I'm proposing the attached patch to replace Frank Sorenson's
i386-buildc-write-out-larger-system-size-to-bootsector patch currently
in -mm. The goal (presumably) is to make the bzImage format
self-terminating.
Signed-off-by: H. Peter Anvin <[email protected]>
diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt
--- a/Documentation/i386/boot.txt
+++ b/Documentation/i386/boot.txt
@@ -2,7 +2,7 @@
----------------------------
H. Peter Anvin <[email protected]>
- 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)
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.
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 follow
**** 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 foll
**** 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
diff --git a/arch/i386/boot/setup.S b/arch/i386/boot/setup.S
--- a/arch/i386/boot/setup.S
+++ b/arch/i386/boot/setup.S
@@ -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
diff --git a/arch/i386/boot/tools/build.c b/arch/i386/boot/tools/build.c
--- a/arch/i386/boot/tools/build.c
+++ b/arch/i386/boot/tools/build.c
@@ -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 */
diff --git a/arch/x86_64/boot/setup.S b/arch/x86_64/boot/setup.S
--- a/arch/x86_64/boot/setup.S
+++ b/arch/x86_64/boot/setup.S
@@ -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
diff --git a/arch/x86_64/boot/tools/build.c b/arch/x86_64/boot/tools/build.c
--- a/arch/x86_64/boot/tools/build.c
+++ b/arch/x86_64/boot/tools/build.c
@@ -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 */
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