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authorH. Peter Anvin <hpa@zytor.com>2009-05-12 01:06:23 +0200
committerH. Peter Anvin <hpa@zytor.com>2009-05-12 02:45:05 +0200
commitd297366ba692faf1f0384811a6ff0b20c3470b1b (patch)
tree08a041463badb70f45491fdbceb0c54a5ab5597d
parentx86, boot: make kernel_alignment adjustable; new bzImage fields (diff)
downloadlinux-d297366ba692faf1f0384811a6ff0b20c3470b1b.tar.xz
linux-d297366ba692faf1f0384811a6ff0b20c3470b1b.zip
x86: document new bzImage fields
Document the new bzImage fields for kernel memory placement. [ Impact: adds documentation ] Signed-off-by: H. Peter Anvin <hpa@zytor.com>
-rw-r--r--Documentation/x86/boot.txt69
1 files changed, 65 insertions, 4 deletions
diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index e0203662f9e9..cf8dfc70a118 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -50,6 +50,11 @@ Protocol 2.08: (Kernel 2.6.26) Added crc32 checksum and ELF format
Protocol 2.09: (Kernel 2.6.26) Added a field of 64-bit physical
pointer to single linked list of struct setup_data.
+Protocol 2.10: (Kernel 2.6.31) A protocol for relaxed alignment
+ beyond the kernel_alignment added, new init_size and
+ pref_address fields.
+
+
**** MEMORY LAYOUT
The traditional memory map for the kernel loader, used for Image or
@@ -173,7 +178,7 @@ Offset Proto Name Meaning
022C/4 2.03+ ramdisk_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
-0235/1 N/A pad2 Unused
+0235/1 2.10+ min_alignment Minimum alignment, as a power of two
0236/2 N/A pad3 Unused
0238/4 2.06+ cmdline_size Maximum size of the kernel command line
023C/4 2.07+ hardware_subarch Hardware subarchitecture
@@ -182,6 +187,8 @@ Offset Proto Name Meaning
024C/4 2.08+ payload_length Length of kernel payload
0250/8 2.09+ setup_data 64-bit physical pointer to linked list
of struct setup_data
+0258/8 2.10+ pref_address Preferred loading address
+0260/4 2.10+ init_size Linear memory required during initialization
(1) For backwards compatibility, if the setup_sects field contains 0, the
real value is 4.
@@ -482,11 +489,19 @@ Protocol: 2.03+
0x37FFFFFF, you can start your ramdisk at 0x37FE0000.)
Field name: kernel_alignment
-Type: read (reloc)
+Type: read/modify (reloc)
Offset/size: 0x230/4
-Protocol: 2.05+
+Protocol: 2.05+ (read), 2.10+ (modify)
+
+ Alignment unit required by the kernel (if relocatable_kernel is
+ true.) A relocatable kernel that is loaded at an alignment
+ incompatible with the value in this field will be realigned during
+ kernel initialization.
- Alignment unit required by the kernel (if relocatable_kernel is true.)
+ Starting with protocol version 2.10, this reflects the kernel
+ alignment preferred for optimal performance; it is possible for the
+ loader to modify this field to permit a lesser alignment. See the
+ min_alignment and pref_address field below.
Field name: relocatable_kernel
Type: read (reloc)
@@ -498,6 +513,22 @@ Protocol: 2.05+
After loading, the boot loader must set the code32_start field to
point to the loaded code, or to a boot loader hook.
+Field name: min_alignment
+Type: read (reloc)
+Offset/size: 0x235/1
+Protocol: 2.10+
+
+ This field, if nonzero, indicates as a power of two the minimum
+ alignment required, as opposed to preferred, by the kernel to boot.
+ If a boot loader makes use of this field, it should update the
+ kernel_alignment field with the alignment unit desired; typically:
+
+ kernel_alignment = 1 << min_alignment
+
+ There may be a considerable performance cost with an excessively
+ misaligned kernel. Therefore, a loader should typically try each
+ power-of-two alignment from kernel_alignment down to this alignment.
+
Field name: cmdline_size
Type: read
Offset/size: 0x238/4
@@ -582,6 +613,36 @@ Protocol: 2.09+
sure to consider the case where the linked list already contains
entries.
+Field name: pref_address
+Type: read (reloc)
+Offset/size: 0x258/8
+Protocol: 2.10+
+
+ This field, if nonzero, represents a preferred load address for the
+ kernel. A relocating bootloader should attempt to load at this
+ address if possible.
+
+ A non-relocatable kernel will unconditionally move itself and to run
+ at this address.
+
+Field name: init_size
+Type: read
+Offset/size: 0x25c/4
+
+ This field indicates the amount of linear contiguous memory starting
+ at the kernel runtime start address that the kernel needs before it
+ is capable of examining its memory map. This is not the same thing
+ as the total amount of memory the kernel needs to boot, but it can
+ be used by a relocating boot loader to help select a safe load
+ address for the kernel.
+
+ The kernel runtime start address is determined by the following algorithm:
+
+ if (relocatable_kernel)
+ runtime_start = align_up(load_address, kernel_alignment)
+ else
+ runtime_start = pref_address
+
**** THE IMAGE CHECKSUM