From 3715c8c721d312d79339a3b1b0b0900537c93b15 Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@gmail.com>
Date: Fri, 13 Jun 2008 10:26:49 +0100
Subject: [PATCH] [GDB] Zero-extend 16-bit segment registers

When the 16-bit segment registers are accessed using 32-bit instructions
the high order bytes are undefined on older CPUs.  We now explicitly
zero the high order bytes when snapshotting the CPU state.  This ensures
that the GDB stub reports consistent values for the segment registers.
---
 src/arch/i386/core/gdbidt.S | 18 ++++++++++++------
 src/tests/gdbstub_test.gdb  |  4 ++--
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/src/arch/i386/core/gdbidt.S b/src/arch/i386/core/gdbidt.S
index a4949232..860f7b01 100644
--- a/src/arch/i386/core/gdbidt.S
+++ b/src/arch/i386/core/gdbidt.S
@@ -163,12 +163,18 @@ int_page_fault:
 #define IH_OFFSET_FLUX_END ( IH_OFFSET_END - 20 )
 do_interrupt:
 	/* Store CPU state in GDB register snapshot */
-	pushl	%gs
-	pushl	%fs
-	pushl	%es
-	pushl	%ds
-	pushl	%ss
-	pushl	IH_OFFSET_FLUX_OLD_CS(%esp)
+	pushw	$0
+	pushw	%gs
+	pushw	$0
+	pushw	%fs
+	pushw	$0
+	pushw	%es
+	pushw	$0
+	pushw	%ds
+	pushw	$0
+	pushw	%ss
+	pushw	$0
+	pushw	IH_OFFSET_FLUX_OLD_CS + 2(%esp)
 	pushl	IH_OFFSET_FLUX_OLD_EFLAGS(%esp)
 	pushl	IH_OFFSET_FLUX_OLD_EIP(%esp)
 	pushl	%edi
diff --git a/src/tests/gdbstub_test.gdb b/src/tests/gdbstub_test.gdb
index 191799af..52aa693f 100755
--- a/src/tests/gdbstub_test.gdb
+++ b/src/tests/gdbstub_test.gdb
@@ -81,13 +81,13 @@ define gpxe_test_awatch
 	awatch watch_me
 
 	c
-	gpxe_assert $ecx 0x600d0000 "gpxe_test_awatch"
+	gpxe_assert $ecx 0x600d0000 "gpxe_test_awatch read"
 	if $ecx == 0x600d0000
 		c
 	end
 
 	c
-	gpxe_assert $ecx 0x600d0001 "gpxe_test_awatch"
+	gpxe_assert $ecx 0x600d0001 "gpxe_test_awatch write"
 	if $ecx == 0x600d0001
 		c
 	end