multiboot.c File Reference

Multiboot image format. More...

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include <realmode.h>
#include <multiboot.h>
#include <ipxe/image.h>
#include <ipxe/segment.h>
#include <ipxe/memmap.h>
#include <ipxe/elf.h>
#include <ipxe/init.h>
#include <ipxe/features.h>
#include <ipxe/uri.h>
#include <ipxe/version.h>

Go to the source code of this file.

Macros
#define	MAX_MODULES   8
	Maximum number of modules we will allow for.
#define	MAX_MEMMAP   8
	Maximum number of memory map entries.
#define	MB_MAX_CMDLINE   512
	Maximum combined length of command lines.
#define	MB_SUPPORTED_FLAGS
	Multiboot flags that we support.
#define	MB_COMPULSORY_FLAGS   0x0000ffff
	Compulsory feature multiboot flags.
#define	MB_OPTIONAL_FLAGS   0xffff0000
	Optional feature multiboot flags.
#define	MB_UNSUPPORTED_FLAGS   ( MB_COMPULSORY_FLAGS & ~MB_SUPPORTED_FLAGS )
	Multiboot flags that we don't support.
#define	mb_cmdlines   __use_data16 ( mb_cmdlines )
#define	mbinfo   __use_data16 ( mbinfo )
#define	mb_bootloader_name   __use_data16 ( mb_bootloader_name )
#define	mbmemmap   __use_data16 ( mbmemmap )
#define	mbmodules   __use_data16 ( mbmodules )

Functions
	FILE_LICENCE (GPL2_OR_LATER_OR_UBDL)
	FEATURE (FEATURE_IMAGE, "MBOOT", DHCP_EB_FEATURE_MULTIBOOT, 1)
static char	__bss16_array (mb_cmdlines, [MB_MAX_CMDLINE])
	Multiboot module command lines.
static void	multiboot_build_memmap (struct image *image, struct multiboot_info *mbinfo, struct multiboot_memory_map *mbmemmap, unsigned int limit)
	Build multiboot memory map.
static physaddr_t	multiboot_add_cmdline (struct image *image)
	Add command line in base memory.
static int	multiboot_add_modules (struct image *image, physaddr_t start, struct multiboot_info *mbinfo, struct multiboot_module *modules, unsigned int limit)
	Add multiboot modules.
static struct multiboot_info	__bss16 (mbinfo)
	The multiboot information structure.
static char	__bss16_array (mb_bootloader_name, [32])
	The multiboot bootloader name.
static struct multiboot_memory_map	__bss16_array (mbmemmap, [MAX_MEMMAP])
	The multiboot memory map.
static struct multiboot_module	__bss16_array (mbmodules, [MAX_MODULES])
	The multiboot module list.
static int	multiboot_find_header (struct image *image)
	Find multiboot header.
static int	multiboot_load_raw (struct image *image, size_t offset, physaddr_t *entry, physaddr_t *max)
	Load raw multiboot image into memory.
static int	multiboot_load_elf (struct image *image, physaddr_t *entry, physaddr_t *max)
	Load ELF multiboot image into memory.
static int	multiboot_exec (struct image *image)
	Execute multiboot image.
static int	multiboot_probe (struct image *image)
	Probe multiboot image.
struct image_type multiboot_image_type	__image_type (PROBE_MULTIBOOT)
	Multiboot image type.

Variables
static unsigned int	mb_cmdline_offset
	Offset within module command lines.

Detailed Description

Multiboot image format.

Definition in file multiboot.c.

Macro Definition Documentation

MAX_MODULES

#define MAX_MODULES   8

Maximum number of modules we will allow for.

If this has bitten you: sorry. I did have a perfect scheme with a dynamically allocated list of modules on the protected-mode stack, but it was incompatible with some broken OSes that can only access low memory at boot time (even though we kindly set up 4GB flat physical addressing as per the multiboot specification.

Definition at line 60 of file multiboot.c.

Referenced by __bss16_array().

MAX_MEMMAP

#define MAX_MEMMAP   8

Maximum number of memory map entries.

Definition at line 63 of file multiboot.c.

