Date: Thu, 3 Jun 2004 10:20:15 +1000 From: Tim Robbins <tim@robbins.dropbear.id.au> To: David Schultz <das@freebsd.org> Cc: amd64@freebsd.org Subject: Re: Initial FP exception flags incorrect on amd64 Message-ID: <20040603002015.GA14544@cat.robbins.dropbear.id.au> In-Reply-To: <20040602064846.GA6124@VARK.homeunix.com> References: <20040602064846.GA6124@VARK.homeunix.com>
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On Tue, Jun 01, 2004 at 11:48:46PM -0700, David Schultz wrote:
> I discovered that new processes on amd64 have the inexact flag
> raised by default, at least on sledge. However, all the sticky
> flags should be clear initially.
[...]
> I don't have any amd64 hardware of my own to test kernel patches
> on, but if I were to make a wild guess as to how to solve the
> problem, it would be the following patch. I would appreciate it
> if someone could address the problem, or at least let me know
> whether my proposed fix works.
>
> Index: sys/amd64/amd64/fpu.c
> ===================================================================
> RCS file: /cvs/src/sys/amd64/amd64/fpu.c,v
> retrieving revision 1.149
> diff -u -r1.149 fpu.c
> --- fpu.c 5 Apr 2004 21:25:51 -0000 1.149
> +++ fpu.c 2 Jun 2004 06:08:34 -0000
> @@ -73,6 +73,7 @@
> #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 stmxcsr(addr) __asm("stmxcsr %0" : "=m" (*(addr)))
> #define start_emulating() __asm("smsw %%ax; orb %0,%%al; lmsw %%ax" \
> : : "n" (CR0_TS) : "ax")
> #define stop_emulating() __asm("clts")
> @@ -119,6 +120,8 @@
> fninit();
> control = __INITIAL_FPUCW__;
> fldcw(&control);
> + control = __INITIAL_MXCSR__;
> + stmxcsr(&control);
> fxsave(&fpu_cleanstate);
> start_emulating();
> fpu_cleanstate_ready = 1;
This seems to cause a panic (trap 12) on startup. Shouldn't it be ldmxcsr
instead? Changing that causes a different kind of panic (trap 9.)
Tim
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