[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/include/pxe_call.h

 extern int pxe_deactivate ( void );
 extern int pxe_start_nbp ( void );
 extern __asmcall void pxe_api_call ( struct i386_all_regs *ix86 );
+extern int _pxe_api_call_weak ( struct i386_all_regs *ix86 )
+	__attribute__ (( weak ));
+
+/**
+ * Dispatch PXE API call weakly
+ *
+ * @v ix86		Registers for PXE call
+ * @ret present		Zero if the PXE stack is present, nonzero if not
+ *
+ * A successful return only indicates that the PXE stack was available
+ * for dispatching the call; it says nothing about the success of
+ * whatever the call asked for.
+ */
+static inline int pxe_api_call_weak ( struct i386_all_regs *ix86 )
+{
+	if ( _pxe_api_call_weak != NULL )
+		return _pxe_api_call_weak ( ix86 );
+	return -1;
+}
 
 #endif /* _PXE_CALL_H */

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

 	ix86->regs.ax = ret;
 }
 
+/**
+ * Dispatch weak PXE API call with PXE stack available
+ *
+ * @v ix86		Registers for PXE call
+ * @ret present		Zero (PXE stack present)
+ */
+int _pxe_api_call_weak ( struct i386_all_regs *ix86 )
+{
+	pxe_api_call ( ix86 );
+	return 0;
+}
+
 /**
  * Dispatch PXE loader call
  *

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

 		break;
 
 	case 0x0009: /* Call PXE Stack */
-		pxe_api_call ( ix86 );
-		ix86->flags &= ~CF;
+		if ( pxe_api_call_weak ( ix86 ) != 0 )
+			ix86->flags |= CF;
+		else
+			ix86->flags &= ~CF;
 		break;
 
 	case 0x000A: /* Get Derivative-Specific Information */

src/arch/i386/prefix/romprefix.S

 	.size prodstr, . - prodstr
 
 	.globl	undiheader	
+	.weak	undiloader
 undiheader:
 	.ascii	"UNDI"			/* Signature */
 	.byte	undiheader_len		/* Length of structure */
  *
  * May be either within option ROM space, or within PMM-allocated block.
  */
+	.globl	image_source
 image_source:
 	.long	0
 	.size	image_source, . - 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
 	.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

+	.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

src/config/config.c

 REQUIRE_OBJECT ( ipv4 );
 #endif
 
+/*
+ * Drag in all requested PXE support
+ *
+ */
+#ifdef PXE_MENU
+REQUIRE_OBJECT ( pxemenu );
+#endif
+#ifdef PXE_STACK
+REQUIRE_OBJECT ( pxe_call );
+#endif
+
 /*
  * Drag in all requested download protocols
  *

src/config/config_romprefix.c

+/*
+ * 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, or (at
+ * your option) any later version.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <config/general.h>
+
+/** @file
+ *
+ * ROM prefix configuration options
+ *
+ */
+
+/*
+ * Provide UNDI loader if PXE stack is requested
+ *
+ */
+#ifdef PXE_STACK
+REQUIRE_OBJECT ( undiloader );
+#endif

src/config/defaults/pcbios.h

 #define IMAGE_BZIMAGE		/* Linux bzImage image support */
 #define IMAGE_COMBOOT		/* SYSLINUX COMBOOT image support */
 
+#define PXE_STACK		/* PXE stack in gPXE - required for PXELINUX */
+#define PXE_MENU		/* PXE menu booting */
 #define	PXE_CMD			/* PXE commands */
 
 #define	SANBOOT_PROTO_ISCSI	/* iSCSI protocol */

src/config/general.h

 
 #define	NET_PROTO_IPV4		/* IPv4 protocol */
 
+/*
+ * PXE support
+ *
+ */
+//#undef	PXE_STACK		/* PXE stack in gPXE - you want this! */
+//#undef	PXE_MENU		/* PXE menu booting */
+
 /*
  * Download protocols
  *

src/include/usr/autoboot.h

 extern int boot_next_server_and_filename ( struct in_addr next_server,
 					   const char *filename );
 extern int boot_root_path ( const char *root_path );
-extern int pxe_menu_boot ( struct net_device *netdev );
+
+extern int pxe_menu_boot ( struct net_device *netdev )
+	__attribute__ (( weak ));
 
 #endif /* _USR_AUTOBOOT_H */

src/usr/autoboot.c

 			       buf, sizeof ( buf ) );
 	pxe_discovery_control =
 		fetch_uintz_setting ( NULL, &pxe_discovery_control_setting );
-	if ( ( strcmp ( buf, "PXEClient" ) == 0 ) &&
+	if ( ( strcmp ( buf, "PXEClient" ) == 0 ) && pxe_menu_boot != NULL &&
 	     setting_exists ( NULL, &pxe_boot_menu_setting ) &&
 	     ( ! ( ( pxe_discovery_control & PXEBS_SKIP ) &&
 		   setting_exists ( NULL, &filename_setting ) ) ) ) {