Re: [patch 2.6.13-rc6] i386: fix incorrect FP signal delivery

[Linus Torvalds <torvalds@osdl.org>]

On Mon, 22 Aug 2005, Chuck Ebbert wrote:
>
> i386 floating-point exception handling has a bug that can cause error
> code 0 to be sent instead of the proper code during signal delivery.

Looking at your patch, I think it's too complicated.

The fact is, none of the "switch()" cases even _care_ about bits "0x240" 
from swd. The bug itself seems to be that we even look at it.

Wouldn't this simpler patch result in exactly the same behaviour?

		Linus
---
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
@@ -803,15 +803,14 @@ void math_error(void __user *eip)
 	 */
 	cwd = get_fpu_cwd(task);
 	swd = get_fpu_swd(task);
-	switch (((~cwd) & swd & 0x3f) | (swd & 0x240)) {
+	switch (swd & ~cwd & 0x3f) {
 		case 0x000:
 		default:
 			break;
 		case 0x001: /* Invalid Op */
-		case 0x041: /* Stack Fault */
-		case 0x241: /* Stack Fault | Direction */
+			/* swd & 0x240 == 0x040: Stack Fault */
+			/* swd & 0x240 == 0x240: Stack Fault | Direction */
 			info.si_code = FPE_FLTINV;
-			/* Should we clear the SF or let user space do it ???? */
 			break;
 		case 0x002: /* Denormalize */
 		case 0x010: /* Underflow */
-
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