Use fixed-width fields in struct undi_device, so that pxeprefix.S will be

able to populate the structure.

src/arch/i386/drivers/net/undiload.c

 	/* Debug info */
 	DBGC ( undi, "UNDI %p loading UNDI ROM %p to CS %04x DS %04x for ",
 	       undi, undirom, undi_loader.UNDI_CS, undi_loader.UNDI_DS );
-	if ( undi->pci_busdevfn ) {
+	if ( undi->pci_busdevfn != 0xffff ) {
 		unsigned int bus = ( undi->pci_busdevfn >> 8 );
 		unsigned int devfn = ( undi->pci_busdevfn & 0xff );
 		DBGC ( undi, "PCI %02x:%02x.%x\n",
 		       bus, PCI_SLOT ( devfn ), PCI_FUNC ( devfn ) );
 	}
-	if ( undi->isapnp_csn != -1U ) {
+	if ( undi->isapnp_csn != 0xffff ) {
 		DBGC ( undi, "ISAPnP(%04x) CSN %04x\n",
 		       undi->isapnp_read_port, undi->isapnp_csn );
 	}
 int undi_load_pci ( struct undi_device *undi, struct undi_rom *undirom,
 		    unsigned int bus, unsigned int devfn ) {
 	undi->pci_busdevfn = ( ( bus << 8 ) | devfn );
-	undi->isapnp_csn = -1U;
-	undi->isapnp_read_port = -1U;
+	undi->isapnp_csn = 0xffff;
+	undi->isapnp_read_port = 0xffff;
 	return undi_load ( undi, undirom );
 }
 

src/arch/i386/include/undi.h

 #include <gpxe/device.h>
 #include <pxe_types.h>
 
-/** An UNDI device */
+/** An UNDI device
+ *
+ * This structure is used by assembly code as well as C; do not alter
+ * this structure without editing pxeprefix.S to match.
+ */
 struct undi_device {
+	/** PXENV+ structure address */
+	SEGOFF16_t pxenv;
+	/** !PXE structure address */
+	SEGOFF16_t ppxe;
+	/** Entry point */
+	SEGOFF16_t entry;
+	/** Free base memory after load */
+	UINT16_t fbms;
+	/** Free base memory prior to load */
+	UINT16_t restore_fbms;
+	/** PCI bus:dev.fn, or 0xffff */
+	UINT16_t pci_busdevfn;
+	/** ISAPnP card select number, or 0xffff */
+	UINT16_t isapnp_csn;
+	/** ISAPnP read port, or 0xffff */
+	UINT16_t isapnp_read_port;
+	/** Padding */
+	UINT16_t pad;
+
 	/** Generic device */
 	struct device dev;
 	/** Driver-private data
 	 * field.
 	 */
 	void *priv;
-
-	/** PXENV+ structure address */
-	SEGOFF16_t pxenv;
-	/** !PXE structure address */
-	SEGOFF16_t ppxe;
-	/** Entry point */
-	SEGOFF16_t entry;
-	/** PCI bus:dev.fn, or 0 */
-	unsigned int pci_busdevfn;
-	/** ISAPnP card select number, or -1U */
-	unsigned int isapnp_csn;
-	/** ISAPnP read port, or -1U */
-	unsigned int isapnp_read_port;
-	/** Free base memory prior to load */
-	unsigned int restore_fbms;
-	/** Free base memory after load */
-	unsigned int fbms;
-};
+} __attribute__ (( packed ));
 
 /**
  * Set UNDI driver-private data