com32.c

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/*
 * Copyright (C) 2008 Daniel Verkamp <daniel@drv.nu>.
 *
 * 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
 *
 * SYSLINUX COM32 image format
 *
 */

FILE_LICENCE ( GPL2_OR_LATER );

#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <errno.h>
#include <assert.h>
#include <realmode.h>
#include <basemem.h>
#include <comboot.h>
#include <gpxe/uaccess.h>
#include <gpxe/image.h>
#include <gpxe/segment.h>
#include <gpxe/init.h>
#include <gpxe/memmap.h>

struct image_type com32_image_type __image_type ( PROBE_NORMAL );

/**
 * Execute COMBOOT image
 *
 * @v image             COM32 image
 * @ret rc              Return status code
 */
static int com32_exec ( struct image *image ) {
        struct memory_map memmap;
        unsigned int i;
        int state;
        uint32_t avail_mem_top;

        state = rmsetjmp ( comboot_return );

        switch ( state ) {
        case 0: /* First time through; invoke COM32 program */

                /* Get memory map */
                get_memmap ( &memmap );

                /* Find end of block covering COM32 image loading area */
                for ( i = 0, avail_mem_top = 0 ; i < memmap.count ; i++ ) {
                        if ( (memmap.regions[i].start <= COM32_START_PHYS) &&
                             (memmap.regions[i].end > COM32_START_PHYS + image->len) ) {
                                avail_mem_top = memmap.regions[i].end;
                                break;
                        }
                }

                DBGC ( image, "COM32 %p: available memory top = 0x%x\n",
                       image, avail_mem_top );

                assert ( avail_mem_top != 0 );

                com32_external_esp = phys_to_virt ( avail_mem_top );

                /* Hook COMBOOT API interrupts */
                hook_comboot_interrupts();

                /* Unregister image, so that a "boot" command doesn't
                 * throw us into an execution loop.  We never
                 * reregister ourselves; COMBOOT images expect to be
                 * removed on exit.
                 */
                unregister_image ( image );

                __asm__ __volatile__ (
                        "movl %%esp, (com32_internal_esp)\n\t" /* Save internal virtual address space ESP */
                        "movl (com32_external_esp), %%esp\n\t" /* Switch to COM32 ESP (top of available memory) */
                        "call _virt_to_phys\n\t"               /* Switch to flat physical address space */
                        "pushl %0\n\t"                         /* Pointer to CDECL helper function */
                        "pushl %1\n\t"                         /* Pointer to FAR call helper function */
                        "pushl %2\n\t"                         /* Size of low memory bounce buffer */
                        "pushl %3\n\t"                         /* Pointer to low memory bounce buffer */
                        "pushl %4\n\t"                         /* Pointer to INT call helper function */
                        "pushl %5\n\t"                         /* Pointer to the command line arguments */
                        "pushl $6\n\t"                         /* Number of additional arguments */
                        "call *%6\n\t"                         /* Execute image */
                        "call _phys_to_virt\n\t"               /* Switch back to internal virtual address space */
                        "movl (com32_internal_esp), %%esp\n\t" /* Switch back to internal stack */
                :
                :
                        /* %0 */ "r" ( virt_to_phys ( com32_cfarcall_wrapper ) ),
                        /* %1 */ "r" ( virt_to_phys ( com32_farcall_wrapper ) ),
                        /* %2 */ "r" ( get_fbms() * 1024 - (COM32_BOUNCE_SEG << 4) ),
                        /* %3 */ "i" ( COM32_BOUNCE_SEG << 4 ),
                        /* %4 */ "r" ( virt_to_phys ( com32_intcall_wrapper ) ),
                        /* %5 */ "r" ( virt_to_phys ( image->cmdline ) ),
                        /* %6 */ "r" ( COM32_START_PHYS )
                :
                        "memory" );
                DBGC ( image, "COM32 %p: returned\n", image );
                break;

        case COMBOOT_EXIT:
                DBGC ( image, "COM32 %p: exited\n", image );
                break;

        case COMBOOT_EXIT_RUN_KERNEL:
                DBGC ( image, "COM32 %p: exited to run kernel %p\n",
                       image, comboot_replacement_image );
                image->replacement = comboot_replacement_image;
                comboot_replacement_image = NULL;
                image_autoload ( image->replacement );
                break;

