ARM: 8745/1: get rid of __memzero() (ff5fdafc) · Commits · 戴 / test

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@arndb.de> Signed-off-by:

Nicolas Pitre <nico@linaro.org> Acked-by:

Ard Biesheuvel <ard.biesheuvel@linaro.org> Acked-by:

Arnd Bergmann <arnd@arndb.de> Signed-off-by:

Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/boot/compressed/string.c

+0 −5

Original line number	Diff line number	Diff line
		@@ -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);
		}

arch/arm/include/asm/string.h

+0 −14

Original line number	Diff line number	Diff line
		@@ -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

arch/arm/kernel/armksyms.c

+0 −1

Original line number	Diff line number	Diff line
		@@ -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);

arch/arm/kernel/head-common.S

+3 −2

Original line number	Diff line number	Diff line
		@@ -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

arch/arm/lib/Makefile

+1 −1

Original line number	Diff line number	Diff line
		@@ -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 \

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