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| author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2018-01-19 20:17:46 +0300 |
|---|---|---|
| committer | Russell King <rmk+kernel@armlinux.org.uk> | 2018-01-21 18:37:56 +0300 |
| commit | ff5fdafc9e9702846480e0cea55ba861f72140a2 (patch) | |
| tree | 28531d5acbc851bf5f210062bc9d0e08f1fee85e /arch/arm/kernel | |
| parent | ec80eb467171b511635b9e3086fec357f79afe3b (diff) | |
| download | linux-ff5fdafc9e9702846480e0cea55ba861f72140a2.tar.xz | |
ARM: 8745/1: get rid of __memzero()
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>
Diffstat (limited to 'arch/arm/kernel')
| -rw-r--r-- | arch/arm/kernel/armksyms.c | 1 | ||||
| -rw-r--r-- | arch/arm/kernel/head-common.S | 5 |
2 files changed, 3 insertions, 3 deletions
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c index 5266fd9ad6b4..783fbb4de5f9 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 21dde771a7dd..6e0375e7db05 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 |