Linus Torvalds wrote:
>
> On Fri, 19 Apr 2002, Brian Gerst wrote:
>
>>Here's a patch to do just that. It initializes the saved state in the
>>task struct and falls through to restore_fpu().
>
>
> One issue is whether we _can_ restore a "generated" image like this: it's
> entirely possible that Intel might save away internal CPU shadow data in
> the save-state structure, and future CPU's might be unhappy about loading
> data that doesn't conform to what the CPU would save.
>
> That said, the same issue is certainly true for just doing "xorps", since
> that will not clear any potential future CPU state.
>
> I get this feeling that Intel screwed up on specifying how to initialize
> this whole state.
>
> Linus
>
I don't know about Intel, but the Athlon doesn't appear to save anything
in the "reserved" areas. The values that I use to initialize the state
are from what is saved after loading the stack with zeroes (fldz) and
then doing finit. I have samples of the saved state from a P2, a K6-2,
and an Athlon XP.
Attached is a revised patch. I had the cpu_has_xmm test wrong.
--Brian Gerst
diff -urN linux-2.5.8/arch/i386/kernel/i387.c linux/arch/i386/kernel/i387.c --- linux-2.5.8/arch/i386/kernel/i387.c Thu Mar 7 21:18:32 2002 +++ linux/arch/i386/kernel/i387.c Fri Apr 19 19:35:14 2002 @@ -31,13 +31,21 @@ * value at reset if we support XMM instructions and then * remeber the current task has used the FPU. */ -void init_fpu(void) +void init_fpu(struct task_struct *tsk) { - __asm__("fninit"); - if ( cpu_has_xmm ) - load_mxcsr(0x1f80); - - current->used_math = 1; + if (cpu_has_fxsr) { + memset(&tsk->thread.i387.fxsave, 0, sizeof(struct i387_fxsave_struct)); + tsk->thread.i387.fxsave.cwd = 0x37f; + if (cpu_has_xmm) + tsk->thread.i387.fxsave.mxcsr = 0x1f80; + } else { + memset(&tsk->thread.i387.fsave, 0, sizeof(struct i387_fsave_struct)); + tsk->thread.i387.fsave.cwd = 0xffff037f; + tsk->thread.i387.fsave.swd = 0xffff0000; + tsk->thread.i387.fsave.twd = 0xffffffff; + tsk->thread.i387.fsave.fos = 0xffff0000; + } + tsk->used_math = 1; } /* diff -urN linux-2.5.8/arch/i386/kernel/traps.c linux/arch/i386/kernel/traps.c --- linux-2.5.8/arch/i386/kernel/traps.c Sun Apr 14 23:48:18 2002 +++ linux/arch/i386/kernel/traps.c Fri Apr 19 18:22:12 2002 @@ -757,13 +757,12 @@ */ asmlinkage void math_state_restore(struct pt_regs regs) { + struct task_struct *tsk = current; clts(); /* Allow maths ops (or we recurse) */ - if (current->used_math) { - restore_fpu(current); - } else { - init_fpu(); - } + if (!tsk->used_math) + init_fpu(tsk); + restore_fpu(tsk); set_thread_flag(TIF_USEDFPU); /* So we fnsave on switch_to() */ } diff -urN linux-2.5.8/include/asm-i386/i387.h linux/include/asm-i386/i387.h --- linux-2.5.8/include/asm-i386/i387.h Fri Apr 19 18:44:48 2002 +++ linux/include/asm-i386/i387.h Fri Apr 19 19:34:03 2002 @@ -17,7 +17,7 @@ #include <asm/sigcontext.h> #include <asm/user.h> -extern void init_fpu(void); +extern void init_fpu(struct task_struct *); /* * FPU lazy state save handling... */
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This archive was generated by hypermail 2b29 : Tue Apr 23 2002 - 22:00:25 EST