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arm64: head.S: use memset to clear BSS 

Currently we use an open-coded memzero to clear the BSS. As it is a
trivial implementation, it is sub-optimal.

Our optimised memset doesn't use the stack, is position-independent, and
for the memzero case can use of DC ZVA to clear large blocks
efficiently. In __mmap_switched the MMU is on and there are no live
caller-saved registers, so we can safely call an uninstrumented memset.

This patch changes __mmap_switched to use memset when clearing the BSS.
We use the __pi_memset alias so as to avoid any instrumentation in all
kernel configurations.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Mark Rutland 2016-01-06 11:05:27 +00:00 committed by Will Deacon
parent b523e185bb
commit 2a803c4db6
1 changed files with 6 additions and 7 deletions
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13
arch/arm64/kernel/head.S
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@ -415,14 +415,13 @@ ENDPROC(__create_page_tables)
*/
.set initial_sp, init_thread_union + THREAD_START_SP
__mmap_switched:
adr_l x6, __bss_start
adr_l x7, __bss_stop
// Clear BSS
adr_l x0, __bss_start
mov x1, xzr
adr_l x2, __bss_stop
sub x2, x2, x0
bl __pi_memset
1: cmp x6, x7
b.hs 2f
str xzr, [x6], #8 // Clear BSS
b 1b
2:
adr_l sp, initial_sp, x4
mov x4, sp
and x4, x4, #~(THREAD_SIZE - 1)