[PATCH RFC 0/7] proposed updates to boot protocol and paravirt booting

[PATCH RFC 0/7] proposed updates to boot protocol and paravirt booting

[Jeremy Fitzhardinge]

This series:
 1. Updates the boot protocol to version 2.07
 2. Clean up the existing build process, to get rid of tools/build and
    make the linker do more heavy lifting
 3. Make the bzImage payload an ELF file.  The bootloader can extract
    this as a naked ELF file by skipping over boot_params.setup_sects worth
    of 16-bit setup code.
 4. Update the boot_params to 2.07, and update the kernel's head.S to
    jump to the appropriate subarch-specific kernel entrypoint.  The
    very earliest code is common (copy boot_params, clear bss); the
    split happens just before the initial pagetable setup.
+ random little changes to make it all hang together

This boots native for me, so everything basically works.  But I haven't
tested it end-to-end yet, because I haven't done the Xen bits yet.
Perhaps Rusty can do the lguest version to verify that its all sound in
principle (hint hint ;).

So, how does it look?

	J
-- 

[PATCH RFC 1/7] update boot spec to 2.07

[Jeremy Fitzhardinge]

[-- Attachment #1: update-boot-spec.patch --]
[-- Type: text/plain, Size: 5422 bytes --]

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
kernel_payload		- address of the raw kernel blob

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.

kernel_payload was added so that a bootloader can just get to the raw
bits of the kernel, so that it can do its own decompression/relocation
if it wishes.  This is not particularly well-defined yet; I just added
it with the hope that it keeps HPA happy.

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

---
 Documentation/i386/boot.txt    |   43 +++++++++++++++++++++++++++++++++++++++-
 arch/i386/kernel/asm-offsets.c |    7 ++++++
 include/asm-i386/bootparam.h   |   10 +++++++--
 3 files changed, 57 insertions(+), 3 deletions(-)

===================================================================
--- a/Documentation/i386/boot.txt
+++ b/Documentation/i386/boot.txt
@@ -168,6 +168,9 @@ 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
+0248/4	2.07+	kernel_payload	Pointer to raw kernel data
 
 (1) For backwards compatibility, if the setup_sects field contains 0, the
     real value is 4.
@@ -204,7 +207,7 @@ 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 +359,13 @@ 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 +489,37 @@ 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
+
+Field name:	kernel_payload
+Type:		read
+Offset/size:	0x248/4
+Protocol:	2.07+
+
+  The relocated pointer to the actual kernel payload, in whatever form
+  it exists in (gzip image, normally).
 
 
 **** THE KERNEL COMMAND LINE
===================================================================
--- a/arch/i386/kernel/asm-offsets.c
+++ b/arch/i386/kernel/asm-offsets.c
@@ -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>
 
@@ -143,4 +144,10 @@ 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);
 }
===================================================================
--- a/include/asm-i386/bootparam.h
+++ b/include/asm-i386/bootparam.h
@@ -24,8 +24,9 @@ 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;
@@ -37,6 +38,11 @@ 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;
+	u32	kernel_payload;
 } __attribute__((packed));
 
 struct sys_desc_table {

-- 

[PATCH RFC 2/7] add WEAK() for creating weak asm labels

[Jeremy Fitzhardinge]

[-- Attachment #1: weak-linkage.patch --]
[-- Type: text/plain, Size: 467 bytes --]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>

---
 include/linux/linkage.h |    6 ++++++
 1 file changed, 6 insertions(+)

===================================================================
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -34,6 +34,12 @@
   name:
 #endif
 
+#ifndef WEAK
+#define WEAK(name)	   \
+	.weak name;	   \
+	name:
+#endif
+
 #define KPROBE_ENTRY(name) \
   .pushsection .kprobes.text, "ax"; \
   ENTRY(name)

-- 

[PATCH RFC 3/7] allow linux/elf.h to be included in assembler

[Jeremy Fitzhardinge]

[-- Attachment #1: asm-elf_h.patch --]
[-- Type: text/plain, Size: 3726 bytes --]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>

---
 include/linux/elf.h |   24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

===================================================================
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -1,9 +1,10 @@
 #ifndef _LINUX_ELF_H
 #define _LINUX_ELF_H
 
+#include <linux/elf-em.h>
+#ifndef __ASSEMBLY__
 #include <linux/types.h>
 #include <linux/auxvec.h>
-#include <linux/elf-em.h>
 #include <asm/elf.h>
 
 struct file;
@@ -31,6 +32,7 @@ typedef __u32	Elf64_Word;
 typedef __u32	Elf64_Word;
 typedef __u64	Elf64_Xword;
 typedef __s64	Elf64_Sxword;
+#endif	/* __ASSEMBLY__ */
 
 /* These constants are for the segment types stored in the image headers */
 #define PT_NULL    0
@@ -123,6 +125,7 @@ typedef __s64	Elf64_Sxword;
 #define ELF64_ST_BIND(x)	ELF_ST_BIND(x)
 #define ELF64_ST_TYPE(x)	ELF_ST_TYPE(x)
 
+#ifndef __ASSEMBLY__
 typedef struct dynamic{
   Elf32_Sword d_tag;
   union{
@@ -138,6 +141,7 @@ typedef struct {
     Elf64_Addr d_ptr;
   } d_un;
 } Elf64_Dyn;
+#endif	/* __ASSEMBLY__ */
 
 /* The following are used with relocations */
 #define ELF32_R_SYM(x) ((x) >> 8)
@@ -146,6 +150,7 @@ typedef struct {
 #define ELF64_R_SYM(i)			((i) >> 32)
 #define ELF64_R_TYPE(i)			((i) & 0xffffffff)
 
