i386/169730: [patch] libc/i386/gen/getcontextx.c::__getcontextx_size() is broken

[Dmitrij Tejblum]

>Number:         169730
>Category:       i386
>Synopsis:       [patch] libc/i386/gen/getcontextx.c::__getcontextx_size() is broken
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Jul 09 11:40:05 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Dmitrij Tejblum
>Release:        FreeBSD 9.0-STABLE
>Organization:
>Environment:
>Description:
__getcontextx_size() compute size of "extended" cpu state, depending on the CPU features. To do it, it should check if the bit CPUID2_OSXSAVE present in the "features2" field. But actually it checks some junk instead of the "features2" bitfield. 

To get features2 field, one should execure the "cpuid" instruction with EAX==1, but the code use EAX==0. See also the amd64 counterpart (libc/amd64/gen/getcontextx.c) for the correct (I believe) code.

>How-To-Repeat:

>Fix:


Patch attached with submission follows:

--- lib/libc/i386/gen/getcontextx.c.00	2012-02-22 01:18:59.000000000 +0400
+++ lib/libc/i386/gen/getcontextx.c	2012-07-06 21:45:04.000000000 +0400
@@ -64,15 +64,15 @@
 		if (cpuid_supported) {
 			__asm __volatile(
 			    "	pushl	%%ebx\n"
 			    "	cpuid\n"
 			    "	movl	%%ebx,%1\n"
 			    "	popl	%%ebx\n"
 			    : "=a" (p[0]), "=r" (p[1]), "=c" (p[2]), "=d" (p[3])
-			    :  "0" (0x0));
+			    :  "0" (1));
 			if ((p[2] & CPUID2_OSXSAVE) != 0) {
 				__asm __volatile(
 				    "	pushl	%%ebx\n"
 				    "	cpuid\n"
 				    "	movl	%%ebx,%1\n"
 				    "	popl	%%ebx\n"
 				    : "=a" (p[0]), "=r" (p[1]), "=c" (p[2]),


>Release-Note:
>Audit-Trail:
>Unformatted: