[pxe] Set %ax to zero on entry to PXE NBP

This is not strictly an entry requirement, but it does mean that a PXE
NBP returning without setting %ax will appear to have returned
success.

diff --git a/src/arch/i386/interface/pxe/pxe_call.c b/src/arch/i386/interface/pxe/pxe_call.c
index 320ae12..06dee25 100644 (file)
--- a/src/arch/i386/interface/pxe/pxe_call.c
+++ b/src/arch/i386/interface/pxe/pxe_call.c
@@ -433,23 +433,24 @@ void pxe_init_structures ( void ) {
  * @ret rc             Return status code
  */
 int pxe_start_nbp ( void ) {
-       int discard_b, discard_c, discard_d;
+       int discard_b, discard_c, discard_d, discard_D;
        uint16_t rc;
 
        /* Far call to PXE NBP */
-       __asm__ __volatile__ ( REAL_CODE ( "pushw %%cx\n\t"
-                                          "pushw %%ax\n\t"
-                                          "movw %%cx, %%es\n\t"
+       __asm__ __volatile__ ( REAL_CODE ( "movw %%cx, %%es\n\t"
+                                          "pushw %%es\n\t"
+                                          "pushw %%di\n\t"
                                           "sti\n\t"
                                           "lcall $0, $0x7c00\n\t"
                                           "addw $4, %%sp\n\t" )
                               : "=a" ( rc ), "=b" ( discard_b ),
-                                "=c" ( discard_c ), "=d" ( discard_d )
-                              : "a" ( __from_text16 ( &ppxe ) ),
-                                "b" ( __from_text16 ( &pxenv ) ),
+                                "=c" ( discard_c ), "=d" ( discard_d ),
+                                "=D" ( discard_D )
+                              : "a" ( 0 ), "b" ( __from_text16 ( &pxenv ) ),
                                 "c" ( rm_cs ),
-                                "d" ( virt_to_phys ( &pxenv ) )
-                              : "esi", "edi", "ebp", "memory" );
+                                "d" ( virt_to_phys ( &pxenv ) ),
+                                "D" ( __from_text16 ( &ppxe ) )
+                              : "esi", "ebp", "memory" );
 
        return rc;
 }