+#ifndef __ASSEMBLY__
 typedef struct elf32_rel {
   Elf32_Addr	r_offset;
   Elf32_Word	r_info;
@@ -185,11 +190,12 @@ typedef struct elf64_sym {
   Elf64_Addr st_value;		/* Value of the symbol */
   Elf64_Xword st_size;		/* Associated symbol size */
 } Elf64_Sym;
-
+#endif	/* __ASSEMBLY__ */
 
 #define EI_NIDENT	16
 
-typedef struct elf32_hdr{
+#ifndef __ASSEMBLY__
+typedef struct elf32_hdr {
   unsigned char	e_ident[EI_NIDENT];
   Elf32_Half	e_type;
   Elf32_Half	e_machine;
@@ -222,6 +228,7 @@ typedef struct elf64_hdr {
   Elf64_Half e_shnum;
   Elf64_Half e_shstrndx;
 } Elf64_Ehdr;
+#endif	/* __ASSEMBLY__ */
 
 /* These constants define the permissions on sections in the program
    header, p_flags. */
@@ -229,7 +236,8 @@ typedef struct elf64_hdr {
 #define PF_W		0x2
 #define PF_X		0x1
 
-typedef struct elf32_phdr{
+#ifndef __ASSEMBLY__
+typedef struct elf32_phdr {
   Elf32_Word	p_type;
   Elf32_Off	p_offset;
   Elf32_Addr	p_vaddr;
@@ -250,6 +258,7 @@ typedef struct elf64_phdr {
   Elf64_Xword p_memsz;		/* Segment size in memory */
   Elf64_Xword p_align;		/* Segment alignment, file & memory */
 } Elf64_Phdr;
+#endif	/* __ASSEMBLY__ */
 
 /* sh_type */
 #define SHT_NULL	0
@@ -284,7 +293,8 @@ typedef struct elf64_phdr {
 #define SHN_ABS		0xfff1
 #define SHN_COMMON	0xfff2
 #define SHN_HIRESERVE	0xffff
- 
+
+#ifndef __ASSEMBLY__
 typedef struct {
   Elf32_Word	sh_name;
   Elf32_Word	sh_type;
@@ -310,6 +320,7 @@ typedef struct elf64_shdr {
   Elf64_Xword sh_addralign;	/* Section alignment */
   Elf64_Xword sh_entsize;	/* Entry size if section holds table */
 } Elf64_Shdr;
+#endif	/* __ASSEMBLY__ */
 
 #define	EI_MAG0		0		/* e_ident[] indexes */
 #define	EI_MAG1		1
@@ -343,6 +354,7 @@ typedef struct elf64_shdr {
 
 #define ELFOSABI_NONE	0
 #define ELFOSABI_LINUX	3
+#define ELFOSABI_STANDALONE	255
 
 #ifndef ELF_OSABI
 #define ELF_OSABI ELFOSABI_NONE
@@ -357,6 +369,7 @@ typedef struct elf64_shdr {
 #define NT_PRXFPREG     0x46e62b7f      /* copied from gdb5.1/include/elf/common.h */
 
 
+#ifndef __ASSEMBLY__
 /* Note header in a PT_NOTE section */
 typedef struct elf32_note {
   Elf32_Word	n_namesz;	/* Name size */
@@ -396,5 +409,6 @@ static inline void arch_write_notes(stru
 #define ELF_CORE_EXTRA_NOTES_SIZE arch_notes_size()
 #define ELF_CORE_WRITE_EXTRA_NOTES arch_write_notes(file)
 #endif /* ARCH_HAVE_EXTRA_ELF_NOTES */
+#endif	/* __ASSEMBLY__ */
 
 #endif /* _LINUX_ELF_H */

-- 

[PATCH RFC 4/7] define ELF notes for adding to a boot image

[Jeremy Fitzhardinge]

[-- Attachment #1: elf-bootnotes.patch --]
[-- Type: text/plain, Size: 889 bytes --]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Vivek Goyal <vgoyal@in.ibm.com>

---
 include/linux/elf_boot.h |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

===================================================================
--- /dev/null
+++ b/include/linux/elf_boot.h
@@ -0,0 +1,15 @@
+#ifndef ELF_BOOT_H
+#define ELF_BOOT_H
+
+/* Elf notes to help bootloaders identify what program they are booting.
+ */
+
+/* Standardized Elf image notes for booting... The name for all of these is ELFBoot */
+#define ELF_NOTE_BOOT		ELFBoot
+
+#define EIN_PROGRAM_NAME	1 /* The program in this ELF file */
+#define EIN_PROGRAM_VERSION	2 /* The version of the program in this ELF file */
+#define EIN_PROGRAM_CHECKSUM	3 /* ip style checksum of the memory image. */
+#define EIN_ARGUMENT_STYLE	4 /* String identifying argument passing style */
+
+#endif /* ELF_BOOT_H */

-- 

[PATCH RFC 5/7] i386: clean up bzImage generation

[Jeremy Fitzhardinge]

[-- Attachment #1: i386-cleanup-image-generation.patch --]
[-- Type: text/plain, Size: 13162 bytes --]

This patch cleans up image generation in several ways:
 - Firstly, it removes tools/build, and uses binutils to do all the
   final construction of the bzImage.  This removes a chunk of code
   and makes the image generation more flexible, since we can compute
   various numbers rather than be forced to use fixed constants.

 - Rename compressed/vmlinux to compressed/blob, to make it a
   bit clearer that it's the compressed kernel image + decompressor
   (now all the files named "vmlinux*" are directly derived from
   the kernel vmlinux).

 - Rather than using objcopy to wrap the compressed kernel into an
   object file, simply use the assembler: payload.S does a .incbin
   of the blob.bin file, which allows us to easily place
   it into a section, and it makes the Makefile dependency a little
   clearer.

