[comboot] Propagate carry flag from COMBOOT API

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 propagates CF before
returning from the interrupt.

Reported-by: Geoff Lywood <glywood@vmware.com>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Marty Connor <mdc@etherboot.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/core/patch_cf.S

+/*
+ * Copyright (C) 2009 H. Peter Anvin <hpa@zytor.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER )
+
+	.text
+	.arch i386
+	.code16
+
+/****************************************************************************
+ * Set/clear CF on the stack as appropriate, assumes stack is as it should
+ * be immediately before IRET
+ ****************************************************************************
+ */
+	.section ".text16", "ax", @progbits
+	.globl patch_cf
+patch_cf:
+	pushw	%bp
+	movw	%sp, %bp
+	setc	8(%bp)	/* Set/reset CF; clears PF, AF, ZF, SF */
+	popw	%bp
+	ret
+	.size patch_cf, . - patch_cf

src/arch/i386/firmware/pcbios/e820mangler.S

 	ret
 	.size get_mangled_e820, . - get_mangled_e820
 
-/****************************************************************************
- * Set/clear CF on the stack as appropriate, assumes stack is as it should
- * be immediately before IRET
- ****************************************************************************
- */
-patch_cf:
-	pushw	%bp
-	movw	%sp, %bp
-	setc	8(%bp)	/* Set/reset CF; clears PF, AF, ZF, SF */
-	popw	%bp
-	ret
-
 /****************************************************************************
  * INT 15,e820 handler
  ****************************************************************************

src/arch/i386/interface/syslinux/comboot_call.c

 		              "pushw %%cs\n\t"
 		              "call prot_call\n\t"
 		              "addw $4, %%sp\n\t"
+			      "call patch_cf\n\t"
 		              "iret\n\t" )
 		          : : "i" ( int20 ) );
 
 		              "pushw %%cs\n\t"
 		              "call prot_call\n\t"
 		              "addw $4, %%sp\n\t"
+			      "call patch_cf\n\t"
 		              "iret\n\t" )
 		          : : "i" ( int21 ) );
 
 		              "pushw %%cs\n\t"
 		              "call prot_call\n\t"
 		              "addw $4, %%sp\n\t"
+			      "call patch_cf\n\t"
 		              "iret\n\t" )
 		          : : "i" ( int22) );