diff options
authorJim Bos <jim876@xs4all.nl>2010-11-15 21:22:37 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2010-11-15 13:27:06 -0800
commit22d3243de86bc92d874abb7c5b185d5c47aba323 (patch)
parentMerge git://git.kernel.org/pub/scm/linux/kernel/git/steve/gfs2-2.6-fixes (diff)
Fix gcc 4.5.1 miscompiling drivers/char/i8k.c (again)
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 <jim876@xs4all.nl> Acked-by: Jakub Jelinek <jakub@redhat.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Andreas Schwab <schwab@linux-m68k.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 4 insertions, 4 deletions
diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
index f0863bec186f..d72433f2d310 100644
--- a/drivers/char/i8k.c
+++ b/drivers/char/i8k.c
@@ -120,7 +120,7 @@ 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"
@@ -142,11 +142,11 @@ static int i8k_smm(struct smm_regs *regs)
"shrl $8,%%eax\n\t"
"andl $1,%%eax\n"
- :"=a"(rc), "+m" (*regs)
+ :"=a"(rc)
: "a"(regs)
: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
- 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"
@@ -168,7 +168,7 @@ static int i8k_smm(struct smm_regs *regs)
"shrl $8,%%eax\n\t"
"andl $1,%%eax\n"
- :"=a"(rc), "+m" (*regs)
+ :"=a"(rc)
: "a"(regs)
: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");