Referenced by __bss16_array().

MB_MAX_CMDLINE

#define MB_MAX_CMDLINE   512

Maximum combined length of command lines.

Again; sorry. Some broken OSes zero out any non-base memory that isn't part of the loaded module set, so we can't just use virt_to_phys(cmdline) to point to the command lines, even though this would comply with the Multiboot spec.

Definition at line 73 of file multiboot.c.

Referenced by __bss16_array().

MB_SUPPORTED_FLAGS

#define MB_SUPPORTED_FLAGS

Value:

                             ( MB_FLAG_PGALIGN | MB_FLAG_MEMMAP | \
                             MB_FLAG_VIDMODE | MB_FLAG_RAW )

Multiboot flags that we support.

Definition at line 76 of file multiboot.c.

#define MB_SUPPORTED_FLAGS ( MB_FLAG_PGALIGN | MB_FLAG_MEMMAP | \
                             MB_FLAG_VIDMODE | MB_FLAG_RAW )

MB_COMPULSORY_FLAGS

#define MB_COMPULSORY_FLAGS   0x0000ffff

Compulsory feature multiboot flags.

Definition at line 80 of file multiboot.c.

MB_OPTIONAL_FLAGS

#define MB_OPTIONAL_FLAGS   0xffff0000

Optional feature multiboot flags.

Definition at line 83 of file multiboot.c.

MB_UNSUPPORTED_FLAGS

#define MB_UNSUPPORTED_FLAGS   ( MB_COMPULSORY_FLAGS & ~MB_SUPPORTED_FLAGS )

Multiboot flags that we don't support.

We only care about the compulsory feature flags (bits 0-15); we are allowed to ignore the optional feature flags.

Definition at line 91 of file multiboot.c.

Referenced by multiboot_exec().

mb_cmdlines

#define mb_cmdlines   __use_data16 ( mb_cmdlines )

Definition at line 95 of file multiboot.c.

Referenced by __bss16_array(), and multiboot_add_cmdline().

mbinfo

#define mbinfo   __use_data16 ( mbinfo )

Definition at line 257 of file multiboot.c.

Referenced by __bss16(), multiboot_add_modules(), multiboot_build_memmap(), and multiboot_exec().

mb_bootloader_name

#define mb_bootloader_name   __use_data16 ( mb_bootloader_name )

Definition at line 261 of file multiboot.c.

Referenced by __bss16_array(), and multiboot_exec().

mbmemmap

#define mbmemmap   __use_data16 ( mbmemmap )

Definition at line 265 of file multiboot.c.

Referenced by __bss16_array(), multiboot_build_memmap(), and multiboot_exec().

mbmodules

#define mbmodules   __use_data16 ( mbmodules )

Definition at line 269 of file multiboot.c.

Referenced by __bss16_array(), and multiboot_exec().

Function Documentation

FILE_LICENCE()

FILE_LICENCE

(

GPL2_OR_LATER_OR_UBDL

)

FEATURE()

FEATURE	(	FEATURE_IMAGE	,
		"MBOOT"	,
		DHCP_EB_FEATURE_MULTIBOOT	,
		1	)

References DHCP_EB_FEATURE_MULTIBOOT, and FEATURE_IMAGE.

__bss16_array() [1/4]

char __bss16_array ( mb_cmdlines )

static

Multiboot module command lines.

References mb_cmdlines, and MB_MAX_CMDLINE.

multiboot_build_memmap()

void multiboot_build_memmap ( struct image * image, struct multiboot_info * mbinfo, struct multiboot_memory_map * mbmemmap, unsigned int limit )

static

Build multiboot memory map.

Parameters

image	Multiboot image
mbinfo	Multiboot information structure
mbmemmap	Multiboot memory map
limit	Maxmimum number of memory map entries

Definition at line 108 of file multiboot.c.

