Applied a modified version of holger's regparm patches.

src/arch/i386/Config

 # this is almost always a win. the kernel uses it, too.
 CFLAGS+= -mpreferred-stack-boundary=2
 
+# use regparm for all functions - C functions called from assembly (or
+# vice versa) need __cdecl now
+CFLAGS+= -mregparm=3
+
+# use -mrtd (same __cdecl requirements as above)
+CFLAGS+= -mrtd
+
+# this is the logical complement to -mregparm=3. 
+# it doesn't currently buy us anything, but if anything ever tries
+# to return small structures, let's be prepared
+CFLAGS+= -freg-struct-return
+
 LDFLAGS+=	-N --no-check-sections
 
 ifeq "$(shell uname -s)" "FreeBSD"

src/arch/i386/core/relocate.c

  * address space, and returns the physical address of the new location
  * to the prefix in %edi.
  */
-void relocate ( struct i386_all_regs *ix86 ) {
+__cdecl void relocate ( struct i386_all_regs *ix86 ) {
 	struct memory_map memmap;
 	unsigned long start, end, size, padded_size;
 	unsigned long new_start, new_end;

src/arch/i386/interface/pcbios/int13.c

  * INT 13 handler
  *
  */
-static void int13 ( struct i386_all_regs *ix86 ) {
+static __cdecl void int13 ( struct i386_all_regs *ix86 ) {
 	int command = ix86->regs.ah;
 	unsigned int bios_drive = ix86->regs.dl;
 	unsigned int original_bios_drive = bios_drive;

src/arch/i386/interface/pxe/pxe_call.c

  * @v es:di		Address of PXE parameter block
  * @ret ax		PXE exit code
  */
-void pxe_api_call ( struct i386_all_regs *ix86 ) {
+__cdecl void pxe_api_call ( struct i386_all_regs *ix86 ) {
 	int opcode = ix86->regs.bx;
 	userptr_t parameters = real_to_user ( ix86->segs.es, ix86->regs.di );
 	size_t param_len;
  * @v es:di		Address of PXE parameter block
  * @ret ax		PXE exit code
  */
-void pxe_loader_call ( struct i386_all_regs *ix86 ) {
+__cdecl void pxe_loader_call ( struct i386_all_regs *ix86 ) {
 	userptr_t uparams = real_to_user ( ix86->segs.es, ix86->regs.di );
 	struct s_UNDI_LOADER params;
 	PXENV_EXIT_t ret;

src/core/main.c

  *
  * @ret rc		Return status code
  */
-int main ( void ) {
+__cdecl int main ( void ) {
 
 	initialise();
 	startup();

src/include/compiler.h

 /** Declare a variable or data structure as unused. */
 #define __unused __attribute__ (( unused ))
 
+/** Apply standard C calling conventions */
+#define __cdecl __attribute__ (( cdecl , regparm(0) ))
+
 /**
  * Declare a function as used.
  *