This patch:
a) Bumps the boot protocol version number to 2.03;
b) Adds a field to the boot header which contains the maximum legal
initrd address;
c) Slightly reorganizes a couple of macros to make (b) possible;
d) Documents this change and the actual behaviour for previous
protocol versions.
The patch is against 2.4.17-pre6, but applies to 2.5.1-pre8 as well.
-hpa
diff -ur stock3/linux-2.4.17-pre6/Documentation/i386/boot.txt linux-2.4.17-pre6/Documentation/i386/boot.txt
--- stock3/linux-2.4.17-pre6/Documentation/i386/boot.txt Wed Nov 7 14:46:01 2001
+++ linux-2.4.17-pre6/Documentation/i386/boot.txt Sun Dec 9 01:12:01 2001
@@ -2,7 +2,7 @@
----------------------------
H. Peter Anvin <hpa@zytor.com>
- Last update 2000-10-29
+ Last update 2001-12-09
On the i386 platform, the Linux kernel uses a rather complicated boot
convention. This has evolved partially due to historical aspects, as
@@ -25,12 +25,15 @@
Protocol 2.01: (Kernel 1.3.76) Added a heap overrun warning.
Protocol 2.02: (Kernel 2.4.0-test3-pre3) New command line protocol.
- Lower the conventional memory ceiling. No overwrite
+ Lower the conventional memory ceiling. No overwrite
of the traditional setup area, thus making booting
safe for systems which use the EBDA from SMM or 32-bit
BIOS entry points. zImage deprecated but still
supported.
+Protocol 2.03: (???) Explicitly makes the highest possible initrd address
+ available to the bootloader.
+
**** MEMORY LAYOUT
@@ -45,7 +48,7 @@
098000 +------------------------+
| Kernel setup | The kernel real-mode code.
090200 +------------------------+
- | Kernel boot sector | The kernel legacy boot sector.
+ | Kernel boot sector | The kernel legacy boot sector.
090000 +------------------------+
| Protected-mode kernel | The bulk of the kernel image.
010000 +------------------------+
@@ -62,7 +65,7 @@
When using bzImage, the protected-mode kernel was relocated to
0x100000 ("high memory"), and the kernel real-mode block (boot sector,
setup, and stack/heap) was made relocatable to any address between
-0x10000 and end of low memory. Unfortunately, in protocols 2.00 and
+0x10000 and end of low memory. Unfortunately, in protocols 2.00 and
2.01 the command line is still required to live in the 0x9XXXX memory
range, and that memory range is still overwritten by the early kernel.
The 2.02 protocol fixes that.
@@ -71,7 +74,7 @@
low memory touched by the boot loader -- as low as possible, since
some newer BIOSes have begun to allocate some rather large amounts of
memory, called the Extended BIOS Data Area, near the top of low
-memory. The boot loader should use the "INT 12h" BIOS call to verify
+memory. The boot loader should use the "INT 12h" BIOS call to verify
how much low memory is available.
Unfortunately, if INT 12h reports that the amount of memory is too
@@ -123,6 +126,7 @@
0224/2 2.01+ heap_end_ptr Free memory after setup end
0226/2 N/A pad1 Unused
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.
@@ -180,9 +184,9 @@
The initrd should typically be located as high in memory as
possible, as it may otherwise get overwritten by the early
- kernel initialization sequence. However, it must never be
- located above address 0x3C000000 if you want all kernels to
- read it.
+ kernel initialization sequence. However, it must never be
+ located above the address specified in the initrd_addr_max
+ field. The initrd should be at least 4K page aligned.
cmd_line_ptr:
If the protocol version is 2.02 or higher, this is a 32-bit
@@ -192,7 +196,15 @@
command line, in which case you can point this to an empty
string (or better yet, to the string "auto".) If this field
is left at zero, the kernel will assume that your boot loader
- does not support the 2.02 protocol.
+ does not support the 2.02+ protocol.
+
+ ramdisk_max:
+ The maximum address that may be occupied by the initrd
+ contents. For boot protocols 2.02 or earlier, this field is
+ not present, and the maximum address is 0x37FFFFFF. (This
+ address is defined as the address of the highest safe byte, so
+ if your ramdisk is exactly 131072 bytes long and this field is
+ 0x37FFFFFF, you can start your ramdisk at 0x37FE0000.)
