[PATCH] ARM: get rid of __memzero()
Nicolas Pitre
nicolas.pitre at linaro.org
Thu Jan 18 19:53:38 PST 2018
The __memzero assembly code is almost identical to memset's except for
two orr instructions. The runtime performance of __memset(p, n) and
memset(p, 0, n) is accordingly almost identical.
However, the memset() macro used to guard against a zero length and to
call __memzero at compile time when the fill value is a constant zero
interferes with compiler optimizations.
Arnd found tha the test against a zero length brings up some new
warnings with gcc v8:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82103
And successively rremoving the test against a zero length and the call
to __memzero optimization produces the following kernel sizes for
defconfig with gcc 6:
text data bss dec hex filename
12248142 6278960 413588 18940690 1210312 vmlinux.orig
12244474 6278960 413588 18937022 120f4be vmlinux.no_zero_test
12239160 6278960 413588 18931708 120dffc vmlinux.no_memzero
So it is probably not worth keeping __memzero around given that the
compiler can do a better job at inlining trivial memset(p,0,n) on its
own. And the memset code already handles a zero length just fine.
Suggested-by: Arnd Bergmann <arnd at arndb.de>
Signed-off-by: Nicolas Pitre <nico at linaro.org>
diff --git a/arch/arm/boot/compressed/string.c b/arch/arm/boot/compressed/string.c
index 309e1bbad7..13c90abc68 100644
--- a/arch/arm/boot/compressed/string.c
+++ b/arch/arm/boot/compressed/string.c
@@ -130,8 +130,3 @@ void *memset(void *s, int c, size_t count)
*xs++ = c;
return s;
}
-
-void __memzero(void *s, size_t count)
-{
- memset(s, 0, count);
-}
diff --git a/arch/arm/include/asm/string.h b/arch/arm/include/asm/string.h
index f54a3136aa..111a1d8a41 100644
--- a/arch/arm/include/asm/string.h
+++ b/arch/arm/include/asm/string.h
@@ -39,18 +39,4 @@ static inline void *memset64(uint64_t *p, uint64_t v, __kernel_size_t n)
return __memset64(p, v, n * 8, v >> 32);
}
-extern void __memzero(void *ptr, __kernel_size_t n);
-
-#define memset(p,v,n) \
- ({ \
- void *__p = (p); size_t __n = n; \
- if ((__n) != 0) { \
- if (__builtin_constant_p((v)) && (v) == 0) \
- __memzero((__p),(__n)); \
- else \
- memset((__p),(v),(__n)); \
- } \
- (__p); \
- })
-
#endif
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
index 5266fd9ad6..783fbb4de5 100644
--- a/arch/arm/kernel/armksyms.c
+++ b/arch/arm/kernel/armksyms.c
@@ -92,7 +92,6 @@ EXPORT_SYMBOL(__memset64);
EXPORT_SYMBOL(memcpy);
EXPORT_SYMBOL(memmove);
EXPORT_SYMBOL(memchr);
-EXPORT_SYMBOL(__memzero);
EXPORT_SYMBOL(mmioset);
EXPORT_SYMBOL(mmiocpy);
diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
index 21dde771a7..d7eb3c4db5 100644
--- a/arch/arm/kernel/head-common.S
+++ b/arch/arm/kernel/head-common.S
@@ -105,8 +105,9 @@ __mmap_switched:
ARM( ldmia r4!, {r0, r1, sp} )
THUMB( ldmia r4!, {r0, r1, r3} )
THUMB( mov sp, r3 )
- sub r1, r1, r0
- bl __memzero @ clear .bss
+ sub r2, r1, r0
+ mov r1, #0
+ bl memset @ clear .bss
ldmia r4, {r0, r1, r2, r3}
str r9, [r0] @ Save processor ID
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 4cb0b9624d..ad25fd1872 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -8,7 +8,7 @@
lib-y := backtrace.o changebit.o csumipv6.o csumpartial.o \
csumpartialcopy.o csumpartialcopyuser.o clearbit.o \
delay.o delay-loop.o findbit.o memchr.o memcpy.o \
- memmove.o memset.o memzero.o setbit.o \
+ memmove.o memset.o setbit.o \
strchr.o strrchr.o \
testchangebit.o testclearbit.o testsetbit.o \
ashldi3.o ashrdi3.o lshrdi3.o muldi3.o \
diff --git a/arch/arm/lib/memzero.S b/arch/arm/lib/memzero.S
deleted file mode 100644
index 0eded952e0..0000000000
--- a/arch/arm/lib/memzero.S
+++ /dev/null
@@ -1,137 +0,0 @@
-/*
- * linux/arch/arm/lib/memzero.S
- *
- * Copyright (C) 1995-2000 Russell King
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- */
-#include <linux/linkage.h>
-#include <asm/assembler.h>
-#include <asm/unwind.h>
-
- .text
- .align 5
- .word 0
-/*
- * Align the pointer in r0. r3 contains the number of bytes that we are
- * mis-aligned by, and r1 is the number of bytes. If r1 < 4, then we
- * don't bother; we use byte stores instead.
