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Date: Tue, 23 Aug 2005 21:36:40 -0400
From: Chuck Ebbert <76306.1226@compuserve.com>
Subject: Re: [patch 2.6.13-rc6] i386: fix incorrect FP signal delivery
To: Linus Torvalds <torvalds@osdl.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@osdl.org>,
       Ingo Molnar <mingo@elte.hu>,
       Marcelo Tosatti <marcelo.tosatti@cyclades.com>, Andi Kleen <ak@suse.de>
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On Tue, 23 Aug 2005 11:55:21 -0700 (PDT), Linus Torvalds wrote:

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

 I thought the extra code would be good documentation, but the comments
work just as well.  This is a little clearer (hand edited patch:)

--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -803,15 +803,17 @@ 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 Underflow
+			 * swd & 0x240 == 0x240: Stack Overflow
+			 * User must clear the SF bit (0x40) if set
+			 */
 			info.si_code = FPE_FLTINV;
-			/* Should we clear the SF or let user space do it ???? */
 			break;
 		case 0x002: /* Denormalize */
 		case 0x010: /* Underflow */
__
Chuck