From 2a803c4db615d85126c5c7afd5849a3cfde71422 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Wed, 6 Jan 2016 11:05:27 +0000 Subject: [PATCH] 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 Cc: Marc Zyngier Reviewed-by: Ard Biesheuvel Signed-off-by: Mark Rutland Signed-off-by: Will Deacon --- arch/arm64/kernel/head.S | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index b363f340f2c7..ffe9c2b6431b 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -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 - -1: cmp x6, x7 - b.hs 2f - str xzr, [x6], #8 // Clear BSS - b 1b -2: + // Clear BSS + adr_l x0, __bss_start + mov x1, xzr + adr_l x2, __bss_stop + sub x2, x2, x0 + bl __pi_memset + adr_l sp, initial_sp, x4 mov x4, sp and x4, x4, #~(THREAD_SIZE - 1) -- 2.20.1