**** THE KERNEL COMMAND LINE
@@ -254,14 +266,14 @@
if ( protocol >= 0x0202 ) {
cmd_line_ptr = base_ptr + 0x9000;
} else {
- cmd_line_magic = 0xA33F;
+ cmd_line_magic = 0xA33F;
cmd_line_offset = 0x9000;
setup_move_size = 0x9100;
}
} else {
/* Very old kernel */
- cmd_line_magic = 0xA33F;
+ cmd_line_magic = 0xA33F;
cmd_line_offset = 0x9000;
/* A very old kernel MUST have its real-mode code
@@ -411,4 +423,3 @@
After completing your hook, you should jump to the address
that was in this field before your boot loader overwrote it.
-
diff -ur stock3/linux-2.4.17-pre6/arch/i386/boot/setup.S linux-2.4.17-pre6/arch/i386/boot/setup.S
--- stock3/linux-2.4.17-pre6/arch/i386/boot/setup.S Sat Dec 8 23:48:42 2001
+++ linux-2.4.17-pre6/arch/i386/boot/setup.S Sun Dec 9 01:05:29 2001
@@ -50,7 +50,8 @@
#include <linux/compile.h>
#include <asm/boot.h>
#include <asm/e820.h>
-
+#include <asm/page.h>
+
/* Signature words to ensure LILO loaded us right */
#define SIG1 0xAA55
#define SIG2 0x5A5A
@@ -79,7 +80,7 @@
# This is the setup header, and it must start at %cs:2 (old 0x9020:2)
.ascii "HdrS" # header signature
- .word 0x0202 # header version number (>= 0x0105)
+ .word 0x0203 # 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
@@ -153,6 +154,10 @@
# can be located anywhere in
# low memory 0x10000 or higher.
+ramdisk_max: .long __MAXMEM-1 # (Header version 0x0203 or later)
+ # The highest safe address for
+ # the contents of an initrd
+
trampoline: call start_of_setup
.space 1024
# End of setup header #####################################################
@@ -539,7 +544,7 @@
cmpw $0, %cs:realmode_swtch
jz rmodeswtch_normal
- lcall *%cs:realmode_swtch
+ lcall %cs:realmode_swtch
jmp rmodeswtch_end
diff -ur stock3/linux-2.4.17-pre6/arch/i386/kernel/setup.c linux-2.4.17-pre6/arch/i386/kernel/setup.c
--- stock3/linux-2.4.17-pre6/arch/i386/kernel/setup.c Sat Dec 8 23:48:42 2001
+++ linux-2.4.17-pre6/arch/i386/kernel/setup.c Sun Dec 9 00:45:42 2001
@@ -827,10 +827,8 @@
#define PFN_PHYS(x) ((x) << PAGE_SHIFT)
/*
- * 128MB for vmalloc and initrd
+ * Reserved space for vmalloc and iomap - defined in asm/page.h
*/
-#define VMALLOC_RESERVE (unsigned long)(128 << 20)
-#define MAXMEM (unsigned long)(-PAGE_OFFSET-VMALLOC_RESERVE)
#define MAXMEM_PFN PFN_DOWN(MAXMEM)
#define MAX_NONPAE_PFN (1 << 20)
diff -ur stock3/linux-2.4.17-pre6/include/asm-i386/page.h linux-2.4.17-pre6/include/asm-i386/page.h
--- stock3/linux-2.4.17-pre6/include/asm-i386/page.h Thu Nov 22 11:46:18 2001
+++ linux-2.4.17-pre6/include/asm-i386/page.h Sun Dec 9 00:51:43 2001
@@ -80,6 +80,12 @@
#define __PAGE_OFFSET (0xC0000000)
+/*
+ * This much address space is reserved for vmalloc() and iomap()
+ * as well as fixmap mappings.
+ */
+#define __VMALLOC_RESERVE (128 << 20)
+
#ifndef __ASSEMBLY__
/*
@@ -118,6 +124,9 @@
#endif /* __ASSEMBLY__ */
#define PAGE_OFFSET ((unsigned long)__PAGE_OFFSET)
+#define VMALLOC_RESERVE ((unsigned long)__VMALLOC_RESERVE)
+#define __MAXMEM (-__PAGE_OFFSET-__VMALLOC_RESERVE)
+#define MAXMEM ((unsigned long)(-PAGE_OFFSET-VMALLOC_RESERVE))
#define __pa(x) ((unsigned long)(x)-PAGE_OFFSET)
#define __va(x) ((void *)((unsigned long)(x)+PAGE_OFFSET))
#define virt_to_page(kaddr) (mem_map + (__pa(kaddr) >> PAGE_SHIFT))
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