Commit f8eeaaf4 authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Linus Torvalds
Browse files

[PATCH] Make the bzImage format self-terminating 



Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
Cc: Frank Sorenson <frank@tuxrocks.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 5e1efe49

Documentation/i386/boot.txt

+22 −13
Original line number Diff line number Diff line
@@ -2,7 +2,7 @@ 
		     ----------------------------



		    H. Peter Anvin <hpa@zytor.com>

			Last update 2002-01-01

			Last update 2005-09-02



On the i386 platform, the Linux kernel uses a rather complicated boot

convention.  This has evolved partially due to historical aspects, as
@@ -34,6 +34,8 @@ Protocol 2.02: (Kernel 2.4.0-test3-pre3) New command line protocol. 
Protocol 2.03:	(Kernel 2.4.18-pre1) Explicitly makes the highest possible

		initrd address available to the bootloader.



Protocol 2.04:	(Kernel 2.6.14) Extend the syssize field to four bytes.





**** MEMORY LAYOUT
@@ -103,10 +105,9 @@ The header looks like: 
Offset	Proto	Name		Meaning

/Size



01F1/1	ALL	setup_sects	The size of the setup in sectors

01F1/1	ALL(1	setup_sects	The size of the setup in sectors

01F2/2	ALL	root_flags	If set, the root is mounted readonly

01F4/2	ALL	syssize		DO NOT USE - for bootsect.S use only

01F6/2	ALL	swap_dev	DO NOT USE - obsolete

01F4/4	2.04+(2	syssize		The size of the 32-bit code in 16-byte paras

01F8/2	ALL	ram_size	DO NOT USE - for bootsect.S use only

01FA/2	ALL	vid_mode	Video mode control

01FC/2	ALL	root_dev	Default root device number
@@ -129,9 +130,13 @@ Offset Proto Name Meaning 
0228/4	2.02+	cmd_line_ptr	32-bit pointer to the kernel command line

022C/4	2.03+	initrd_addr_max	Highest legal initrd address



For backwards compatibility, if the setup_sects field contains 0, the

(1) For backwards compatibility, if the setup_sects field contains 0, the

    real value is 4.



(2) For boot protocol prior to 2.04, the upper two bytes of the syssize

    field are unusable, which means the size of a bzImage kernel

    cannot be determined.



If the "HdrS" (0x53726448) magic number is not found at offset 0x202,

the boot protocol version is "old".  Loading an old kernel, the

following parameters should be assumed:
@@ -230,12 +235,16 @@ loader to communicate with the kernel. Some of its options are also 
relevant to the boot loader itself, see "special command line options"

below.



The kernel command line is a null-terminated string up to 255

characters long, plus the final null.

The kernel command line is a null-terminated string currently up to

255 characters long, plus the final null.  A string that is too long

will be automatically truncated by the kernel, a boot loader may allow

a longer command line to be passed to permit future kernels to extend

this limit.



If the boot protocol version is 2.02 or later, the address of the

kernel command line is given by the header field cmd_line_ptr (see

above.)

above.)  This address can be anywhere between the end of the setup

heap and 0xA0000.



If the protocol version is *not* 2.02 or higher, the kernel

command line is entered using the following protocol:
@@ -255,7 +264,7 @@ command line is entered using the following protocol: 
**** SAMPLE BOOT CONFIGURATION



As a sample configuration, assume the following layout of the real

mode segment:

mode segment (this is a typical, and recommended layout):



	0x0000-0x7FFF	Real mode kernel

	0x8000-0x8FFF	Stack and heap
@@ -312,9 +321,9 @@ Such a boot loader should enter the following fields in the header: 


**** LOADING THE REST OF THE KERNEL



The non-real-mode kernel starts at offset (setup_sects+1)*512 in the

kernel file (again, if setup_sects == 0 the real value is 4.)  It

should be loaded at address 0x10000 for Image/zImage kernels and

The 32-bit (non-real-mode) kernel starts at offset (setup_sects+1)*512

in the kernel file (again, if setup_sects == 0 the real value is 4.)

It should be loaded at address 0x10000 for Image/zImage kernels and

0x100000 for bzImage kernels.



The kernel is a bzImage kernel if the protocol >= 2.00 and the 0x01

arch/i386/boot/setup.S

+1 −1
Original line number Diff line number Diff line
@@ -82,7 +82,7 @@ start: 
# This is the setup header, and it must start at %cs:2 (old 0x9020:2)



		.ascii	"HdrS"		# header signature

		.word	0x0203		# header version number (>= 0x0105)

		.word	0x0204		# header version number (>= 0x0105)

					# or else old loadlin-1.5 will fail)

realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG

start_sys_seg:	.word	SYSSEG

arch/i386/boot/tools/build.c

+3 −1
Original line number Diff line number Diff line
@@ -177,7 +177,9 @@ int main(int argc, char ** argv) 
		die("Output: seek failed");

	buf[0] = (sys_size & 0xff);

	buf[1] = ((sys_size >> 8) & 0xff);

	if (write(1, buf, 2) != 2)

	buf[2] = ((sys_size >> 16) & 0xff);

	buf[3] = ((sys_size >> 24) & 0xff);

	if (write(1, buf, 4) != 4)

		die("Write of image length failed");



	return 0;					    /* Everything is OK */

arch/x86_64/boot/setup.S

+1 −1
Original line number Diff line number Diff line
@@ -81,7 +81,7 @@ start: 
# This is the setup header, and it must start at %cs:2 (old 0x9020:2)



		.ascii	"HdrS"		# header signature

		.word	0x0203		# header version number (>= 0x0105)

		.word	0x0204		# header version number (>= 0x0105)

					# or else old loadlin-1.5 will fail)

realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG

start_sys_seg:	.word	SYSSEG

arch/x86_64/boot/tools/build.c

+3 −1
Original line number Diff line number Diff line
@@ -178,7 +178,9 @@ int main(int argc, char ** argv) 
		die("Output: seek failed");

	buf[0] = (sys_size & 0xff);

	buf[1] = ((sys_size >> 8) & 0xff);

	if (write(1, buf, 2) != 2)

	buf[2] = ((sys_size >> 16) & 0xff);

	buf[3] = ((sys_size >> 24) & 0xff);

	if (write(1, buf, 4) != 4)

		die("Write of image length failed");



	return 0;					    /* Everything is OK */