- */
-UNWIND( .fnstart )
-1: subs r1, r1, #4 @ 1 do we have enough
- blt 5f @ 1 bytes to align with?
- cmp r3, #2 @ 1
- strltb r2, [r0], #1 @ 1
- strleb r2, [r0], #1 @ 1
- strb r2, [r0], #1 @ 1
- add r1, r1, r3 @ 1 (r1 = r1 - (4 - r3))
-/*
- * The pointer is now aligned and the length is adjusted. Try doing the
- * memzero again.
- */
-
-ENTRY(__memzero)
- mov r2, #0 @ 1
- ands r3, r0, #3 @ 1 unaligned?
- bne 1b @ 1
-/*
- * r3 = 0, and we know that the pointer in r0 is aligned to a word boundary.
- */
- cmp r1, #16 @ 1 we can skip this chunk if we
- blt 4f @ 1 have < 16 bytes
-
-#if ! CALGN(1)+0
-
-/*
- * We need an extra register for this loop - save the return address and
- * use the LR
- */
- str lr, [sp, #-4]! @ 1
-UNWIND( .fnend )
-UNWIND( .fnstart )
-UNWIND( .save {lr} )
- mov ip, r2 @ 1
- mov lr, r2 @ 1
-
-3: subs r1, r1, #64 @ 1 write 32 bytes out per loop
- stmgeia r0!, {r2, r3, ip, lr} @ 4
- stmgeia r0!, {r2, r3, ip, lr} @ 4
- stmgeia r0!, {r2, r3, ip, lr} @ 4
- stmgeia r0!, {r2, r3, ip, lr} @ 4
- bgt 3b @ 1
- ldmeqfd sp!, {pc} @ 1/2 quick exit
-/*
- * No need to correct the count; we're only testing bits from now on
- */
- tst r1, #32 @ 1
- stmneia r0!, {r2, r3, ip, lr} @ 4
- stmneia r0!, {r2, r3, ip, lr} @ 4
- tst r1, #16 @ 1 16 bytes or more?
- stmneia r0!, {r2, r3, ip, lr} @ 4
- ldr lr, [sp], #4 @ 1
-UNWIND( .fnend )
-
-#else
-
-/*
- * This version aligns the destination pointer in order to write
- * whole cache lines at once.
- */
-
- stmfd sp!, {r4-r7, lr}
-UNWIND( .fnend )
-UNWIND( .fnstart )
-UNWIND( .save {r4-r7, lr} )
- mov r4, r2
- mov r5, r2
- mov r6, r2
- mov r7, r2
- mov ip, r2
- mov lr, r2
-
- cmp r1, #96
- andgts ip, r0, #31
- ble 3f
-
- rsb ip, ip, #32
- sub r1, r1, ip
- movs ip, ip, lsl #(32 - 4)
- stmcsia r0!, {r4, r5, r6, r7}
- stmmiia r0!, {r4, r5}
- movs ip, ip, lsl #2
- strcs r2, [r0], #4
-
-3: subs r1, r1, #64
- stmgeia r0!, {r2-r7, ip, lr}
- stmgeia r0!, {r2-r7, ip, lr}
- bgt 3b
- ldmeqfd sp!, {r4-r7, pc}
-
- tst r1, #32
- stmneia r0!, {r2-r7, ip, lr}
- tst r1, #16
- stmneia r0!, {r4-r7}
- ldmfd sp!, {r4-r7, lr}
-UNWIND( .fnend )
-
-#endif
-
-UNWIND( .fnstart )
-4: tst r1, #8 @ 1 8 bytes or more?
- stmneia r0!, {r2, r3} @ 2
- tst r1, #4 @ 1 4 bytes or more?
- strne r2, [r0], #4 @ 1
-/*
- * When we get here, we've got less than 4 bytes to zero. We
- * may have an unaligned pointer as well.
- */
-5: tst r1, #2 @ 1 2 bytes or more?
- strneb r2, [r0], #1 @ 1
- strneb r2, [r0], #1 @ 1
- tst r1, #1 @ 1 a byte left over
- strneb r2, [r0], #1 @ 1
- ret lr @ 1
-UNWIND( .fnend )
-ENDPROC(__memzero)
diff --git a/drivers/dma/imx-dma.c b/drivers/dma/imx-dma.c
index 331f863c60..715b39ae5a 100644
--- a/drivers/dma/imx-dma.c
+++ b/drivers/dma/imx-dma.c
@@ -765,7 +765,7 @@ static int imxdma_alloc_chan_resources(struct dma_chan *chan)
desc = kzalloc(sizeof(*desc), GFP_KERNEL);
if (!desc)
break;
- __memzero(&desc->desc, sizeof(struct dma_async_tx_descriptor));
+ memset(&desc->desc, 0, sizeof(struct dma_async_tx_descriptor));
dma_async_tx_descriptor_init(&desc->desc, chan);
desc->desc.tx_submit = imxdma_tx_submit;
/* txd.flags will be overwritten in prep funcs */
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