From: Michael Brown <mcb30@ipxe.org>
Date: Tue, 25 Oct 2011 14:48:20 +0000 (+0100)
Subject: [liba20] Preserve all non-segment registers when calling INT 15,2401
X-Git-Tag: v1.20.1~2062
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c77aece36a0085f1d7da6ca2b9f6c1234ddceb3b;p=thirdparty%2Fipxe.git

[liba20] Preserve all non-segment registers when calling INT 15,2401

Some BIOSes are reported to corrupt %ebx when using INT 15,2401 (see
http://opensolaris.org/jive/thread.jspa?messageID=377026).  Guard
against this by preserving all (non-segment) registers.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---

diff --git a/src/arch/i386/transitions/liba20.S b/src/arch/i386/transitions/liba20.S
index 594d62010..a60f1a546 100644
--- a/src/arch/i386/transitions/liba20.S
+++ b/src/arch/i386/transitions/liba20.S
@@ -96,8 +96,11 @@ test_a20_long:
 	.section ".text16.early", "awx", @progbits
 	.code16
 enable_a20_bios:
-	/* Preserve registers */
-	pushw	%ax
+
+	/* Preserve registers.  Be very paranoid, since some BIOSes
+	 * are reported to clobber %ebx
+	 */
+	pushal
 
 	/* Attempt INT 15,2401 */
 	movw	$0x2401, %ax
@@ -108,7 +111,7 @@ enable_a20_bios:
 	call	test_a20_short
 
 99:	/* Restore registers and return */
-	popw	%ax
+	popal
 	ret
 	.size	enable_a20_bios, . - enable_a20_bios