xref: /external/syslinux/gpxe/src/arch/i386/image/comboot.c

/*
 * 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 COMBOOT (16-bit) 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/features.h>

FEATURE ( FEATURE_IMAGE, "COMBOOT", DHCP_EB_FEATURE_COMBOOT, 1 );

struct image_type comboot_image_type __image_type ( PROBE_NORMAL );

/**
 * COMBOOT PSP, copied to offset 0 of code segment
 */
struct comboot_psp {
	/** INT 20 instruction, executed if COMBOOT image returns with RET */
	uint16_t int20;
	/** Segment of first non-free paragraph of memory */
	uint16_t first_non_free_para;
};

/** Offset in PSP of command line */
#define COMBOOT_PSP_CMDLINE_OFFSET 0x81

/** Maximum length of command line in PSP
 * (127 bytes minus space and CR) */
#define COMBOOT_MAX_CMDLINE_LEN    125


/**
 * Copy command line to PSP
 *
 * @v image		COMBOOT image
 */
static void comboot_copy_cmdline ( struct image * image, userptr_t seg_userptr ) {
	const char *cmdline = ( image->cmdline ? image->cmdline : "" );
	int cmdline_len = strlen ( cmdline );
	if( cmdline_len > COMBOOT_MAX_CMDLINE_LEN )
		cmdline_len = COMBOOT_MAX_CMDLINE_LEN;
	uint8_t len_byte = cmdline_len;
	char spc = ' ', cr = '\r';

	/* Copy length to byte before command line */
	copy_to_user ( seg_userptr, COMBOOT_PSP_CMDLINE_OFFSET - 1,
	               &len_byte, 1 );

	/* Command line starts with space */
	copy_to_user ( seg_userptr,
	               COMBOOT_PSP_CMDLINE_OFFSET,
	               &spc, 1 );

	/* Copy command line */
	copy_to_user ( seg_userptr,
	               COMBOOT_PSP_CMDLINE_OFFSET + 1,
	               cmdline, cmdline_len );

	/* Command line ends with CR */
	copy_to_user ( seg_userptr,
	               COMBOOT_PSP_CMDLINE_OFFSET + cmdline_len + 1,
	               &cr, 1 );
}

/**
 * Initialize PSP
 *
 * @v image		COMBOOT image
 * @v seg_userptr	segment to initialize
 */
static void comboot_init_psp ( struct image * image, userptr_t seg_userptr ) {
	struct comboot_psp psp;

	/* Fill PSP */

	/* INT 20h instruction, byte order reversed */
	psp.int20 = 0x20CD;

	/* get_fbms() returns BIOS free base memory counter, which is in
	 * kilobytes; x * 1024 / 16 == x * 64 == x << 6 */
	psp.first_non_free_para = get_fbms() << 6;

	DBGC ( image, "COMBOOT %p: first non-free paragraph = 0x%x\n",
	       image, psp.first_non_free_para );

	/* Copy the PSP to offset 0 of segment.
	 * The rest of the PSP was already zeroed by
	 * comboot_prepare_segment. */
	copy_to_user ( seg_userptr, 0, &psp, sizeof( psp ) );

	/* Copy the command line to the PSP */
	comboot_copy_cmdline ( image, seg_userptr );
}

/**
 * Execute COMBOOT image
 *
 * @v image		COMBOOT image
 * @ret rc		Return status code
 */
static int comboot_exec ( struct image *image ) {
	userptr_t seg_userptr = real_to_user ( COMBOOT_PSP_SEG, 0 );
	int state;

	state = rmsetjmp ( comboot_return );

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

		/* Initialize PSP */
		comboot_init_psp ( image, seg_userptr );

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

		DBGC ( image, "executing 16-bit COMBOOT image at %4x:0100\n",
		       COMBOOT_PSP_SEG );

		/* 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 );

		/* Store stack segment at 0x38 and stack pointer at 0x3A
		 * in the PSP and jump to the image */
		__asm__ __volatile__ (
		    REAL_CODE ( /* Save return address with segment on old stack */
				    "popw %%ax\n\t"
				    "pushw %%cs\n\t"
				    "pushw %%ax\n\t"
				    /* Set DS=ES=segment with image */
				    "movw %w0, %%ds\n\t"
				    "movw %w0, %%es\n\t"
				    /* Set SS:SP to new stack (end of image segment) */
				    "movw %w0, %%ss\n\t"
				    "xor %%sp, %%sp\n\t"
				    "pushw $0\n\t"
				    "pushw %w0\n\t"
				    "pushw $0x100\n\t"
				    /* Zero registers (some COM files assume GP regs are 0) */
				    "xorw %%ax, %%ax\n\t"
				    "xorw %%bx, %%bx\n\t"
				    "xorw %%cx, %%cx\n\t"
				    "xorw %%dx, %%dx\n\t"
				    "xorw %%si, %%si\n\t"
				    "xorw %%di, %%di\n\t"
				    "xorw %%bp, %%bp\n\t"
				    "lret\n\t" )
					 : : "r" ( COMBOOT_PSP_SEG ) : "eax" );
		DBGC ( image, "COMBOOT %p: returned\n", image );
		break;

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

	case COMBOOT_EXIT_RUN_KERNEL:
		DBGC ( image, "COMBOOT %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, "COMBOOT %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		COMBOOT image
 * @ret rc		Return status code
 */
static int comboot_identify ( struct image *image ) {
	const char *ext;

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

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

	++ext;

	if ( strcasecmp( ext, "com" ) && strcasecmp( ext, "cbt" ) ) {
		DBGC ( image, "COMBOOT %p: unrecognized extension %s\n",
		       image, ext );
		return -ENOEXEC;
	}

	return 0;
}

/**
 * Load COMBOOT image into memory, preparing a segment and returning it
 * @v image		COMBOOT image
 * @ret rc		Return status code
 */
static int comboot_prepare_segment ( struct image *image )
{
	userptr_t seg_userptr;
	size_t filesz, memsz;
	int rc;

	/* Load image in segment */
	seg_userptr = real_to_user ( COMBOOT_PSP_SEG, 0 );

	/* Allow etra 0x100 bytes before image for PSP */
	filesz = image->len + 0x100;

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

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

	/* Zero PSP */
	memset_user ( seg_userptr, 0, 0, 0x100 );

	/* Copy image to segment:0100 */
	memcpy_user ( seg_userptr, 0x100, image->data, 0, image->len );

	return 0;
}

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

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

	/* Check if this is a COMBOOT image */
	if ( ( rc = comboot_identify ( image ) ) != 0 ) {

		return rc;
	}

	/* This is a 16-bit COMBOOT image, valid or otherwise */
	if ( ! image->type )
		image->type = &comboot_image_type;

	/* Sanity check for filesize */
	if( image->len >= 0xFF00 ) {
		DBGC( image, "COMBOOT %p: image too large\n",
		      image );
		return -ENOEXEC;
	}

	/* Prepare segment and load image */
	if ( ( rc = comboot_prepare_segment ( image ) ) != 0 ) {
		return rc;
	}

	return 0;
}

/** SYSLINUX COMBOOT (16-bit) image type */
struct image_type comboot_image_type __image_type ( PROBE_NORMAL ) = {
	.name = "COMBOOT",
	.load = comboot_load,
	.exec = comboot_exec,
};