[ELF] Add ability to boot ELF images generated by wraplinux and mkelfImage

Delete ELF as a generic image type.  The method for invoking an
ELF-based image (as well as any tables that must be set up to allow it
to boot) will always depend on the specific architecture.  core/elf.c
now only provides the elf_load() function, to avoid duplicating
functionality between ELF-based image types.

Add arch/i386/image/elfboot.c, to handle the generic case of 32-bit
x86 ELF images.  We don't currently set up any multiboot tables, ELF
notes, etc.  This seems to be sufficient for loading kernels generated
using both wraplinux and coreboot's mkelfImage.

Note that while Etherboot 5.4 allowed ELF images to return, we don't.
There is no callback mechanism for the loaded image to shut down gPXE,
which means that we have to shut down before invoking the image.  This
means that we lose device state, protection against being trampled on,
etc.  It is not safe to continue afterwards.

src/arch/i386/image/elfboot.c

+/*
+ * Copyright (C) 2008 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <errno.h>
+#include <elf.h>
+#include <gpxe/image.h>
+#include <gpxe/elf.h>
+#include <gpxe/features.h>
+#include <gpxe/init.h>
+
+/**
+ * @file
+ *
+ * ELF bootable image
+ *
+ */
+
+FEATURE ( FEATURE_IMAGE, "ELF", DHCP_EB_FEATURE_ELF, 1 );
+
+struct image_type elfboot_image_type __image_type ( PROBE_NORMAL );
+
+/**
+ * Execute ELF image
+ *
+ * @v image		ELF image
+ * @ret rc		Return status code
+ */
+static int elfboot_exec ( struct image *image ) {
+	physaddr_t entry = image->priv.phys;
+
+	/* An ELF image has no callback interface, so we need to shut
+	 * down before invoking it.
+	 */
+	shutdown();
+
+	/* Jump to OS with flat physical addressing */
+	__asm__ __volatile__ ( PHYS_CODE ( "call *%%edi\n\t" )
+			       : : "D" ( entry )
+			       : "eax", "ebx", "ecx", "edx", "esi", "ebp",
+			         "memory" );
+
+	DBGC ( image, "ELF %p returned\n", image );
+
+	/* It isn't safe to continue after calling shutdown() */
+	while ( 1 ) {}
+
+	return -ECANCELED;  /* -EIMPOSSIBLE, anyone? */
+}
+
+/**
+ * Load ELF image into memory
+ *
+ * @v image		ELF file
+ * @ret rc		Return status code
+ */
+static int elfboot_load ( struct image *image ) {
+	Elf32_Ehdr ehdr;
+	static const uint8_t e_ident[] = {
+		[EI_MAG0]	= ELFMAG0,
+		[EI_MAG1]	= ELFMAG1,
+		[EI_MAG2]	= ELFMAG2,
+		[EI_MAG3]	= ELFMAG3,
+		[EI_CLASS]	= ELFCLASS32,
+		[EI_DATA]	= ELFDATA2LSB,
+		[EI_VERSION]	= EV_CURRENT,
+	};
+	int rc;
+
+	/* Read ELF header */
+	copy_from_user ( &ehdr, image->data, 0, sizeof ( ehdr ) );
+	if ( memcmp ( ehdr.e_ident, e_ident, sizeof ( e_ident ) ) != 0 ) {
+		DBG ( "Invalid ELF identifier\n" );
+		return -ENOEXEC;
+	}
+
+	/* This is an ELF image, valid or otherwise */
+	if ( ! image->type )
+		image->type = &elfboot_image_type;
+
+	/* Load the image using core ELF support */
+	if ( ( rc = elf_load ( image ) ) != 0 ) {
+		DBGC ( image, "ELF %p could not load: %s\n",
+		       image, strerror ( rc ) );
+		return rc;
+	}
+
+	return 0;
+}
+
+/** ELF image type */
+struct image_type elfboot_image_type __image_type ( PROBE_NORMAL ) = {
+	.name = "ELF",
+	.load = elfboot_load,
+	.exec = elfboot_exec,
+};

src/arch/i386/include/bits/errfile.h

 #define ERRFILE_multiboot      ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00030000 )
 #define ERRFILE_nbi	       ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00040000 )
 #define ERRFILE_pxe_image      ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00050000 )
+#define ERRFILE_elfboot	       ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00060000 )
 
