linux_load.c

open source bios with linux platform, very good and can be reused.

	if (*sep == '=') {
	    val = sep + 1;
	    len = end - val;
	} else {
	    val = 0;
	    len = 0;
	}

	/* Only initrd= and mem= are handled here. vga= is not,
	 * which I believe is a paramter to the realmode part of Linux,
	 * which we don't execute. */
	if (strcmp(name, "initrd") == 0) {
	    if (!val)
		printf("Missing filename to initrd parameter\n");
	    else {
		initrd = malloc(len + 1);
		memcpy(initrd, val, len);
		initrd[len] = 0;
		debug("initrd=%s\n", initrd);
	    }
	    /* Don't pass this to kernel */
	    to_kern = 0;
	} else if (strcmp(name, "mem") == 0) {
	    if (!val)
		printf("Missing value for mem parameter\n");
	    else {
		forced_memsize = strtoull_with_suffix(val, (char**)&val, 0);
		if (forced_memsize == 0)
		    printf("Invalid mem option, ignored\n");
		if (val != end) {
		    printf("Garbage after mem=<size>, ignored\n");
		    forced_memsize = 0;
		}
		debug("mem=%Lu\n", forced_memsize);
	    }
	    /* mem= is for both loader and kernel */
	    to_kern = 1;
	} else
	    to_kern = 1;

	if (to_kern) {
	    /* Copy to kernel command line buffer */
	    if (k_len != 0)
		kern_cmdline[k_len++] = ' '; /* put separator */
	    len = end - start;
	    if (k_len + len >= COMMAND_LINE_SIZE) {
		len = COMMAND_LINE_SIZE - k_len - 1;
		if (!toolong) {
		    printf("Kernel command line is too long; truncated to "
			    "%d bytes\n", COMMAND_LINE_SIZE-1);
		    toolong = 1;
		}
	    }
	    memcpy(kern_cmdline + k_len, start, len);
	    k_len += len;
	}

	start = end;
	while (*start == ' ')
	    start++;
    }
    kern_cmdline[k_len] = 0;
    debug("kernel command line (%d bytes): \"%s\"\n", k_len, kern_cmdline);

    return initrd;
}

/* Set command line location */
static void set_command_line_loc(struct linux_params *params,
	struct linux_header *hdr)
{
    if (hdr->protocol_version >= 0x202) {
	/* new style */
	params->cmd_line_ptr = COMMAND_LINE_LOC;
    } else {
	/* old style */
	params->cl_magic = CL_MAGIC_VALUE;
	params->cl_offset = COMMAND_LINE_LOC - LINUX_PARAM_LOC;
    }
}

/* Load 32-bit part of kernel */
static int load_linux_kernel(struct linux_header *hdr, uint32_t kern_addr)
{
    uint32_t kern_offset, kern_size;

    if (hdr->setup_sects == 0)
	hdr->setup_sects = 4;
    kern_offset = (hdr->setup_sects + 1) * 512;
    file_seek(kern_offset);
    kern_size = file_size() - kern_offset;
    debug("offset=%#x addr=%#x size=%#x\n", kern_offset, kern_addr, kern_size);

#if 0
    if (using_devsize) {
	printf("Attempt to load up to end of device as kernel; "
		"specify the image size\n");
	return 0;
    }
#endif

    printf("Loading kernel... ");
    if (lfile_read(phys_to_virt(kern_addr), kern_size) != kern_size) {
	printf("Can't read kernel\n");
	return 0;
    }
    printf("ok\n");

    return kern_size;
}

static int load_initrd(struct linux_header *hdr, struct sys_info *info,
	uint32_t kern_end, struct linux_params *params, const char *initrd_file)
{
    uint32_t max;
    uint32_t start, end, size;
    uint64_t forced;
    extern char _start[], _end[];

    if (!file_open(initrd_file)) {
	printf("Can't open initrd: %s\n", initrd_file);
	return -1;
    }

#if 0
    if (using_devsize) {
	printf("Attempt to load up to end of device as initrd; "
		"specify the image size\n");
	return -1;
    }
#endif

    size = file_size();


    /* Find out the kernel's restriction on how high the initrd can be
     * placed */
    if (hdr->protocol_version >= 0x203)
	max = hdr->initrd_addr_max;
    else
	max = 0x38000000; /* Hardcoded value for older kernels */
    
    /* FILO itself is at the top of RAM. (relocated)
     * So, try putting initrd just below us. */
    end = virt_to_phys(_start);
    if (end > max)
	end = max;

    /* If "mem=" option is given, we have to put the initrd within
     * the specified range. */
    if (forced_memsize) {
	forced = forced_memsize;
	if (forced > max)
	    forced = max;
	/* If the "mem=" is lower, it's easy */
	if (forced <= end)
	    end = forced;
	else {
	    /* Otherwise, see if we can put it above us */
	    if (virt_to_phys(_end) + size <= forced)
		end = forced; /* Ok */
	}
    }

    start = end - size;
    start &= ~0xfff; /* page align */
    end = start + size;

    debug("start=%#x end=%#x\n", start, end);

    if (start < kern_end) {
	printf("Initrd is too big to fit in memory\n");
	return -1;
    }

    printf("Loading initrd... ");
    if (lfile_read(phys_to_virt(start), size) != size) {
	printf("Can't read initrd\n");
	return -1;
    }
    printf("ok\n");

    params->initrd_start = start;
    params->initrd_size = size;

    return 0;
}

static void hardware_setup(void)
{
    /* Disable nmi */
    outb(0x80, 0x70);

