On Wed, May 11, 2011 at 04:15:45PM +0200, Jean Delvare wrote: > On Wed, 11 May 2011 15:48:59 +0200, Luca Tettamanti wrote: > > On Wed, May 11, 2011 at 02:43:35PM +0200, Luca Tettamanti wrote: > > > Jeff's CPU does indeed lack lahf (see cpuinfo), so the driver should not > > > unconditionally use the intruction. > > > The driver should check X86_FEATURE_LAHF_LM or use use a different > > > method to read EFLAFS (pushf?). > > > > The driver uses lahf to copy the lowest byte of EFLAGS to eax, then > > shifts it to right and test the lowest bit (CF). > > Using pushf instead we get the whole EFLAGS and test the lowest bit. > > Does it make sense? Someone should double check the patch, I don't trust > > my assembly skills ;) > > > > diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c > > index d72433f..3554d10 100644 > > --- a/drivers/char/i8k.c > > +++ b/drivers/char/i8k.c > > @@ -139,8 +139,8 @@ static int i8k_smm(struct smm_regs *regs) > > "movl %%edi,20(%%rax)\n\t" > > "popq %%rdx\n\t" > > "movl %%edx,0(%%rax)\n\t" > > - "lahf\n\t" > > - "shrl $8,%%eax\n\t" > > + "pusfh\n\t" > > I think you meant pushf, not pusfh, right? Yeah, right... hand me that brown paper bag ;) > > > + "popl %%eax\n\t" > > "andl $1,%%eax\n" > > :"=a"(rc) > > : "a"(regs) > > I am no asm expert, but I don't get why you removed the shrl > instruction. As I understand it, your pushf+popl replaces only lahf, > the bit shifting is still needed (I assume the code wants to test bit 8 > in the flag register.) AFAIK lahf loads the lowest byte of EFLAGS into AH which is the upper half of AX, hence the shift. The popl is wrong though, pushf only pushes 2 bytes... so let's try again: diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c index d72433f..f71f266 100644 --- a/drivers/char/i8k.c +++ b/drivers/char/i8k.c @@ -139,8 +139,8 @@ static int i8k_smm(struct smm_regs *regs) "movl %%edi,20(%%rax)\n\t" "popq %%rdx\n\t" "movl %%edx,0(%%rax)\n\t" - "lahf\n\t" - "shrl $8,%%eax\n\t" + "pushf\n\t" + "pop %%ax\n\t" "andl $1,%%eax\n" :"=a"(rc) : "a"(regs) Luca _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
