[PATCH] powerpc/32: Avoid miscompilation w/GCC 4.6.3 - don't inline copy_to/from_user()

[Michael Ellerman]

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 <Larry.Finger at lwfinger.net>
Suggested-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
---
 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)
 {
-- 
2.7.4