Date: Mon, 25 Jul 2005 12:06:38 -0700 From: Peter Wemm <peter@wemm.org> To: freebsd-amd64@freebsd.org Cc: Kris Kennaway <kris@obsecurity.org> Subject: Re: fpudna: fpcurthread == curthread 2 times Message-ID: <200507251206.39454.peter@wemm.org> In-Reply-To: <20050411033957.GA21170@xor.obsecurity.org> References: <20050411033957.GA21170@xor.obsecurity.org>
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On Sunday 10 April 2005 08:39 pm, Kris Kennaway wrote:
> Got this on an SMP package machine running 5.4-RC2:
>
> fpudna: fpcurthread == curthread 1 times
> fpudna: fpcurthread == curthread 2 times
>
> int
> fpudna()
> {
> struct pcb *pcb;
> register_t s;
>
> if (PCPU_GET(fpcurthread) == curthread) {
> printf("fpudna: fpcurthread == curthread %d times\n",
> ++err_count);
> stop_emulating();
> return (1);
> }
>
> Debugging message accidentally left in, or bug?
>
> Kris
If any folks are reliably seeing these messages, please try a tweak to
amd64/amd64/fpu.c. The lines near the top that are "__asm()"... please
change them all to "__asm __volatile()"
This is the code that I'd like changed:
#define fldcw(addr) __asm("fldcw %0" : : "m" (*(addr)))
#define fnclex() __asm("fnclex")
#define fninit() __asm("fninit")
#define fnstcw(addr) __asm __volatile("fnstcw %0" :
"=m" (*(addr)))
#define fnstsw(addr) __asm __volatile("fnstsw %0" :
"=m" (*(addr)))
#define fxrstor(addr) __asm("fxrstor %0" : : "m" (*(addr)))
#define fxsave(addr) __asm __volatile("fxsave %0" :
"=m" (*(addr)))
#define ldmxcsr(r) __asm __volatile("ldmxcsr %0" : :
"m" (r))
#define start_emulating() __asm("smsw %%ax; orb %0,%%al; lmsw
%%ax" \
: : "n" (CR0_TS) : "ax")
#define stop_emulating() __asm("clts")
If this tweak has any effect (either better or worse), please let me
know. I'm wondering if there are some reordering effects going on
here.
It is just a wild shot in the dark. It won't hurt anything though and
is safe to try. Most likely it is a wild goose chase, but it could be
worth a try.
What would be worth knowing is: 1) if the patch stops messages for
people who see them regularly or repeatably, and/or 2) if the messages
keep happening even with the patch applied. The latter case indicates
that it is a wild goose chase.
--
Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5
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