 - Similarly, use the same technique to create compressed/piggy.o,
   which cleans things up even more, since the .S file can also
   set the input and output_size symbols without further linker
   script hackery; it also removes a complete linker script.

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

---
 arch/i386/boot/Makefile               |   31 +-----
 arch/i386/boot/compressed/Makefile    |   13 --
 arch/i386/boot/compressed/piggy.S     |   10 +
 arch/i386/boot/compressed/vmlinux.scr |   10 -
 arch/i386/boot/header.S               |    6 -
 arch/i386/boot/payload.S              |    3 
 arch/i386/boot/setup.ld               |   39 ++++---
 arch/i386/boot/tools/.gitignore       |    1 
 arch/i386/boot/tools/build.c          |  168 ---------------------------------
 9 files changed, 56 insertions(+), 225 deletions(-)

===================================================================
--- a/arch/i386/boot/Makefile
+++ b/arch/i386/boot/Makefile
@@ -25,12 +25,13 @@ SVGA_MODE := -DSVGA_MODE=NORMAL_VGA
 
 #RAMDISK := -DRAMDISK=512
 
-targets		:= vmlinux.bin setup.bin setup.elf zImage bzImage
+targets		:= blob.bin setup.elf zImage bzImage
 subdir- 	:= compressed
 
 setup-y		+= a20.o apm.o cmdline.o copy.o cpu.o cpucheck.o edd.o
-setup-y		+= header.o main.o mca.o memory.o pm.o pmjump.o
-setup-y		+= printf.o string.o tty.o video.o version.o voyager.o
+setup-y		+= header.o main.o mca.o memory.o payload.o pm.o
+setup-y		+= pmjump.o printf.o string.o tty.o video.o version.o
+setup-y		+= voyager.o
 
 # The link order of the video-*.o modules can matter.  In particular,
 # video-vga.o *must* be listed first, followed by video-vesa.o.
@@ -39,10 +40,6 @@ setup-y		+= video-vga.o
 setup-y		+= video-vga.o
 setup-y		+= video-vesa.o
 setup-y		+= video-bios.o
-
-hostprogs-y	:= tools/build
-
-HOSTCFLAGS_build.o := $(LINUXINCLUDE)
 
 # ---------------------------------------------------------------------------
 
@@ -65,18 +62,12 @@ AFLAGS		:= $(CFLAGS) -D__ASSEMBLY__
 $(obj)/bzImage: IMAGE_OFFSET := 0x100000
 $(obj)/bzImage: EXTRA_CFLAGS := -D__BIG_KERNEL__
 $(obj)/bzImage: EXTRA_AFLAGS := $(SVGA_MODE) $(RAMDISK) -D__BIG_KERNEL__
-$(obj)/bzImage: BUILDFLAGS   := -b
 
-quiet_cmd_image = BUILD   $@
-cmd_image = $(obj)/tools/build $(BUILDFLAGS) $(obj)/setup.bin \
-	    $(obj)/vmlinux.bin $(ROOT_DEV) > $@
-
-$(obj)/zImage $(obj)/bzImage: $(obj)/setup.bin \
-			      $(obj)/vmlinux.bin $(obj)/tools/build FORCE
-	$(call if_changed,image)
+$(obj)/zImage $(obj)/bzImage: $(obj)/setup.elf FORCE
+	$(call if_changed,objcopy)
 	@echo 'Kernel: $@ is ready' ' (#'`cat .version`')'
 
-$(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE
+$(obj)/blob.bin: $(obj)/compressed/blob FORCE
 	$(call if_changed,objcopy)
 
 SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))
@@ -85,12 +76,10 @@ LDFLAGS_setup.elf	:= -T
 $(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
 	$(call if_changed,ld)
 
-OBJCOPYFLAGS_setup.bin	:= -O binary
+$(obj)/payload.o:	EXTRA_AFLAGS := -Wa,-I$(obj)
+$(obj)/payload.o: $(src)/payload.S $(obj)/blob.bin
 
-$(obj)/setup.bin: $(obj)/setup.elf FORCE
-	$(call if_changed,objcopy)
-
-$(obj)/compressed/vmlinux: FORCE
+$(obj)/compressed/blob: FORCE
 	$(Q)$(MAKE) $(build)=$(obj)/compressed IMAGE_OFFSET=$(IMAGE_OFFSET) $@
 
 # Set this if you want to pass append arguments to the zdisk/fdimage/isoimage kernel
===================================================================
--- a/arch/i386/boot/compressed/Makefile
+++ b/arch/i386/boot/compressed/Makefile
@@ -4,11 +4,10 @@
 # create a compressed vmlinux image from the original vmlinux
 #
 
-targets		:= vmlinux vmlinux.bin vmlinux.bin.gz head.o misc.o piggy.o \
+targets		:= blob vmlinux.bin vmlinux.bin.gz head.o misc.o piggy.o \
 			vmlinux.bin.all vmlinux.relocs
-EXTRA_AFLAGS	:= -traditional
 
-LDFLAGS_vmlinux := -T
+LDFLAGS_blob	:= -T
 hostprogs-y	:= relocs
 
 CFLAGS  := -m32 -D__KERNEL__ $(LINUX_INCLUDE) -O2 \
@@ -17,7 +16,7 @@ CFLAGS  := -m32 -D__KERNEL__ $(LINUX_INC
 	   $(call cc-option,-fno-stack-protector)
 LDFLAGS := -m elf_i386
 
-$(obj)/vmlinux: $(src)/vmlinux.lds $(obj)/head.o $(obj)/misc.o $(obj)/piggy.o FORCE
+$(obj)/blob: $(src)/vmlinux.lds $(obj)/head.o $(obj)/misc.o $(obj)/piggy.o FORCE
 	$(call if_changed,ld)
 	@:
 