                                                          {
        struct memmap_region region;
        unsigned int remaining;
 
        /* Translate into multiboot format */
        memset ( mbmemmap, 0, sizeof ( *mbmemmap ) );
        remaining = limit;
        for_each_memmap ( &region, 0 ) {
 
                /* Ignore any non-memory regions */
                if ( ! ( region.flags & MEMMAP_FL_MEMORY ) )
                        continue;
                DBGC_MEMMAP ( image, &region );
 
                /* Check Multiboot memory map limit */
                if ( ! remaining ) {
                        DBGC ( image, "MULTIBOOT %s limit of %d memmap "
                               "entries reached\n", image->name, limit );
                        break;
                }
 
                /* Populate Multiboot memory map entry */
                mbmemmap->size = ( sizeof ( *mbmemmap ) -
                                   sizeof ( mbmemmap->size ) );
                mbmemmap->base_addr = region.min;
                mbmemmap->length = memmap_size ( &region );
                mbmemmap->type = MBMEM_RAM;
 
                /* Update Multiboot information */
                mbinfo->mmap_length += sizeof ( *mbmemmap );
                if ( mbmemmap->base_addr == 0 )
                        mbinfo->mem_lower = ( mbmemmap->length / 1024 );
                if ( mbmemmap->base_addr == 0x100000 )
                        mbinfo->mem_upper = ( mbmemmap->length / 1024 );
 
                /* Move to next Multiboot memory map entry */
                mbmemmap++;
                remaining--;
        }
}

References DBGC, DBGC_MEMMAP, memmap_region::flags, for_each_memmap, limit, mbinfo, MBMEM_RAM, mbmemmap, MEMMAP_FL_MEMORY, memmap_size(), memset(), memmap_region::min, and image::name.

Referenced by multiboot_exec().

multiboot_add_cmdline()

physaddr_t multiboot_add_cmdline ( struct image * image )

static

Add command line in base memory.

Parameters

image

Image

Return values

physaddr

Physical address of command line

Definition at line 158 of file multiboot.c.

                                                                {
        char *mb_cmdline = ( mb_cmdlines + mb_cmdline_offset );
        size_t remaining = ( sizeof ( mb_cmdlines ) - mb_cmdline_offset );
        char *buf = mb_cmdline;
        size_t len;
 
        /* Copy image URI to base memory buffer as start of command line */
        len = ( format_uri ( image->uri, buf, remaining ) + 1 /* NUL */ );
        if ( len > remaining )
                len = remaining;
        mb_cmdline_offset += len;
        buf += len;
        remaining -= len;
 
        /* Copy command line to base memory buffer, if present */
        if ( image->cmdline ) {
                mb_cmdline_offset--; /* Strip NUL */
                buf--;
                remaining++;
                len = ( snprintf ( buf, remaining, " %s",
                                   image->cmdline ) + 1 /* NUL */ );
                if ( len > remaining )
                        len = remaining;
                mb_cmdline_offset += len;
        }
 
        return virt_to_phys ( mb_cmdline );
}

References image::cmdline, format_uri(), len, mb_cmdline_offset, mb_cmdlines, snprintf(), and image::uri.

Referenced by multiboot_exec().

multiboot_add_modules()

int multiboot_add_modules ( struct image * image, physaddr_t start, struct multiboot_info * mbinfo, struct multiboot_module * modules, unsigned int limit )

static

Add multiboot modules.

Parameters

image	Multiboot image
start	Start address for modules
mbinfo	Multiboot information structure
modules	Multiboot module list

Return values

rc	Return status code

Definition at line 196 of file multiboot.c.

                                                        {
        struct image *module_image;
        struct multiboot_module *module;
        int rc;
 
        /* Add each image as a multiboot module */
        for_each_image ( module_image ) {
 
                if ( mbinfo->mods_count >= limit ) {
                        DBGC ( image, "MULTIBOOT %s limit of %d modules "
                               "reached\n", image->name, limit );
                        break;
                }
 
                /* Skip hidden images */
                if ( module_image->flags & IMAGE_HIDDEN )
                        continue;
 
                /* Page-align the module */
                start = ( ( start + 0xfff ) & ~0xfff );
 
                /* Prepare segment */
                if ( ( rc = prep_segment ( phys_to_virt ( start ),
                                           module_image->len,
                                           module_image->len ) ) != 0 ) {
                        DBGC ( image, "MULTIBOOT %s could not prepare module "
                               "%s: %s\n", image->name, module_image->name,
                               strerror ( rc ) );
                        return rc;
                }
 
