Messages in this thread | | | Date | Fri, 1 Aug 2008 00:11:45 +0200 | From | Willy Tarreau <> | Subject | Re: [PATCH] x86: fdiv bug detection fix |
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On Thu, Jul 31, 2008 at 02:49:20PM -0700, Andrew Morton wrote: > On Thu, 31 Jul 2008 23:43:44 +0200 > Krzysztof Helt <krzysztof.h1@wp.pl> wrote: > > > From: Krzysztof Helt <krzysztof.h1@wp.pl> > > > > The fdiv detection code writes s32 integer into > > the boot_cpu_data.fdiv_bug. > > However, the boot_cpu_data.fdiv_bug is only char (s8) > > field so the detection overwrites already set fields for > > other bugs, e.g. the f00f bug field. > > > > Use local s32 variable to receive result. > > > > Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl> > > --- > > > > This is a partial fix to Bugzilla #9928 - fixes wrong > > information about the f00f bug (tested) and probably > > for coma bug (I have no cpu to test this). > > > > diff -urp linux-alsa/arch/x86/kernel/cpu/bugs.c linux-new/arch/x86/kernel/cpu/bugs.c > > --- linux-alsa/arch/x86/kernel/cpu/bugs.c 2008-07-31 12:40:31.000000000 +0200 > > +++ linux-new/arch/x86/kernel/cpu/bugs.c 2008-07-31 23:24:07.722657435 +0200 > > @@ -50,6 +50,8 @@ static double __initdata y = 3145727.0; > > */ > > static void __init check_fpu(void) > > { > > + s32 fdiv_bug; > > + > > if (!boot_cpu_data.hard_math) { > > #ifndef CONFIG_MATH_EMULATION > > printk(KERN_EMERG "No coprocessor found and no math emulation present.\n"); > > @@ -74,8 +76,10 @@ static void __init check_fpu(void) > > "fistpl %0\n\t" > > "fwait\n\t" > > "fninit" > > - : "=m" (*&boot_cpu_data.fdiv_bug) > > + : "=m" (*&fdiv_bug) > > : "m" (*&x), "m" (*&y)); > > + > > + boot_cpu_data.fdiv_bug = fdiv_bug; > > if (boot_cpu_data.fdiv_bug) > > printk("Hmm, FPU with FDIV bug.\n"); > > } > > hm, the code seems to have been that way for quite some time.
Indeed! since boot_cpu_data.fdiv_bug was declared as an int in 2.4, I think it might have changed when a lot of code was moved from asm/*.h to arch/*.c.
> I wonder why nobody noticed this before.
For the same reason those bugs were noticed very late in the products' lifetime I guess : because unless someone actively plays with them on your machine, you hardly trigger them by accident.
Willy
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