        case COMBOOT_EXIT_COMMAND:
                DBGC ( image, "COM32 %p: exited after executing command\n",
                       image );
                break;

        default:
                assert ( 0 );
                break;
        }

        unhook_comboot_interrupts();
        comboot_force_text_mode();

        return 0;
}

/**
 * Check image name extension
 * 
 * @v image             COM32 image
 * @ret rc              Return status code
 */
static int com32_identify ( struct image *image ) {
        const char *ext;
        static const uint8_t magic[] = { 0xB8, 0xFF, 0x4C, 0xCD, 0x21 };
        uint8_t buf[5];
        
        if ( image->len >= 5 ) {
                /* Check for magic number
                 * mov eax,21cd4cffh
                 * B8 FF 4C CD 21
                 */
                copy_from_user ( buf, image->data, 0, sizeof(buf) );
                if ( ! memcmp ( buf, magic, sizeof(buf) ) ) {
                        DBGC ( image, "COM32 %p: found magic number\n",
                               image );
                        return 0;
                }
        }

        /* Magic number not found; check filename extension */

        ext = strrchr( image->name, '.' );

        if ( ! ext ) {
                DBGC ( image, "COM32 %p: no extension\n",
                       image );
                return -ENOEXEC;
        }

        ++ext;

        if ( strcasecmp( ext, "c32" ) ) {
                DBGC ( image, "COM32 %p: unrecognized extension %s\n",
                       image, ext );
                return -ENOEXEC;
        }

        return 0;
}


/**
 * Load COM32 image into memory
 * @v image             COM32 image
 * @ret rc              Return status code
 */
static int comboot_load_image ( struct image *image ) {
        size_t filesz, memsz;
        userptr_t buffer;
        int rc;

        filesz = image->len;
        memsz = filesz;
        buffer = phys_to_user ( COM32_START_PHYS );
        if ( ( rc = prep_segment ( buffer, filesz, memsz ) ) != 0 ) {
                DBGC ( image, "COM32 %p: could not prepare segment: %s\n",
                       image, strerror ( rc ) );
                return rc;
        }

        /* Copy image to segment */
        memcpy_user ( buffer, 0, image->data, 0, filesz );

        return 0;
}

/**
 * Prepare COM32 low memory bounce buffer
 * @v image             COM32 image
 * @ret rc              Return status code
 */
static int comboot_prepare_bounce_buffer ( struct image * image ) {
        unsigned int seg;
        userptr_t seg_userptr;
        size_t filesz, memsz;
        int rc;

        seg = COM32_BOUNCE_SEG;
        seg_userptr = real_to_user ( seg, 0 );

        /* Ensure the entire 64k segment is free */
        memsz = 0xFFFF;
        filesz = 0;

        /* Prepare, verify, and load the real-mode segment */
        if ( ( rc = prep_segment ( seg_userptr, filesz, memsz ) ) != 0 ) {
                DBGC ( image, "COM32 %p: could not prepare bounce buffer segment: %s\n",
                       image, strerror ( rc ) );
                return rc;
        }

        return 0;
}

/**
 * Load COM32 image into memory
 *
 * @v image             COM32 image
 * @ret rc              Return status code
 */
static int com32_load ( struct image *image ) {
        int rc;

        DBGC ( image, "COM32 %p: name '%s', cmdline '%s'\n",
               image, image->name, image->cmdline );

        /* Check if this is a COMBOOT image */
        if ( ( rc = com32_identify ( image ) ) != 0 ) {
                return rc;
        }

        /* This is a COM32 image, valid or otherwise */
        if ( ! image->type )
                image->type = &com32_image_type;

        /* Load image */
        if ( ( rc = comboot_load_image ( image ) ) != 0 ) {
                return rc;
        }

        /* Prepare bounce buffer segment */
        if ( ( rc = comboot_prepare_bounce_buffer ( image ) ) != 0 ) {
                return rc;
        }

        return 0;
}

/** SYSLINUX COM32 image type */
struct image_type com32_image_type __image_type ( PROBE_NORMAL ) = {
        .name = "COM32",
        .load = com32_load,
        .exec = com32_exec,
};