@@ -44,7 +43,5 @@ else
 	$(call if_changed,gzip)
 endif
 
-LDFLAGS_piggy.o := -r --format binary --oformat elf32-i386 -T
-
-$(obj)/piggy.o: $(src)/vmlinux.scr $(obj)/vmlinux.bin.gz FORCE
-	$(call if_changed,ld)
+$(obj)/piggy.o:	EXTRA_AFLAGS := -Wa,-I$(obj)
+$(obj)/piggy.o: $(obj)/vmlinux.bin.gz
===================================================================
--- /dev/null
+++ b/arch/i386/boot/compressed/piggy.S
@@ -0,0 +1,10 @@
+.section .data.compressed,"a",@progbits
+
+.globl input_data, input_len, output_len
+
+input_len:	.long input_data_end - input_data
+
+input_data:
+.incbin "vmlinux.bin.gz"
+output_len = .-4
+input_data_end:
===================================================================
--- a/arch/i386/boot/compressed/vmlinux.scr
+++ /dev/null
@@ -1,10 +0,0 @@
-SECTIONS
-{
-  .data.compressed : {
-	input_len = .;
-	LONG(input_data_end - input_data) input_data = .; 
-	*(.data) 
-	output_len = . - 4;
-	input_data_end = .; 
-	}
-}
===================================================================
--- a/arch/i386/boot/header.S
+++ b/arch/i386/boot/header.S
@@ -97,9 +97,9 @@ bugger_off_msg:
 	.section ".header", "a"
 	.globl	hdr
 hdr:
-setup_sects:	.byte SETUPSECTS
+setup_sects:	.byte _setup_sects
 root_flags:	.word ROOT_RDONLY
-syssize:	.long SYSSIZE
+syssize:	.long kernel_size_para
 ram_size:	.word RAMDISK
 vid_mode:	.word SVGA_MODE
 root_dev:	.word ROOT_DEV
@@ -148,7 +148,7 @@ CAN_USE_HEAP	= 0x80			# If set, the load
 		.byte	LOADED_HIGH
 #endif
 
-setup_move_size: .word  0x8000		# size to move, when setup is not
+setup_move_size: .word  _setup_size	# size to move, when setup is not
 					# loaded at 0x90000. We will move setup
 					# to 0x90000 then just before jumping
 					# into the kernel. However, only the
===================================================================
--- /dev/null
+++ b/arch/i386/boot/payload.S
@@ -0,0 +1,3 @@
+.section .kernel,"a",@progbits
+
+.incbin "blob.bin"
===================================================================
--- a/arch/i386/boot/setup.ld
+++ b/arch/i386/boot/setup.ld
@@ -3,18 +3,16 @@
  *
  * Linker script for the i386 setup code
  */
-OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
+OUTPUT_FORMAT("elf32-i386")
 OUTPUT_ARCH(i386)
 ENTRY(_start)
 
 SECTIONS
 {
-	. = 0;
-	.bstext		: { *(.bstext) }
+	.bstext 0	: { *(.bstext) }
 	.bsdata		: { *(.bsdata) }
 
-	. = 497;
-	.header		: { *(.header) }
+	.header 497	: { *(.header) }
 	.inittext	: { *(.inittext) }
 	.initdata	: { *(.initdata) }
 	.text		: { *(.text*) }
@@ -38,16 +36,29 @@ SECTIONS
 
 
 	. = ALIGN(16);
-	__bss_start = .;
-	.bss 		:
-	{
-		*(.bss)
-	}
-	. = ALIGN(16);
-	_end = .;
+	.bss ALIGN(16)	: {
+		__bss_start = .;
+		 *(.bss)
+		. = ALIGN(16);
+		_end = .;
+	 }
 
