From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Wed, 6 Jan 2016 11:05:27 +0000 Subject: [PATCH 2/2] arm64: use memset to clear BSS In-Reply-To: <1452078327-9635-1-git-send-email-mark.rutland@arm.com> References: <1452078327-9635-1-git-send-email-mark.rutland@arm.com> Message-ID: <1452078327-9635-2-git-send-email-mark.rutland@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. As with the head symbols, we must get the linker to generate __bss_size, as there is no ELF relocation for the subtraction of two symbols. Signed-off-by: Mark Rutland Cc: Ard Biesheuvel Cc: Catalin Marinas Cc: Marc Zyngier Cc: Will Deacon --- arch/arm64/kernel/head.S | 14 ++++++-------- arch/arm64/kernel/image.h | 2 ++ 2 files changed, 8 insertions(+), 8 deletions(-) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 23cfc08..247a97b 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -415,14 +415,12 @@ 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 + mov_l x2, __bss_size + bl __pi_memset + adr_l sp, initial_sp, x4 str_l x21, __fdt_pointer, x5 // Save FDT pointer str_l x24, memstart_addr, x6 // Save PHYS_OFFSET diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h index bc2abb8..5fd76b5 100644 --- a/arch/arm64/kernel/image.h +++ b/arch/arm64/kernel/image.h @@ -95,4 +95,6 @@ __efistub__edata = _edata; #endif +__bss_size = __bss_stop - __bss_start; + #endif /* __ASM_IMAGE_H */ -- 1.9.1