[gPXE-devel] [PATCH] [comboot] Propagate carry flag from COMBOOT API

[Stefan Hajnoczi]

COMBOOT API calls set the carry flag on failure.  This was not being
propagated because the COMBOOT interrupt handler used iret to return
with EFLAGS restored from the stack.  This patch uses a far return that
discards the stale EFLAGS value from the stack instead.

Reported-by: Geoff Lywood <glywood at vmware.com>
Signed-off-by: Stefan Hajnoczi <stefanha at gmail.com>
---
This patch has been tested and reviewed in the issue tracker:
http://support.etherboot.org/index.php?do=details&task_id=77

 src/arch/i386/interface/syslinux/comboot_call.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/arch/i386/interface/syslinux/comboot_call.c b/src/arch/i386/interface/syslinux/comboot_call.c
index 51a1b6d..2ce39aa 100644
--- a/src/arch/i386/interface/syslinux/comboot_call.c
+++ b/src/arch/i386/interface/syslinux/comboot_call.c
@@ -669,7 +669,7 @@ void hook_comboot_interrupts ( ) {
 		              "pushw %%cs\n\t"
 		              "call prot_call\n\t"
 		              "addw $4, %%sp\n\t"
-		              "iret\n\t" )
+		              "lret $2\n\t" )
 		          : : "i" ( int20 ) );
 
 	hook_bios_interrupt ( 0x20, ( unsigned int ) int20_wrapper,
@@ -681,7 +681,7 @@ void hook_comboot_interrupts ( ) {
 		              "pushw %%cs\n\t"
 		              "call prot_call\n\t"
 		              "addw $4, %%sp\n\t"
-		              "iret\n\t" )
+		              "lret $2\n\t" )
 		          : : "i" ( int21 ) );
 
 	hook_bios_interrupt ( 0x21, ( unsigned int ) int21_wrapper,
@@ -693,8 +693,8 @@ void hook_comboot_interrupts ( ) {
 		              "pushw %%cs\n\t"
 		              "call prot_call\n\t"
 		              "addw $4, %%sp\n\t"
-		              "iret\n\t" )
-		          : : "i" ( int22) );
+		              "lret $2\n\t" )
+		          : : "i" ( int22 ) );
 
 	hook_bios_interrupt ( 0x22, ( unsigned int ) int22_wrapper,
 	                      &int22_vector );
-- 
1.7.0