    /* Make sure any coprocessor is properly reset.. */
    outb(0, 0xf0);
    outb(0, 0xf1);

    /* we're getting screwed again and again by this problem of the 8259. 
     * so we're going to leave this lying around for inclusion into 
     * crt0.S on an as-needed basis. 
     *
     * well, that went ok, I hope. Now we have to reprogram the interrupts :-(
     * we put them right after the intel-reserved hardware interrupts, at
     * int 0x20-0x2F. There they won't mess up anything. Sadly IBM really
     * messed this up with the original PC, and they haven't been able to
     * rectify it afterwards. Thus the bios puts interrupts at 0x08-0x0f,
     * which is used for the internal hardware interrupts as well. We just
     * have to reprogram the 8259's, and it isn't fun.
     */

    outb(0x11, 0x20);		/* initialization sequence to 8259A-1 */
    outb(0x11, 0xA0);		/* and to 8259A-2 */

    outb(0x20, 0x21);		/* start of hardware int's (0x20) */
    outb(0x28, 0xA1);		/* start of hardware int's 2 (0x28) */

    outb(0x04, 0x21);		/* 8259-1 is master */
    outb(0x02, 0xA1);		/* 8259-2 is slave */

    outb(0x01, 0x21);		/* 8086 mode for both */
    outb(0x01, 0xA1);

    outb(0xFF, 0xA1);		/* mask off all interrupts for now */
    outb(0xFB, 0x21);		/* mask all irq's but irq2 which is cascaded */
}

/* Start Linux */
static int start_linux(uint32_t kern_addr, struct linux_params *params)
{
    struct segment_desc *linux_gdt;
    struct context *ctx;
    //extern int cursor_x, cursor_y;

    ctx = init_context(phys_to_virt(STACK_LOC), 4096, 0);

    /* Linux expects GDT being in low memory */
    linux_gdt = phys_to_virt(GDT_LOC);
    memset(linux_gdt, 0, 13*sizeof(struct segment_desc));
    /* Normal kernel code/data segments */
    linux_gdt[2] = gdt[FLAT_CODE];
    linux_gdt[3] = gdt[FLAT_DATA];
    /* 2.6 kernel uses 12 and 13, but head.S uses backward-compatible
     * segments (2 and 3), so it SHOULD not be a problem. 
     * However, some distro kernels (eg. RH9) with backported threading 
     * patch use 12 and 13 also when booting... */
    linux_gdt[12] = gdt[FLAT_CODE];
    linux_gdt[13] = gdt[FLAT_DATA];
    ctx->gdt_base = GDT_LOC;
    ctx->gdt_limit = 14*8-1;
    ctx->cs = 0x10;
    ctx->ds = 0x18;
    ctx->es = 0x18;
    ctx->fs = 0x18;
    ctx->gs = 0x18;
    ctx->ss = 0x18;

    /* Parameter location */
    ctx->esi = virt_to_phys(params);

    /* Entry point */
    ctx->eip = kern_addr;

    debug("eip=%#x\n", kern_addr);
    printf("Jumping to entry point...\n");

#ifdef VGA_CONSOLE
    /* Update VGA cursor position.
     * This must be here because the printf changes the value! */
    params->orig_x = cursor_x;
    params->orig_y = cursor_y;
#endif
    
    /* Go... */
    ctx = switch_to(ctx);

    /* It's impossible but... */
    printf("Returned with eax=%#x\n", ctx->eax);

    return ctx->eax;
}

int linux_load(struct sys_info *info, const char *file, const char *cmdline)
{
    struct linux_header hdr;
    struct linux_params *params;
    uint32_t kern_addr, kern_size;
    char *initrd_file = 0;

    if (!file_open(file))
	return -1;

    kern_addr = load_linux_header(&hdr);
    if (kern_addr == 0)
	return LOADER_NOT_SUPPORT;

    params = phys_to_virt(LINUX_PARAM_LOC);
    init_linux_params(params, &hdr);
    set_memory_size(params, info);
    initrd_file = parse_command_line(cmdline, phys_to_virt(COMMAND_LINE_LOC));
    set_command_line_loc(params, &hdr);

    kern_size = load_linux_kernel(&hdr, kern_addr);
    if (kern_size == 0) {
	if (initrd_file)
	    free(initrd_file);
	return -1;
    }

    if (initrd_file) {
	if (load_initrd(&hdr, info, kern_addr+kern_size, params, initrd_file)
		!= 0) {
	    free(initrd_file);
	    return -1;
	}
	free(initrd_file);
    }

    hardware_setup();

    start_linux(kern_addr, params);
    return 0;
}