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fix i8k inline asm to avoid miscompilation with newer gcc

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This commit is contained in:
Kyle McMartin 2010-11-23 09:50:52 -05:00
parent 15589b25c9
commit 6b5e37dd4b
2 changed files with 92 additions and 0 deletions
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fix-i8k-inline-asm.patch Normal file
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@ -0,0 +1,84 @@
commit 22d3243de86bc92d874abb7c5b185d5c47aba323
Author: Jim Bos <jim876@xs4all.nl>
Date: Mon Nov 15 21:22:37 2010 +0100
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>
commit 6b4e81db2552bad04100e7d5ddeed7e848f53b48
Author: Jim Bos <jim876@xs4all.nl>
Date: Sat Nov 13 12:13:53 2010 +0100
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 <jim876@xs4all.nl>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
index 3bc0eef..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"
@@ -146,7 +146,7 @@ static int i8k_smm(struct smm_regs *regs)
: "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 +167,8 @@ 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)
: "a"(regs)
: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
#endif

8
kernel.spec
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@ -728,6 +728,8 @@ Patch12305: xhci_hcd-suspend-resume.patch
Patch12307: tty-restore-tty_ldisc_wait_idle.patch
Patch12308: fix-i8k-inline-asm.patch
%endif
BuildRoot: %{_tmppath}/kernel-%{KVERREL}-root
@ -1350,6 +1352,8 @@ ApplyPatch xhci_hcd-suspend-resume.patch
ApplyPatch tty-restore-tty_ldisc_wait_idle.patch
ApplyPatch fix-i8k-inline-asm.patch
# END OF PATCH APPLICATIONS
%endif
@ -1963,6 +1967,10 @@ fi
# || ||
%changelog
* Tue Nov 23 2010 Kyle McMartin <kyle@redhat.com>
- fix-i8k-inline-asm.patch: backport gcc miscompilation fix from git
[22d3243d, 6b4e81db] (rhbz#647677)
* Mon Nov 22 2010 Kyle McMartin <kyle@redhat.com>
- Add a debugging patch to help track down which tty is being
poked by plymouth.