This is a note to let you know that I've just added the patch titled
Fix gcc 4.5.1 miscompiling drivers/char/i8k.c (again)
to the 2.6.33-longterm tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/longterm/longterm-queue-2.6.33.git;a=summary
The filename of the patch is:
fix-gcc-4.5.1-miscompiling-drivers-char-i8k.c-again.patch
and it can be found in the queue-2.6.33 subdirectory.
If you, or anyone else, feels it should not be added to the 2.6.33 longterm
tree,
please let <[email protected]> know about it.
>From 22d3243de86bc92d874abb7c5b185d5c47aba323 Mon Sep 17 00:00:00 2001
From: Jim Bos <[email protected]>
Date: Mon, 15 Nov 2010 21:22:37 +0100
Subject: Fix gcc 4.5.1 miscompiling drivers/char/i8k.c (again)
From: Jim Bos <[email protected]>
commit 22d3243de86bc92d874abb7c5b185d5c47aba323 upstream.
The fix in commit 6b4e81db2552 ("i8k: Tell gcc that *regs gets
clobbered") to work around the gcc miscompiling i8k.c to add "+m
(*regs)" caused register pressure problems and a build failure.
Changing the 'asm' statement to 'asm volatile' instead should prevent
that and works around the gcc bug as well, so we can remove the "+m".
[ Background on the gcc bug: a memory clobber fails to mark the function
the asm resides in as non-pure (aka "__attribute__((const))"), so if
the function does nothing else that triggers the non-pure logic, gcc
will think that that function has no side effects at all. As a result,
callers will be mis-compiled.
Adding the "+m" made gcc see that it's not a pure function, and so
does "asm volatile". The problem was never really the need to mark
"*regs" as changed, since the memory clobber did that part - the
problem was just a bug in the gcc "pure" function analysis - Linus ]
Signed-off-by: Jim Bos <[email protected]>
Acked-by: Jakub Jelinek <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Andreas Schwab <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/char/i8k.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/drivers/char/i8k.c
+++ b/drivers/char/i8k.c
@@ -119,7 +119,7 @@ static int i8k_smm(struct smm_regs *regs
int eax = regs->eax;
#if defined(CONFIG_X86_64)
- asm("pushq %%rax\n\t"
+ asm volatile("pushq %%rax\n\t"
"movl 0(%%rax),%%edx\n\t"
"pushq %%rdx\n\t"
"movl 4(%%rax),%%ebx\n\t"
@@ -141,11 +141,11 @@ static int i8k_smm(struct smm_regs *regs
"lahf\n\t"
"shrl $8,%%eax\n\t"
"andl $1,%%eax\n"
- :"=a"(rc), "+m" (*regs)
+ :"=a"(rc)
: "a"(regs)
: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
#else
- asm("pushl %%eax\n\t"
+ asm volatile("pushl %%eax\n\t"
"movl 0(%%eax),%%edx\n\t"
"push %%edx\n\t"
"movl 4(%%eax),%%ebx\n\t"
@@ -167,7 +167,7 @@ static int i8k_smm(struct smm_regs *regs
"lahf\n\t"
"shrl $8,%%eax\n\t"
"andl $1,%%eax\n"
- :"=a"(rc), "+m" (*regs)
+ :"=a"(rc)
: "a"(regs)
: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
#endif
Patches currently in longterm-queue-2.6.33 which might be from [email protected]
are
/home/gregkh/linux/longterm/longterm-queue-2.6.33/queue-2.6.33/fix-gcc-4.5.1-miscompiling-drivers-char-i8k.c-again.patch
/home/gregkh/linux/longterm/longterm-queue-2.6.33/queue-2.6.33/i8k-tell-gcc-that-regs-gets-clobbered.patch
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