[PATCH 8/8] arm64: Rewrite __arch_clear_user()
From: Robin Murphy <robin.murphy@arm.com>
Date: 2021-05-11 16:22:27
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
Now that we're always using STTR variants rather than abstracting two different addressing modes, the user_ldst macro here is frankly more obfuscating than helpful. Rewrite __arch_clear_user() with regular USER() annotations so that it's clearer what's going on, and take the opportunity to minimise the branchiness in the most common paths, which also allows the exception fixup to return a more accurate result. Signed-off-by: Robin Murphy <robin.murphy@arm.com> --- arch/arm64/lib/clear_user.S | 42 +++++++++++++++++++------------------ 1 file changed, 22 insertions(+), 20 deletions(-)
diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index af9afcbec92c..1005345b4066 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S@@ -1,12 +1,9 @@ /* SPDX-License-Identifier: GPL-2.0-only */ /* - * Based on arch/arm/lib/clear_user.S - * - * Copyright (C) 2012 ARM Ltd. + * Copyright (C) 2021 Arm Ltd. */ -#include <linux/linkage.h> -#include <asm/asm-uaccess.h> +#include <linux/linkage.h> #include <asm/assembler.h> .text
@@ -19,25 +16,30 @@ * * Alignment fixed up by hardware. */ + .p2align 4 SYM_FUNC_START(__arch_clear_user) - mov x2, x1 // save the size for fixup return + add x2, x0, x1 subs x1, x1, #8 b.mi 2f 1: -user_ldst 9f, sttr, xzr, x0, 8 +USER(9f, sttr xzr, [x0]) + add x0, x0, #8 subs x1, x1, #8 - b.pl 1b -2: adds x1, x1, #4 - b.mi 3f -user_ldst 9f, sttr, wzr, x0, 4 - sub x1, x1, #4 -3: adds x1, x1, #2 - b.mi 4f -user_ldst 9f, sttrh, wzr, x0, 2 - sub x1, x1, #2 -4: adds x1, x1, #1 - b.mi 5f -user_ldst 9f, sttrb, wzr, x0, 0 + b.hi 1b +USER(9f, sttr xzr, [x2, #-8]) + mov x0, #0 + ret + +2: tbz x1, #2, 3f +USER(9f, sttr wzr, [x0]) +USER(9f, sttr wzr, [x2, #-4]) + mov x0, #0 + ret + +3: tbz x1, #1, 4f +USER(9f, sttrh wzr, [x0]) +4: tbz x1, #0, 5f +USER(9f, sttrb wzr, [x2, #-1]) 5: mov x0, #0 ret SYM_FUNC_END(__arch_clear_user)
@@ -45,6 +47,6 @@ EXPORT_SYMBOL(__arch_clear_user) .section .fixup,"ax" .align 2 -9: mov x0, x2 // return the original size +9: sub x0, x2, x0 ret .previous
--
2.21.0.dirty
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