc/lib/string_32.S
index 2519f8bd09e3..94e9c9bc31c3 100644
--- a/arch/powerpc/lib/string_32.S
+++ b/arch/powerpc/lib/string_32.S
@@ -15,8 +15,10 @@
 	.text
 
 _GLOBAL(memcmp)
+#ifdef CONFIG_FORTIFY_SOURCE
 	PPC_LCMPI 0,r5,0
 	beq-	2f
+#endif
 	mtctr	r5
 	addi	r6,r3,-1
 	addi	r4,r4,-1
@@ -25,8 +27,10 @@ _GLOBAL(memcmp)
 	subf.	r3,r0,r3
 	bdnzt	2,1b
 	blr
+#ifdef CONFIG_FORTIFY_SOURCE
 2:	li	r3,0
 	blr
+#endif
 EXPORT_SYMBOL(memcmp)
 
 _GLOBAL(__clear_user)
-- 
2.13.3