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

[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
......@@ -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
......@@ -129,8 +130,12 @@ 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
real value is 4.
(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
......@@ -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
......
......@@ -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
......
......@@ -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 */
......
......@@ -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
......
......@@ -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 */
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment