[PATCH 1/5] update boot spec to 2.07

Rusty Russell
2007-10-02T23:36:02Z

Proposed updates for version 2.07 of the boot protocol. This includes:

load_flags.KEEP_SEGMENTS- flag to request/inhibit segment reloads
hardware_subarch - what subarchitecture we're booting under
hardware_subarch_data - per-architecture data

The intention of these changes is to make booting a paravirtualized
kernel work via the normal Linux boot protocol. The intention is that
the bzImage payload can be a properly formed ELF file, so that the
bootloader can use its ELF notes and Phdrs to get more metadata about
the kernel and its requirements.

The ELF file could be the uncompressed kernel vmlinux itself; it would
only take small buildsystem changes to implement this.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Vivek Goyal <vgoyal@in.ibm.com>

---
Documentation/i386/boot.txt | 34 +++++++++++++++++++++++++++++++++-
arch/i386/kernel/asm-offsets.c | 7 +++++++
include/asm-i386/bootparam.h | 9 +++++++--
3 files changed, 47 insertions(+), 3 deletions(-)

diff -r cff7afab3bac Documentation/i386/boot.txt
--- a/Documentation/i386/boot.txt Tue Oct 02 22:05:10 2007 +1000
+++ b/Documentation/i386/boot.txt Tue Oct 02 22:05:10 2007 +1000
@@ -168,6 +168,8 @@ 0234/1 2.05+ relocatable_kernel Whether
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
+023C/4 2.07+ hardware_subarch Hardware subarchitecture
+0240/8 2.07+ hardware_subarch_data Subarchitecture-specific data

(1) For backwards compatibility, if the setup_sects field contains 0, the
real value is 4.
@@ -204,7 +206,7 @@ boot loaders can ignore those fields.

The byte order of all fields is littleendian (this is x86, after all.)

-Field name: setup_secs
+Field name: setup_sects
Type: read
Offset/size: 0x1f1/1
Protocol: ALL
@@ -356,6 +358,13 @@ Protocol: 2.00+
- If 0, the protected-mode code is loaded at 0x10000.
- If 1, the protected-mode code is loaded at 0x100000.

+ Bit 6 (write): KEEP_SEGMENTS
+ Protocol: 2.07+
+ - if 0, reload the segment registers in the 32bit entry point.
+ - if 1, do not reload the segment registers in the 32bit entry point.
+ Assume that %cs %ds %ss %es are all set to flat segments with
+ a base of 0 (or the equivalent for their environment).
+
Bit 7 (write): CAN_USE_HEAP
Set this bit to 1 to indicate that the value entered in the
heap_end_ptr is valid. If this field is clear, some setup code
@@ -479,6 +488,29 @@ Protocol: 2.06+
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.
+
+Field name: hardware_subarch
+Type: write
+Offset/size: 0x23c/4
+Protocol: 2.07+
+
+ In a paravirtualized environment the hardware low level architectural
+ pieces such as interrupt handling, page table handling, and
+ accessing process control registers needs to be done differently.
+
+ This field allows the bootloader to inform the kernel we are in one
+ one of those environments.
+
+ 0x00000000 The default x86/PC environment
+ 0x00000001 lguest
+ 0x00000002 Xen
+
+Field name: hardware_subarch_data
+Type: write
+Offset/size: 0x240/8
+Protocol: 2.07+
+
+ A pointer to data that is specific to hardware subarch

**** THE KERNEL COMMAND LINE
diff -r cff7afab3bac arch/i386/kernel/asm-offsets.c
--- a/arch/i386/kernel/asm-offsets.c Tue Oct 02 22:05:10 2007 +1000
+++ b/arch/i386/kernel/asm-offsets.c Tue Oct 02 22:05:10 2007 +1000
@@ -15,6 +15,7 @@
#include <asm/fixmap.h>
#include <asm/processor.h>
#include <asm/thread_info.h>
+#include <asm/bootparam.h>
#include <asm/elf.h>

#include <xen/interface/xen.h>
@@ -145,4 +146,10 @@ void foo(void)
OFFSET(LGUEST_PAGES_regs_errcode, lguest_pages, regs.errcode);
OFFSET(LGUEST_PAGES_regs, lguest_pages, regs);
#endif
+
+ BLANK();
+ OFFSET(BP_scratch, boot_params, scratch);
+ OFFSET(BP_loadflags, boot_params, hdr.loadflags);
+ OFFSET(BP_hardware_subarch, boot_params, hdr.hardware_subarch);
+ OFFSET(BP_version, boot_params, hdr.version);
}
diff -r cff7afab3bac include/asm-i386/bootparam.h
--- a/include/asm-i386/bootparam.h Tue Oct 02 22:05:10 2007 +1000
+++ b/include/asm-i386/bootparam.h Tue Oct 02 22:05:10 2007 +1000
@@ -25,8 +25,9 @@ struct setup_header {
u16 kernel_version;
u8 type_of_loader;
u8 loadflags;
-#define LOADED_HIGH 0x01
-#define CAN_USE_HEAP 0x80
+#define LOADED_HIGH (1<<0)
+#define KEEP_SEGMENTS (1<<6)
+#define CAN_USE_HEAP (1<<7)
u16 setup_move_size;
u32 code32_start;
u32 ramdisk_image;
@@ -38,6 +39,10 @@ struct setup_header {
u32 initrd_addr_max;
u32 kernel_alignment;
u8 relocatable_kernel;
+ u8 _pad2[3];
+ u32 cmdline_size;
+ u32 hardware_subarch;
+ u64 hardware_subarch_data;
} __attribute__((packed));

struct sys_desc_table {