                /* Copy module */
                memcpy ( phys_to_virt ( start ), module_image->data,
                         module_image->len );
 
                /* Add module to list */
                module = &modules[mbinfo->mods_count++];
                module->mod_start = start;
                module->mod_end = ( start + module_image->len );
                module->string = multiboot_add_cmdline ( module_image );
                module->reserved = 0;
                DBGC ( image, "MULTIBOOT %s module %s is [%x,%x)\n",
                       image->name, module_image->name, module->mod_start,
                       module->mod_end );
                start += module_image->len;
        }
 
        return 0;
}

References image::data, DBGC, image::flags, for_each_image, IMAGE_HIDDEN, image::len, limit, mbinfo, memcpy(), multiboot_module::mod_end, multiboot_module::mod_start, image::name, prep_segment(), rc, start, and strerror().

Referenced by multiboot_exec().

__bss16()

struct multiboot_info __bss16 ( mbinfo )

static

The multiboot information structure.

Kept in base memory because some OSes won't find it elsewhere, along with the other structures belonging to the Multiboot information table.

References __bss16, and mbinfo.

__bss16_array() [2/4]

char __bss16_array ( mb_bootloader_name )

static

The multiboot bootloader name.

References mb_bootloader_name.

__bss16_array() [3/4]

struct multiboot_memory_map __bss16_array ( mbmemmap )

static

The multiboot memory map.

References __bss16_array, MAX_MEMMAP, and mbmemmap.

__bss16_array() [4/4]

struct multiboot_module __bss16_array ( mbmodules )

static

The multiboot module list.

References __bss16_array, MAX_MODULES, and mbmodules.

multiboot_find_header()

int multiboot_find_header ( struct image * image )

static

Find multiboot header.

Parameters

image

Multiboot file

Return values

offset

Offset to Multiboot header, or negative error

Definition at line 277 of file multiboot.c.

                                                         {
        const struct multiboot_header *mb;
        size_t offset;
        uint32_t checksum;
 
        /* Scan through first 8kB of image file */
        for ( offset = 0 ; offset < 8192 ; offset += 4 ) {
                /* Check for end of image */
                if ( ( offset + sizeof ( *mb ) ) > image->len )
                        break;
                mb = ( image->data + offset );
                /* Check signature */
                if ( mb->magic != MULTIBOOT_HEADER_MAGIC )
                        continue;
                /* Copy header and verify checksum */
                checksum = ( mb->magic + mb->flags + mb->checksum );
                if ( checksum != 0 )
                        continue;
                /* Return header */
                return offset;
        }
 
        /* No multiboot header found */
        DBGC ( image, "MULTIBOOT %s has no multiboot header\n",
               image->name );
        return -ENOEXEC;
}

References checksum, image::data, DBGC, ENOEXEC, image::len, mb(), MULTIBOOT_HEADER_MAGIC, image::name, and offset.

Referenced by multiboot_exec(), and multiboot_probe().

multiboot_load_raw()

int multiboot_load_raw ( struct image * image, size_t offset, physaddr_t * entry, physaddr_t * max )

static

Load raw multiboot image into memory.

Parameters

image	Multiboot image
offset	Offset to Multiboot header

Return values

entry	Entry point
max	Maximum used address
rc	Return status code

Definition at line 314 of file multiboot.c.

                                                                     {
        const struct multiboot_header *mb = ( image->data + offset );
        size_t filesz;
        size_t memsz;
        void *buffer;
        int rc;
 
        /* Sanity check */
        if ( ! ( mb->flags & MB_FLAG_RAW ) ) {
                DBGC ( image, "MULTIBOOT %s is not flagged as a raw image\n",
                       image->name );
                return -EINVAL;
        }
 
        /* Calculate starting offset within file */
        if ( ( mb->load_addr > mb->header_addr ) ||
             ( ( mb->header_addr - mb->load_addr ) > offset ) ) {
                DBGC ( image, "MULTIBOOT %s has misplaced header\n",
                       image->name );
                return -EINVAL;
        }
        offset -= ( mb->header_addr - mb->load_addr );
        assert ( offset < image->len );
 