 	/DISCARD/ : { *(.note*) }
 
-	. = ASSERT(_end <= 0x8000, "Setup too big!");
-	. = ASSERT(hdr == 0x1f1, "The setup header has the wrong offset!");
+	. = ALIGN(512);		/* align to sector size */
+	_setup_size = . - _start;
+	_setup_sects = _setup_size / 512;
+
+	/* compressed kernel data */
+	.kernel	: {
+		kernel = .;
+		*(.kernel)
+		kernel_end = .;
+
+	}
+	kernel_size = kernel_end - kernel;
+	kernel_size_para = (kernel_size + 15) / 16;
 }
+
+ASSERT(_end <= 0x8000, "Setup too big!");
+ASSERT(hdr == 0x1f1, "The setup header has the wrong offset!");
===================================================================
--- a/arch/i386/boot/tools/.gitignore
+++ /dev/null
@@ -1,1 +0,0 @@
-build
===================================================================
--- a/arch/i386/boot/tools/build.c
+++ /dev/null
@@ -1,168 +0,0 @@
-/*
- *  Copyright (C) 1991, 1992  Linus Torvalds
- *  Copyright (C) 1997 Martin Mares
- *  Copyright (C) 2007 H. Peter Anvin
- */
-
-/*
- * This file builds a disk-image from three different files:
- *
- * - setup: 8086 machine code, sets up system parm
- * - system: 80386 code for actual system
- *
- * It does some checking that all files are of the correct type, and
- * just writes the result to stdout, removing headers and padding to
- * the right amount. It also writes some system data to stderr.
- */
-
-/*
- * Changes by tytso to allow root device specification
- * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
- * Cross compiling fixes by Gertjan van Wingerde, July 1996
- * Rewritten by Martin Mares, April 1997
- * Substantially overhauled by H. Peter Anvin, April 2007
- */
-
-#include <stdio.h>
-#include <string.h>
-#include <stdlib.h>
-#include <stdarg.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/sysmacros.h>
-#include <unistd.h>
-#include <fcntl.h>
-#include <sys/mman.h>
-#include <asm/boot.h>
-
-typedef unsigned char  u8;
-typedef unsigned short u16;
-typedef unsigned long  u32;
-
-#define DEFAULT_MAJOR_ROOT 0
-#define DEFAULT_MINOR_ROOT 0
-
-/* Minimal number of setup sectors */
-#define SETUP_SECT_MIN 5
-#define SETUP_SECT_MAX 64
-
-/* This must be large enough to hold the entire setup */
-u8 buf[SETUP_SECT_MAX*512];
-int is_big_kernel;
-
-static void die(const char * str, ...)
-{
-	va_list args;
-	va_start(args, str);
-	vfprintf(stderr, str, args);
-	fputc('\n', stderr);
-	exit(1);
-}
-
-static void usage(void)
-{
-	die("Usage: build [-b] setup system [rootdev] [> image]");
-}
-
-int main(int argc, char ** argv)
-{
-	unsigned int i, sz, setup_sectors;
-	int c;
-	u32 sys_size;
-	u8 major_root, minor_root;
-	struct stat sb;
-	FILE *file;
-	int fd;
-	void *kernel;
-
-	if (argc > 2 && !strcmp(argv[1], "-b"))
-	  {
-	    is_big_kernel = 1;
-	    argc--, argv++;
-	  }
-	if ((argc < 3) || (argc > 4))
-		usage();
-	if (argc > 3) {
-		if (!strcmp(argv[3], "CURRENT")) {
-			if (stat("/", &sb)) {
-				perror("/");
-				die("Couldn't stat /");
-			}
-			major_root = major(sb.st_dev);
-			minor_root = minor(sb.st_dev);
-		} else if (strcmp(argv[3], "FLOPPY")) {
-			if (stat(argv[3], &sb)) {
-				perror(argv[3]);
-				die("Couldn't stat root device.");
-			}
-			major_root = major(sb.st_rdev);
-			minor_root = minor(sb.st_rdev);
-		} else {
-			major_root = 0;
-			minor_root = 0;
-		}
-	} else {
-		major_root = DEFAULT_MAJOR_ROOT;
-		minor_root = DEFAULT_MINOR_ROOT;
-	}
-	fprintf(stderr, "Root device is (%d, %d)\n", major_root, minor_root);
-
-	/* Copy the setup code */
-	file = fopen(argv[1], "r");
-	if (!file)
-		die("Unable to open `%s': %m", argv[1]);
-	c = fread(buf, 1, sizeof(buf), file);
-	if (ferror(file))
-		die("read-error on `setup'");
-	if (c < 1024)
-		die("The setup must be at least 1024 bytes");
-	if (buf[510] != 0x55 || buf[511] != 0xaa)
-		die("Boot block hasn't got boot flag (0xAA55)");
-	fclose(file);
-
-	/* Pad unused space with zeros */
-	setup_sectors = (c + 511) / 512;
-	if (setup_sectors < SETUP_SECT_MIN)
-		setup_sectors = SETUP_SECT_MIN;
-	i = setup_sectors*512;
-	memset(buf+c, 0, i-c);
-
-	/* Set the default root device */
-	buf[508] = minor_root;
-	buf[509] = major_root;
-
-	fprintf(stderr, "Setup is %d bytes (padded to %d bytes).\n", c, i);
-
-	/* Open and stat the kernel file */
-	fd = open(argv[2], O_RDONLY);
-	if (fd < 0)
-		die("Unable to open `%s': %m", argv[2]);
-	if (fstat(fd, &sb))
-		die("Unable to stat `%s': %m", argv[2]);
-	sz = sb.st_size;
-	fprintf (stderr, "System is %d kB\n", (sz+1023)/1024);
-	kernel = mmap(NULL, sz, PROT_READ, MAP_SHARED, fd, 0);
-	if (kernel == MAP_FAILED)
-		die("Unable to mmap '%s': %m", argv[2]);
-	sys_size = (sz + 15) / 16;
-	if (!is_big_kernel && sys_size > DEF_SYSSIZE)
-		die("System is too big. Try using bzImage or modules.");
-
-	/* Patch the setup code with the appropriate size parameters */
-	buf[0x1f1] = setup_sectors-1;
-	buf[0x1f4] = sys_size;
-	buf[0x1f5] = sys_size >> 8;
-	buf[0x1f6] = sys_size >> 16;
-	buf[0x1f7] = sys_size >> 24;
-
-	if (fwrite(buf, 1, i, stdout) != i)
-		die("Writing setup failed");
-
-	/* Copy the kernel code */
-	if (fwrite(kernel, 1, sz, stdout) != sz)
-		die("Writing kernel failed");
-	close(fd);
-
-	/* Everything is OK */
-	return 0;
-}

-- 

[PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[Jeremy Fitzhardinge]

[-- Attachment #1: i386-bzimage-elf-payload.patch --]
[-- Type: text/plain, Size: 10723 bytes --]

This patch makes the payload of the bzImage file an ELF file.  In
other words, the bzImage is structured as follows:
 - boot sector
 - 16bit setup code
 - ELF header
  - decompressor
  - compressed kernel

A bootloader may find the start of the ELF file by looking at the
setup_size entry in the boot params, and using that to find the offset
of the ELF header.  The ELF Phdrs contain all the mapped memory
required to decompress and start booting the kernel.

One slightly complex part of this is that the bzImage boot_params need
to know about the internal structure of the ELF file, at least to the
extent of being able to point the core32_start entry at the ELF file's
entrypoint, so that loaders which use this field will still work.

Similarly, the ELF header needs to know how big the kernel vmlinux's
bss segment is, in order to make sure is is mapped properly.

