source: bootcd/isolinux/syslinux-6.03/gpxe/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.
 */

FILE_LICENCE ( GPL2_OR_LATER );

#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 ( SHUTDOWN_BOOT );

        /* Jump to OS with flat physical addressing */
        DBGC ( image, "ELF %p starting execution at %lx\n", image, entry );
        __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,
};