From d6bd8194e2867e85ac2de63486d3b83ccfae4e62 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Mon, 26 Jun 2017 11:30:57 +1000 Subject: [PATCH] powerpc/32: Avoid miscompilation w/GCC 4.6.3 - don't inline copy_to/from_user() Larry Finger reported that his Powerbook G4 was no longer booting with v4.12-rc, userspace was up but giving weird errors such as: udevd[64]: starting version 175 udevd[64]: Unable to receive ctrl message: Bad address. modprobe: chdir(4.12-rc1): No such file or directory He bisected the problem to commit 3448890c32c3 ("powerpc: get rid of zeroing, switch to RAW_COPY_USER"). Al identified that the problem is actually a miscompilation by GCC 4.6.3, which is exposed by the above commit. Al also pointed out that inlining copy_to/from_user() is probably of little or no benefit, which is correct. Using Anton's copy_to_user benchmark, with a pathological single byte copy, we see a small increase in performance by *removing* inlining: Before (inlined): # time ./copy_to_user -w -l 1 -i 10000000 ( x 3 ) real 0m22.063s real 0m22.059s real 0m22.076s After: # time ./copy_to_user -w -l 1 -i 10000000 ( x 3 ) real 0m21.325s real 0m21.299s real 0m21.364s So as a small performance improvement and to avoid the miscompilation, drop inlining copy_to/from_user() on 32-bit. Fixes: 3448890c32c3 ("powerpc: get rid of zeroing, switch to RAW_COPY_USER") Reported-by: Larry Finger Suggested-by: Al Viro Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/uaccess.h | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h index 5c0d8a8cdae5..41e88d3ce36b 100644 --- a/arch/powerpc/include/asm/uaccess.h +++ b/arch/powerpc/include/asm/uaccess.h @@ -267,13 +267,7 @@ do { \ extern unsigned long __copy_tofrom_user(void __user *to, const void __user *from, unsigned long size); -#ifndef __powerpc64__ - -#define INLINE_COPY_FROM_USER -#define INLINE_COPY_TO_USER - -#else /* __powerpc64__ */ - +#ifdef __powerpc64__ static inline unsigned long raw_copy_in_user(void __user *to, const void __user *from, unsigned long n) {