To handle these two cases, we generate abstracted versions of the
object files which only contain the symbols we care about (generated
with objcopy --strip-all --keep-symbol=X), and then include those
symbol tables with ld -R.

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

---
 arch/i386/boot/Makefile               |   11 ++++--
 arch/i386/boot/compressed/Makefile    |   29 +++++++++++++--
 arch/i386/boot/compressed/elfhdr.S    |   60 +++++++++++++++++++++++++++++++++
 arch/i386/boot/compressed/head.S      |    9 ++--
 arch/i386/boot/compressed/notes.S     |    7 +++
 arch/i386/boot/compressed/vmlinux.lds |   24 ++++++++++---
 arch/i386/boot/header.S               |    7 ---
 arch/i386/boot/setup.ld               |    5 ++
 arch/i386/kernel/head.S               |    1 
 arch/i386/kernel/vmlinux.lds.S        |    1 
 10 files changed, 131 insertions(+), 23 deletions(-)

===================================================================
--- a/arch/i386/boot/Makefile
+++ b/arch/i386/boot/Makefile
@@ -72,14 +72,19 @@ AFLAGS		:= $(CFLAGS) -D__ASSEMBLY__
 
 SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))
 
-LDFLAGS_setup.elf	:= -T
-$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
+$(obj)/zImage $(obj)/bzImage: 				\
+	LDFLAGS	:=					\
+		-R $(obj)/compressed/blob-syms		\
+		--defsym IMAGE_OFFSET=$(IMAGE_OFFSET) -T
+
+$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) 	\
+		$(obj)/compressed/blob-syms FORCE
 	$(call if_changed,ld)
 
 $(obj)/payload.o:	EXTRA_AFLAGS := -Wa,-I$(obj)
 $(obj)/payload.o: $(src)/payload.S $(obj)/blob.bin
 
-$(obj)/compressed/blob: FORCE
+$(obj)/compressed/blob $(obj)/compressed/blob-syms: FORCE
 	$(Q)$(MAKE) $(build)=$(obj)/compressed IMAGE_OFFSET=$(IMAGE_OFFSET) $@
 
 # Set this if you want to pass append arguments to the zdisk/fdimage/isoimage kernel
===================================================================
--- a/arch/i386/boot/compressed/Makefile
+++ b/arch/i386/boot/compressed/Makefile
@@ -4,21 +4,42 @@
 # create a compressed vmlinux image from the original vmlinux
 #
 
-targets		:= blob vmlinux.bin vmlinux.bin.gz head.o misc.o piggy.o \
+targets		:= blob vmlinux.bin vmlinux.bin.gz \
+			elfhdr.o head.o misc.o notes.o piggy.o \
 			vmlinux.bin.all vmlinux.relocs
 
-LDFLAGS_blob	:= -T
 hostprogs-y	:= relocs
 
 CFLAGS  := -m32 -D__KERNEL__ $(LINUX_INCLUDE) -O2 \
 	   -fno-strict-aliasing -fPIC \
 	   $(call cc-option,-ffreestanding) \
 	   $(call cc-option,-fno-stack-protector)
-LDFLAGS := -m elf_i386
+LDFLAGS := -R $(obj)/vmlinux-syms --defsym IMAGE_OFFSET=$(IMAGE_OFFSET) -T
 
-$(obj)/blob: $(src)/vmlinux.lds $(obj)/head.o $(obj)/misc.o $(obj)/piggy.o FORCE
+OBJS=$(addprefix $(obj)/,elfhdr.o head.o misc.o notes.o piggy.o)
+
+$(obj)/blob: $(src)/vmlinux.lds $(obj)/vmlinux-syms $(OBJS) FORCE
 	$(call if_changed,ld)
 	@:
+
+# Generate a stripped-down object including only the symbols needed
+# so that we can get them with ld -R. Direct stderr to /dev/null to
+# shut useless warning up.
+quiet_cmd_symextract = SYMEXT $@
+      cmd_symextract = objcopy -S \
+			$(addprefix -j,$(EXTRACTSECTS)) \
+			$(addprefix -K,$(EXTRACTSYMS)) \
+			$< $@ 2>/dev/null
+
+$(obj)/blob-syms: EXTRACTSYMS := blob_entry blob_payload
+$(obj)/blob-syms: EXTRACTSECTS := .text.head .data.compressed
+$(obj)/blob-syms: $(obj)/blob FORCE
+	$(call if_changed,symextract)
+
+$(obj)/vmlinux-syms: EXTRACTSYMS := __reserved_end
+$(obj)/vmlinux-syms: EXTRACTSECTS := .bss
+$(obj)/vmlinux-syms: vmlinux FORCE
+	$(call if_changed,symextract)
 
