Commit 8f9aeca7 authored by Bernhard Walle's avatar Bernhard Walle Committed by Andi Kleen
Browse files

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



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: default avatarBernhard Walle <bwalle@suse.de>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Cc: Alon Bar-Lev <alon.barlev@gmail.com>
Acked-by: default avatarH. Peter Anvin <hpa@zytor.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 79e03011

Documentation/i386/boot.txt

+17 −6
Original line number Diff line number Diff line
@@ -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

arch/i386/boot/setup.S

+6 −1
Original line number Diff line number Diff line
@@ -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

arch/x86_64/boot/setup.S

+6 −1
Original line number Diff line number Diff line
@@ -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

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