From 6b4e81db2552bad04100e7d5ddeed7e848f53b48 Mon Sep 17 00:00:00 2001 From: Jim Bos Date: Sat, 13 Nov 2010 12:13:53 +0100 Subject: i8k: Tell gcc that *regs gets clobbered More recent GCC caused the i8k driver to stop working, on Slackware compiler was upgraded from gcc-4.4.4 to gcc-4.5.1 after which it didn't work anymore, meaning the driver didn't load or gave total nonsensical output. As it turned out the asm(..) statement forgot to mention it modifies the *regs variable. Credits to Andi Kleen and Andreas Schwab for providing the fix. Signed-off-by: Jim Bos Cc: Andi Kleen Cc: Andreas Schwab Signed-off-by: Linus Torvalds --- drivers/char/i8k.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'drivers/char/i8k.c') diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c index 3bc0eef..f0863be 100644 --- a/drivers/char/i8k.c +++ b/drivers/char/i8k.c @@ -142,7 +142,7 @@ static int i8k_smm(struct smm_regs *regs) "lahf\n\t" "shrl $8,%%eax\n\t" "andl $1,%%eax\n" - :"=a"(rc) + :"=a"(rc), "+m" (*regs) : "a"(regs) : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory"); #else @@ -167,7 +167,8 @@ static int i8k_smm(struct smm_regs *regs) "movl %%edx,0(%%eax)\n\t" "lahf\n\t" "shrl $8,%%eax\n\t" - "andl $1,%%eax\n":"=a"(rc) + "andl $1,%%eax\n" + :"=a"(rc), "+m" (*regs) : "a"(regs) : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory"); #endif -- cgit v1.1 From 22d3243de86bc92d874abb7c5b185d5c47aba323 Mon Sep 17 00:00:00 2001 From: Jim Bos Date: Mon, 15 Nov 2010 21:22:37 +0100 Subject: 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 Acked-by: Jakub Jelinek Cc: Andi Kleen Cc: Andreas Schwab Signed-off-by: Linus Torvalds --- drivers/char/i8k.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'drivers/char/i8k.c') diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c index f0863be..d72433f 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) "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" @@ -168,7 +168,7 @@ 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 -- cgit v1.1