 #define ERRFILE_undi		 ( ERRFILE_ARCH | ERRFILE_NET | 0x00000000 )
 #define ERRFILE_undiload	 ( ERRFILE_ARCH | ERRFILE_NET | 0x00010000 )

src/config.h

  *
  */
 #undef	IMAGE_NBI		/* NBI image support */
-#undef	IMAGE_ELF64		/* ELF64 image support */
-#undef	IMAGE_ELF		/* ELF image support */
+#define	IMAGE_ELF		/* ELF image support */
 #undef	IMAGE_FREEBSD		/* FreeBSD kernel image support */
 #define	IMAGE_MULTIBOOT		/* MultiBoot image support */
 #undef	IMAGE_AOUT		/* a.out image support */

src/core/config.c

 #ifdef IMAGE_NBI
 REQUIRE_OBJECT ( nbi );
 #endif
-#ifdef IMAGE_ELF64
-REQUIRE_OBJECT ( elf64 );
-#endif
 #ifdef IMAGE_ELF
-REQUIRE_OBJECT ( elf );
+REQUIRE_OBJECT ( elfboot );
 #endif
 #ifdef IMAGE_FREEBSD
 REQUIRE_OBJECT ( freebsd );

src/image/elf.c

  *
  * ELF image format
  *
+ * A "pure" ELF image is not a bootable image.  There are various
+ * bootable formats based upon ELF (e.g. Multiboot), which share
+ * common ELF-related functionality.
  */
 
 #include <errno.h>
 #include <gpxe/image.h>
 #include <gpxe/elf.h>
 
-struct image_type elf_image_type __image_type ( PROBE_NORMAL );
-
 typedef Elf32_Ehdr	Elf_Ehdr;
 typedef Elf32_Phdr	Elf_Phdr;
 typedef Elf32_Off	Elf_Off;
 
-/**
- * Execute ELF image
- *
- * @v image		ELF file
- * @ret rc		Return status code
- */
-static int elf_exec ( struct image *image __unused ) {
-	return -ENOTSUP;
-}
-
 /**
  * Load ELF segment into memory
  *
 	unsigned int phnum;
 	int rc;
 
+	/* Image type must already have been set by caller */
+	assert ( image->type != NULL );
+
 	/* Read ELF header */
 	copy_from_user ( &ehdr, image->data, 0, sizeof ( ehdr ) );
 	if ( memcmp ( &ehdr.e_ident[EI_MAG0], ELFMAG, SELFMAG ) != 0 ) {
 		return -ENOEXEC;
 	}
 
-	/* This is an ELF image, valid or otherwise */
-	if ( ! image->type )
-		image->type = &elf_image_type;
-
 	/* Read ELF program headers */
 	for ( phoff = ehdr.e_phoff , phnum = ehdr.e_phnum ; phnum ;
 	      phoff += ehdr.e_phentsize, phnum-- ) {
 
 	return 0;
 }
-
-/** ELF image type */
-struct image_type elf_image_type __image_type ( PROBE_NORMAL ) = {
-	.name = "ELF",
-	.load = elf_load,
-	.exec = elf_exec,
-};

src/include/gpxe/features.h

 #define DHCP_EB_FEATURE_MULTIBOOT	0x19 /**< Multiboot format */
 #define DHCP_EB_FEATURE_NBI		0x20 /**< NBI format */
 #define DHCP_EB_FEATURE_PXE		0x21 /**< PXE format */
+#define DHCP_EB_FEATURE_ELF		0x22 /**< ELF format */
 
 /** @} */