Re: FPU-intensive programs crashing with floating point exception on Cyrix MII

[Linus Torvalds <torvalds@osdl.org>]

On Sun, 21 Aug 2005, Chuck Ebbert wrote:
>
> > MATH ERROR: cwd = 0x37f, swd = 0x2800     <===========
> 
>  The error I marked has no exception flags set.  The rest are all (masked)
> denormal exceptions.  Why your Cyrix MII would cause an FPU exception in these
> cases is beyond me.  Could you try the statically-linked mprime program?

Also, please try this one, to see where it happens.

			Linus

---
diff --git a/arch/i386/kernel/i8259.c b/arch/i386/kernel/i8259.c
--- a/arch/i386/kernel/i8259.c
+++ b/arch/i386/kernel/i8259.c
@@ -357,11 +357,11 @@ void init_8259A(int auto_eoi)
 
 static irqreturn_t math_error_irq(int cpl, void *dev_id, struct pt_regs *regs)
 {
-	extern void math_error(void __user *);
+	extern void math_error(struct pt_regs *);
 	outb(0,0xF0);
 	if (ignore_fpu_irq || !boot_cpu_data.hard_math)
 		return IRQ_NONE;
-	math_error((void __user *)regs->eip);
+	math_error(regs);
 	return IRQ_HANDLED;
 }
 
diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -774,8 +774,9 @@ clear_TF_reenable:
  * the correct behaviour even in the presence of the asynchronous
  * IRQ13 behaviour
  */
-void math_error(void __user *eip)
+void math_error(struct pt_regs *regs)
 {
+	void __user *eip = (void __user *)regs->eip;
 	struct task_struct * task;
 	siginfo_t info;
 	unsigned short cwd, swd;
@@ -805,6 +806,7 @@ void math_error(void __user *eip)
 	swd = get_fpu_swd(task);
 	switch (((~cwd) & swd & 0x3f) | (swd & 0x240)) {
 		case 0x000:
+			show_regs(regs);
 		default:
 			break;
 		case 0x001: /* Invalid Op */
@@ -833,7 +835,7 @@ void math_error(void __user *eip)
 fastcall void do_coprocessor_error(struct pt_regs * regs, long error_code)
 {
 	ignore_fpu_irq = 1;
-	math_error((void __user *)regs->eip);
+	math_error(regs);
 }
 
 static void simd_math_error(void __user *eip)
-
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