 $(obj)/vmlinux.bin: vmlinux FORCE
 	$(call if_changed,objcopy)
===================================================================
--- /dev/null
+++ b/arch/i386/boot/compressed/elfhdr.S
@@ -0,0 +1,60 @@
+/* DIY ELF header */
+
+#include <linux/elf.h>
+#include <asm/boot.h>
+
+.section .elfhdr,"a",@progbits
+ehdr:
+	# e_ident
+	.byte ELFMAG0, ELFMAG1, ELFMAG2, ELFMAG3
+	.byte ELFCLASS32, ELFDATA2LSB, EV_CURRENT, ELFOSABI_STANDALONE
+	.org ehdr + EI_NIDENT
+#ifndef CONFIG_RELOCATABLE
+	.word ET_EXEC				# e_type
+#else
+	.word ET_DYN				# e_type
+#endif
+	.word EM_386				# e_machine
+	.int  1					# e_version
+	.int  LOAD_PHYSICAL_ADDR + blob_startup_32 - ehdr	# e_entry
+	.int  phdr - ehdr			# e_phoff
+	.int  0					# e_shoff
+	.int  0					# e_flags
+	.word ehdr_end - ehdr			# e_ehsize
+	.word phdr_size				# e_phentsize
+	.word phnum				# e_phnum
+	.word 40				# e_shentsize
+	.word 0					# e_shnum
+	.word 0					# e_shstrndx
+ehdr_end:
+
+phdr:
+	.int PT_LOAD					# p_type
+	.int _head - ehdr				# p_offset
+	.int LOAD_PHYSICAL_ADDR				# p_vaddr
+	.int LOAD_PHYSICAL_ADDR				# p_paddr
+	.int blob_filesz				# p_filesz
+	.int blob_memsz					# p_memsz
+	.int PF_R | PF_W | PF_X				# p_flags
+	.int 4096					# p_align
+phdr_size = . - phdr
+
+	.int PT_NOTE					# p_type
+	.int _notes - ehdr				# p_offset
+	.int 0						# p_vaddr
+	.int 0						# p_paddr
+	.int blob_notesz				# p_filesz
+	.int 0						# p_memsz
+	.int 0						# p_flags
+	.int 0						# p_align
+
+	.int PT_PHDR					# p_type
+	.int phdr - ehdr				# p_offset
+	.int LOAD_PHYSICAL_ADDR + phdr - ehdr		# p_vaddr
+	.int LOAD_PHYSICAL_ADDR + phdr - ehdr		# p_paddr
+	.int phdr_end - phdr				# p_filesz
+	.int phdr_end - phdr				# p_memsz
+	.int PF_R | PF_W | PF_X				# p_flags
+	.int 0						# p_align
+phdr_end:
+phnum = (phdr_end - phdr) / phdr_size
===================================================================
--- a/arch/i386/boot/compressed/head.S
+++ b/arch/i386/boot/compressed/head.S
@@ -27,11 +27,12 @@
 #include <asm/segment.h>
 #include <asm/page.h>
 #include <asm/boot.h>
+#include <asm/asm-offsets.h>
 
 .section ".text.head","ax",@progbits
-	.globl startup_32
+	.globl blob_startup_32
 
-startup_32:
+blob_startup_32:
 	cld
 	cli
 	movl $(__BOOT_DS),%eax
@@ -48,7 +49,7 @@ startup_32:
  * data at 0x1e4 (defined as a scratch field) are used as the stack
  * for this calculation. Only 4 bytes are needed.
  */
-	leal (0x1e4+4)(%esi), %esp
+	leal (BP_scratch+4)(%esi), %esp
 	call 1f
 1:	popl %ebp
 	subl $1b, %ebp
@@ -85,7 +86,7 @@ 1:	popl %ebp
 	pushl %esi
 	leal _end(%ebp), %esi
 	leal _end(%ebx), %edi
-	movl $(_end - startup_32), %ecx
+	movl $(_end - blob_startup_32), %ecx
 	std
 	rep
 	movsb
===================================================================
--- /dev/null
+++ b/arch/i386/boot/compressed/notes.S
@@ -0,0 +1,7 @@
+#include <linux/elfnote.h>
+#include <linux/elf_boot.h>
+#include <linux/utsrelease.h>
+
+ELFNOTE(ELF_NOTE_BOOT, EIN_PROGRAM_NAME, .asciz "Linux")
+ELFNOTE(ELF_NOTE_BOOT, EIN_PROGRAM_VERSION, .asciz UTS_RELEASE)
+ELFNOTE(ELF_NOTE_BOOT, EIN_ARGUMENT_STYLE, .asciz "Linux")
===================================================================
--- a/arch/i386/boot/compressed/vmlinux.lds
+++ b/arch/i386/boot/compressed/vmlinux.lds
@@ -1,18 +1,21 @@ OUTPUT_FORMAT("elf32-i386", "elf32-i386"
-OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
+OUTPUT_FORMAT("elf32-i386")
 OUTPUT_ARCH(i386)
-ENTRY(startup_32)
+
 SECTIONS
 {
-        /* Be careful parts of head.S assume startup_32 is at
-         * address 0.
-	 */
+	/* make sure we don't get anything from vmlinux-syms */
+	/DISCARD/ : { */vmlinux-syms(*) }
+
 	. =  0 	;
 	.text.head : {
+		*(.elfhdr)
 		_head = . ;
+	blob_entry = blob_startup_32 + IMAGE_OFFSET;
 		*(.text.head)
 		_ehead = . ;
 	}
 	.data.compressed : {
+	blob_payload = input_data + IMAGE_OFFSET;
 		*(.data.compressed)
 	}
 	.text :	{
@@ -33,6 +36,7 @@ SECTIONS
 		*(.data.*)
 		_edata = . ;
 	}
+	blob_filesz = . ;
 	.bss : {
 		_bss = . ;
 		*(.bss)
@@ -40,4 +44,14 @@ SECTIONS
 		*(COMMON)
 		_end = . ;
 	}
+
+	/* __reserved_end taken from vmlinux */
+	blob_memsz = __reserved_end;
+
+	.notes : {
+		_notes = . ;
+		*(.note*)
+		_notes_end = .;
+	}
+	blob_notesz = _notes_end - _notes;
 }
===================================================================
--- a/arch/i386/boot/header.S
+++ b/arch/i386/boot/header.S
@@ -155,13 +155,8 @@ setup_move_size: .word  _setup_size	# si
 					# loader knows how much data behind
 					# us also needs to be loaded.
 