        /* Calculate length of initialized data */
        filesz = ( mb->load_end_addr ?
                   ( mb->load_end_addr - mb->load_addr ) :
                   ( image->len - offset ) );
        if ( filesz > image->len ) {
                DBGC ( image, "MULTIBOOT %s has overlength data\n",
                       image->name );
                return -EINVAL;
        }
 
        /* Calculate length of uninitialised data */
        memsz = ( mb->bss_end_addr ?
                  ( mb->bss_end_addr - mb->load_addr ) : filesz );
        DBGC ( image, "MULTIBOOT %s loading [%zx,%zx) to [%x,%zx,%zx)\n",
               image->name, offset, ( offset + filesz ), mb->load_addr,
               ( mb->load_addr + filesz ), ( mb->load_addr + memsz ) );
 
        /* Verify and prepare segment */
        buffer = phys_to_virt ( mb->load_addr );
        if ( ( rc = prep_segment ( buffer, filesz, memsz ) ) != 0 ) {
                DBGC ( image, "MULTIBOOT %s could not prepare segment: %s\n",
                       image->name, strerror ( rc ) );
                return rc;
        }
 
        /* Copy image to segment */
        memcpy ( buffer, ( image->data + offset ), filesz );
 
        /* Record execution entry point and maximum used address */
        *entry = mb->entry_addr;
        *max = ( mb->load_addr + memsz );
 
        return 0;
}

References assert, buffer, image::data, DBGC, EINVAL, image::len, len, max, mb(), MB_FLAG_RAW, memcpy(), memsz, image::name, offset, prep_segment(), rc, and strerror().

Referenced by multiboot_exec().

multiboot_load_elf()

int multiboot_load_elf ( struct image * image, physaddr_t * entry, physaddr_t * max )

static

Load ELF multiboot image into memory.

Parameters

image

Multiboot file

Return values

entry	Entry point
max	Maximum used address
rc	Return status code

Definition at line 382 of file multiboot.c.

                                                  {
        int rc;
 
        /* Load ELF image*/
        if ( ( rc = elf_load ( image, entry, max ) ) != 0 ) {
                DBGC ( image, "MULTIBOOT %s ELF image failed to load: %s\n",
                       image->name, strerror ( rc ) );
                return rc;
        }
 
        return 0;
}

References DBGC, elf_load(), max, image::name, rc, and strerror().

Referenced by multiboot_exec().

multiboot_exec()

int multiboot_exec ( struct image * image )

static

Execute multiboot image.

Parameters

image

Multiboot image

Return values

rc	Return status code

Definition at line 402 of file multiboot.c.

                                                  {
        const struct multiboot_header *mb;
        physaddr_t entry;
        physaddr_t max;
        int offset;
        int rc;
 
        /* Locate multiboot header, if present */
        offset = multiboot_find_header ( image );
        if ( offset < 0 ) {
                rc = offset;
                return rc;
        }
        mb = ( image->data + offset );
 
        /* Abort if we detect flags that we cannot support */
        if ( mb->flags & MB_UNSUPPORTED_FLAGS ) {
                DBGC ( image, "MULTIBOOT %s flags %#08x not supported\n",
                       image->name, ( mb->flags & MB_UNSUPPORTED_FLAGS ) );
                return -ENOTSUP;
        }
 
        /* There is technically a bit MB_FLAG_RAW to indicate whether
         * this is an ELF or a raw image.  In practice, grub will use
         * the ELF header if present, and Solaris relies on this
         * behaviour.
         */
        if ( ( ( rc = multiboot_load_elf ( image, &entry, &max ) ) != 0 ) &&
             ( ( rc = multiboot_load_raw ( image, offset, &entry,
                                           &max ) ) != 0 ) ) {
                return rc;
        }
 
