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[PATCH] x86: add command line length to boot protocol

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Because the command line is increased to 2048 characters after 2.6.21, it's
not possible for boot loaders and userspace tools to determine the length
of the command line the kernel can understand.  The benefit of knowing the
length is that users can be warned if the command line size is too long
which prevents surprise if things don't work after bootup.

This patch updates the boot protocol to contain a field called
"cmdline_size" that contain the length of the command line (excluding the
terminating zero).

The patch also adds missing fields (of protocol version 2.05) to the x86_64
setup code.

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Alon Bar-Lev <alon.barlev@gmail.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Bernhard Walle 2007-05-02 19:27:10 +02:00 committed by Andi Kleen
parent 79e030114a
commit 8f9aeca7a0
3 changed files with 29 additions and 8 deletions
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23
Documentation/i386/boot.txt
View File

@ -2,7 +2,7 @@
----------------------------
H. Peter Anvin <hpa@zytor.com>
Last update 2007-01-26
Last update 2007-03-06
On the i386 platform, the Linux kernel uses a rather complicated boot
convention. This has evolved partially due to historical aspects, as
@ -35,9 +35,13 @@ 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.
Protocol 2.05: (Kernel 2.6.20) Make protected mode kernel relocatable.
Introduce relocatable_kernel and kernel_alignment fields.
Protocol 2.06: (Kernel 2.6.22) Added a field that contains the size of
the boot command line
**** MEMORY LAYOUT
@ -133,6 +137,8 @@ Offset Proto Name Meaning
022C/4 2.03+ initrd_addr_max Highest legal initrd address
0230/4 2.05+ kernel_alignment Physical addr alignment required for kernel
0234/1 2.05+ relocatable_kernel Whether kernel is relocatable or not
0235/3 N/A pad2 Unused
0238/4 2.06+ cmdline_size Maximum size of the kernel command line
(1) For backwards compatibility, if the setup_sects field contains 0, the
real value is 4.
@ -233,6 +239,12 @@ filled out, however:
if your ramdisk is exactly 131072 bytes long and this field is
0x37FFFFFF, you can start your ramdisk at 0x37FE0000.)
cmdline_size:
The maximum size of the command line without the terminating
zero. This means that the command line can contain at most
cmdline_size characters. With protocol version 2.05 and
earlier, the maximum size was 255.
**** THE KERNEL COMMAND LINE
@ -241,11 +253,10 @@ 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 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.
The kernel command line is a null-terminated string. The maximum
length can be retrieved from the field cmdline_size. Before protocol
version 2.06, the maximum was 255 characters. A string that is too
long will be automatically truncated by the kernel.
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

7
arch/i386/boot/setup.S
View File

@ -52,6 +52,7 @@
#include <asm/boot.h>
#include <asm/e820.h>
#include <asm/page.h>
#include <asm/setup.h>
/* Signature words to ensure LILO loaded us right */
#define SIG1 0xAA55
@ -81,7 +82,7 @@ start:
# This is the setup header, and it must start at %cs:2 (old 0x9020:2)
.ascii "HdrS" # header signature
.word 0x0205 # header version number (>= 0x0105)
.word 0x0206 # 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
@ -171,6 +172,10 @@ relocatable_kernel: .byte 0
pad2: .byte 0
pad3: .word 0
cmdline_size: .long COMMAND_LINE_SIZE-1 #length of the command line,
#added with boot protocol
#version 2.06
trampoline: call start_of_setup
.align 16
# The offset at this point is 0x240

7
arch/x86_64/boot/setup.S
View File

@ -51,6 +51,7 @@
#include <asm/boot.h>
#include <asm/e820.h>
#include <asm/page.h>
#include <asm/setup.h>
/* Signature words to ensure LILO loaded us right */
#define SIG1 0xAA55
@ -80,7 +81,7 @@ start:
# This is the setup header, and it must start at %cs:2 (old 0x9020:2)
.ascii "HdrS" # header signature
.word 0x0205 # header version number (>= 0x0105)
.word 0x0206 # 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
@ -165,6 +166,10 @@ relocatable_kernel: .byte 0
pad2: .byte 0
pad3: .word 0
cmdline_size: .long COMMAND_LINE_SIZE-1 #length of the command line,
#added with boot protocol
#version 2.06
trampoline: call start_of_setup
.align 16
# The offset at this point is 0x240