[config] Make PXE stack a compile-time option

For extremely tight space requirements and specific applications, it is
sometimes desirable to create gPXE images that cannot provide the PXE API
functionality to client programs. Add a configuration header option,
PXE_STACK, that can be removed to remove this stack. Also add PXE_MENU
to control the PXE boot menu, which most uses of gPXE do not need.

Signed-off-by: Marty Connor <mdc@etherboot.org>

src/arch/i386/prefix/romprefix.S

@@ -126,6 +126,7 @@ prodstr_pci_id:
 	.size prodstr, . - prodstr
 
 	.globl	undiheader	
+	.weak	undiloader
 undiheader:
 	.ascii	"UNDI"			/* Signature */
 	.byte	undiheader_len		/* Length of structure */
@@ -495,6 +496,7 @@ init_message_done:
  *
  * May be either within option ROM space, or within PMM-allocated block.
  */
+	.globl	image_source
 image_source:
 	.long	0
 	.size	image_source, . - image_source
@@ -503,6 +505,7 @@ image_source:
  *
  * May be either at HIGHMEM_LOADPOINT, or within PMM-allocated block.
  */
+	.globl	decompress_to
 decompress_to:
 	.long	HIGHMEM_LOADPOINT
 	.size	decompress_to, . - decompress_to
@@ -644,50 +647,6 @@ exec_message:
 	.asciz	" starting execution\n"
 	.size exec_message, . - exec_message
 
-/* UNDI loader
- *
- * Called by an external program to load our PXE stack.
- */
-undiloader:
-	/* Save registers */
-	pushl	%esi
-	pushl	%edi
-	pushw	%ds
-	pushw	%es
-	pushw	%bx
-	/* ROM segment address to %ds */
-	pushw	%cs
-	popw	%ds
-	/* UNDI loader parameter structure address into %es:%di */
-	movw	%sp, %bx
-	movw	%ss:18(%bx), %di
-	movw	%ss:20(%bx), %es
-	/* Install to specified real-mode addresses */
-	pushw	%di
-	movw	%es:12(%di), %bx
-	movw	%es:14(%di), %ax
-	movl	image_source, %esi
-	movl	decompress_to, %edi
-	call	install_prealloc
-	popw	%di
-	/* Call UNDI loader C code */
-	pushl	$pxe_loader_call
-	pushw	%cs
-	pushw	$1f
-	pushw	%ax
-	pushw	$prot_call
-	lret
-1:	popw	%bx	/* discard */
-	popw	%bx	/* discard */
-	/* Restore registers and return */
-	popw	%bx
-	popw	%es
-	popw	%ds
-	popl	%edi
-	popl	%esi
-	lret
-	.size undiloader, . - undiloader
-
 /* Wait for key press specified by %bl (masked by %bh)
  *
  * Used by init and INT19 code when prompting user.  If the specified

src/arch/i386/prefix/undiloader.S

@@ -0,0 +1,49 @@
+	.text
+	.code16
+	.arch i386
+	.section ".prefix", "ax", @progbits
+
+/* UNDI loader
+ *
+ * Called by an external program to load our PXE stack.
+ */
+	.globl	undiloader
+undiloader:
+	/* Save registers */
+	pushl	%esi
+	pushl	%edi
+	pushw	%ds
+	pushw	%es
+	pushw	%bx
+	/* ROM segment address to %ds */
+	pushw	%cs
+	popw	%ds
+	/* UNDI loader parameter structure address into %es:%di */
+	movw	%sp, %bx
+	movw	%ss:18(%bx), %di
+	movw	%ss:20(%bx), %es
+	/* Install to specified real-mode addresses */
+	pushw	%di
+	movw	%es:12(%di), %bx
+	movw	%es:14(%di), %ax
+	movl	image_source, %esi
+	movl	decompress_to, %edi
+	call	install_prealloc
+	popw	%di
+	/* Call UNDI loader C code */
+	pushl	$pxe_loader_call
+	pushw	%cs
+	pushw	$1f
+	pushw	%ax
+	pushw	$prot_call
+	lret
+1:	popw	%bx	/* discard */
+	popw	%bx	/* discard */
+	/* Restore registers and return */
+	popw	%bx
+	popw	%es
+	popw	%ds
+	popl	%edi
+	popl	%esi
+	lret
+	.size undiloader, . - undiloader