        /* Populate multiboot information structure */
        memset ( &mbinfo, 0, sizeof ( mbinfo ) );
        mbinfo.flags = ( MBI_FLAG_LOADER | MBI_FLAG_MEM | MBI_FLAG_MMAP |
                         MBI_FLAG_CMDLINE | MBI_FLAG_MODS );
        mb_cmdline_offset = 0;
        mbinfo.cmdline = multiboot_add_cmdline ( image );
        mbinfo.mods_addr = virt_to_phys ( mbmodules );
        mbinfo.mmap_addr = virt_to_phys ( mbmemmap );
        snprintf ( mb_bootloader_name, sizeof ( mb_bootloader_name ),
                   "iPXE %s", product_version );
        mbinfo.boot_loader_name = virt_to_phys ( mb_bootloader_name );
        if ( ( rc = multiboot_add_modules ( image, max, &mbinfo, mbmodules,
                                            ( sizeof ( mbmodules ) /
                                              sizeof ( mbmodules[0] ) ) ) ) !=0)
                return rc;
 
        /* Multiboot images may not return and have no callback
         * interface, so shut everything down prior to booting the OS.
         */
        shutdown_boot();
 
        /* Build memory map after unhiding bootloader memory regions as part of
         * shutting everything down.
         */
        multiboot_build_memmap ( image, &mbinfo, mbmemmap,
                                 ( sizeof(mbmemmap) / sizeof(mbmemmap[0]) ) );
 
        /* Jump to OS with flat physical addressing */
        DBGC ( image, "MULTIBOOT %s starting execution at %lx\n",
               image->name, entry );
        __asm__ __volatile__ ( PHYS_CODE ( "pushl %%ebp\n\t"
                                           "call *%%edi\n\t"
                                           "popl %%ebp\n\t" )
                               : : "a" ( MULTIBOOT_BOOTLOADER_MAGIC ),
                                   "b" ( virt_to_phys ( &mbinfo ) ),
                                   "D" ( entry )
                               : "ecx", "edx", "esi", "memory" );
 
        DBGC ( image, "MULTIBOOT %s returned\n", image->name );
 
        /* It isn't safe to continue after calling shutdown() */
        while ( 1 ) {}
 
        return -ECANCELED;  /* -EIMPOSSIBLE, anyone? */
}

References __asm__(), __volatile__(), image::data, DBGC, ECANCELED, ENOTSUP, max, mb(), mb_bootloader_name, mb_cmdline_offset, MB_UNSUPPORTED_FLAGS, MBI_FLAG_CMDLINE, MBI_FLAG_LOADER, MBI_FLAG_MEM, MBI_FLAG_MMAP, MBI_FLAG_MODS, mbinfo, mbmemmap, mbmodules, memset(), multiboot_add_cmdline(), multiboot_add_modules(), MULTIBOOT_BOOTLOADER_MAGIC, multiboot_build_memmap(), multiboot_find_header(), multiboot_load_elf(), multiboot_load_raw(), image::name, offset, PHYS_CODE, product_version, rc, shutdown_boot(), and snprintf().

Referenced by __image_type().

multiboot_probe()

int multiboot_probe ( struct image * image )

static

Probe multiboot image.

Parameters

image

Multiboot file

Return values

rc	Return status code

Definition at line 487 of file multiboot.c.

                                                   {
        const struct multiboot_header *mb;
        int offset;
        int rc;
 
        /* Locate multiboot header, if present */
        offset = multiboot_find_header ( image );
        if ( offset < 0 ) {
                rc = offset;
                return rc;
        }
        mb = ( image->data + offset );
        DBGC ( image, "MULTIBOOT %s found header at +%#x with flags %#08x\n",
               image->name, offset, mb->flags );
 
        return 0;
}

References image::data, DBGC, mb(), multiboot_find_header(), image::name, offset, and rc.

Referenced by __image_type().

__image_type()

struct image_type multiboot_image_type __image_type

(

PROBE_MULTIBOOT

)

Multiboot image type.

References __image_type, multiboot_exec(), multiboot_probe(), and PROBE_MULTIBOOT.

Variable Documentation

mb_cmdline_offset

unsigned int mb_cmdline_offset

static

Offset within module command lines.

Definition at line 98 of file multiboot.c.

Referenced by multiboot_add_cmdline(), and multiboot_exec().