> That said, changing the inline asm to just clobber one less register
> would be completely sufficient to make it work well with all gccs out there,
> just push/pop one of the register around the whole body. I doubt calling
> out SMM BIOS is actually so performance critical that one push and one pop
> would ruin it. Of course x86_64 version can stay as is, there are enough
> registers left...
Yes traditionally clobbering all registers has been dangerous
and it clearly can be done inside the asm too.
Here's a untested patch to do some manual push/pops too. Could someone with
the hardware please test it? (running a 32bit kernel)
-Andi
---
i8k: Clobber less registers
gcc doesn't like inline assembler statements that clobber nearly
all registers. Save a few registers manually on i386 to avoid this
problem.
Fix suggested by Jakub Jelinek
Signed-off-by: Andi Kleen <a...@linux.intel.com>
diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
index f0863be..a2da38b 100644
--- a/drivers/char/i8k.c
+++ b/drivers/char/i8k.c
@@ -146,7 +146,10 @@ static int i8k_smm(struct smm_regs *regs)
: "a"(regs)
: "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
#else
- asm("pushl %%eax\n\t"
+ asm("pushl %%ebx\n\t"
+ "pushl %%ecx\n\t"
+ "pushl %%edx\n\t"
+ "pushl %%eax\n\t"
"movl 0(%%eax),%%edx\n\t"
"push %%edx\n\t"
"movl 4(%%eax),%%ebx\n\t"
@@ -167,10 +170,13 @@ 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"
+ "andl $1,%%eax\n\t"
+ "popl %%edx\n\t"
+ "popl %%ecx\n\t"
+ "popl %%ebx\n"
:"=a"(rc), "+m" (*regs)
: "a"(regs)
- : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
+ : "%esi", "%edi", "memory");
#endif
if (rc != 0 || (regs->eax & 0xffff) == 0xffff || regs->eax == eax)
return -EINVAL;
--
a...@linux.intel.com -- Speaking for myself only.