-code32_start:				# here loaders can put a different
+code32_start:	.long blob_entry	# here loaders can put a different
 					# start address for 32-bit code.
-#ifndef __BIG_KERNEL__
-		.long	0x1000		#   0x1000 = default for zImage
-#else
-		.long	0x100000	# 0x100000 = default for big kernel
-#endif
 
 ramdisk_image:	.long	0		# address of loaded ramdisk image
 					# Here the loader puts the 32-bit
===================================================================
--- a/arch/i386/boot/setup.ld
+++ b/arch/i386/boot/setup.ld
@@ -9,6 +9,9 @@ ENTRY(_start)
 
 SECTIONS
 {
+	/* make sure we don't get anything from blob-syms */
+	/DISCARD/	: { */blob-syms(*) }
+
 	.bstext 0	: { *(.bstext) }
 	.bsdata		: { *(.bsdata) }
 
@@ -45,7 +48,7 @@ SECTIONS
 
 	/DISCARD/ : { *(.note*) }
 
-	. = ALIGN(512);		/* align to sector size */
+	. = ALIGN(4096);		/* align to page size */
 	_setup_size = . - _start;
 	_setup_sects = _setup_size / 512;
 
===================================================================
--- a/arch/i386/kernel/head.S
+++ b/arch/i386/kernel/head.S
@@ -59,6 +59,7 @@ BOOTBITMAP_SIZE = LOW_PAGES / 8
 BOOTBITMAP_SIZE = LOW_PAGES / 8
 ALLOCATOR_SLOP = 4
 
+.globl INIT_MAP_BEYOND_END
 INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE + ALLOCATOR_SLOP)*PAGE_SIZE_asm
 
 /*
===================================================================
--- a/arch/i386/kernel/vmlinux.lds.S
+++ b/arch/i386/kernel/vmlinux.lds.S
@@ -194,6 +194,7 @@ SECTIONS
 	/* This is where the kernel creates the early boot page tables */
 	. = ALIGN(4096);
 	pg0 = . ;
+	__reserved_end = . + INIT_MAP_BEYOND_END - LOAD_OFFSET;
   }
 
   /* Sections to be discarded */

-- 

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[H. Peter Anvin]

Jeremy Fitzhardinge wrote:
> This patch makes the payload of the bzImage file an ELF file.  In
> other words, the bzImage is structured as follows:
>  - boot sector
>  - 16bit setup code
>  - ELF header
>   - decompressor
>   - compressed kernel
> 
> A bootloader may find the start of the ELF file by looking at the
> setup_size entry in the boot params, and using that to find the offset
> of the ELF header.  The ELF Phdrs contain all the mapped memory
> required to decompress and start booting the kernel.
> 
> One slightly complex part of this is that the bzImage boot_params need
> to know about the internal structure of the ELF file, at least to the
> extent of being able to point the core32_start entry at the ELF file's
> entrypoint, so that loaders which use this field will still work.
> 
> Similarly, the ELF header needs to know how big the kernel vmlinux's
> bss segment is, in order to make sure is is mapped properly.
> 
> To handle these two cases, we generate abstracted versions of the
> object files which only contain the symbols we care about (generated
> with objcopy --strip-all --keep-symbol=X), and then include those
> symbol tables with ld -R.

I still believe that we should provide, in effect, vmlinux as a
(compressed) ELF file rather than provide the intermediate stage.  It
would reduce the complexity of testing (all information provided about a
stage have to be both guaranteed to even make sense in the future as
well as be tested to conform to such information) as well as cover a
larger number of environments -- any environment where injecting data
into memory is cheaper than execution is quite unhappy about the current
system.  Such environments include heterogeneous embedded systems (think
a slow CPU on a PCI card where the host CPU has direct access to the
memory on the card) as well as simulators/emulators.

For environments where so is appropriate it would even be possible to
run the setup, invoke the code32_setup hook to do the decompression (and
relocation, if appropriate) in host space.

This makes vmlinux (normally stripped) recoverable from the bzImage file
and so anything that is currently booting vmlinux would be serviced by
this scheme.

	-hpa

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[Jeremy Fitzhardinge]

H. Peter Anvin wrote:
> I still believe that we should provide, in effect, vmlinux as a
> (compressed) ELF file rather than provide the intermediate stage.  It
> would reduce the complexity of testing (all information provided about a
> stage have to be both guaranteed to even make sense in the future as
> well as be tested to conform to such information

I'm not sure I follow you.  Sure, you're right that the Phdr info
contained within the bzImage needs to be tested for correctness.  This
wouldn't normally happen when booting native, but when booting under the
most constrained environment - Xen - it will be tested (and I intend
making the Xen loader as strict as possible).  Of course, it won't help
if the Phdrs are overmap too much, but I don't think that matters too
much, so long as the mappings are not excessively large.

I'm not sure what you mean about "make sense in the future".  If you're
booting the kernel in a new paravirtualized environment, you've
presumably modified the kernel to understand that environment, and
perhaps had to update the boot image format a bit to deal with its
requirements.  I agree that updating the bzImage format may require
retesting in all the other environments, but I think that's probably
true for your scheme as well.

After all, you're assuming that the vmlinux itself provides all
necessary information to be loaded in any environment, which is not
necessarily true (it may need extra ELF notes, for example).  But if
there are any major structural changes needed in the vmlinux, then that
will be equally problematic for both directly using vmlinux and using
ELF-in-bzImage.  So I don't think your argument convincingly sways in
any particular direction.

> ) as well as cover a
> larger number of environments -- any environment where injecting data
> into memory is cheaper than execution is quite unhappy about the current
> system.  Such environments include heterogeneous embedded systems (think
> a slow CPU on a PCI card where the host CPU has direct access to the
> memory on the card) as well as simulators/emulators.
>   

Well, nothing in this scheme precludes the ELF file from being a plain
uncompressed kernel image.  If that's what these environments want, its
easy to provide with a small update to the Makefiles.

> For environments where so is appropriate it would even be possible to
> run the setup, invoke the code32_setup hook to do the decompression (and
> relocation, if appropriate) in host space.
>   

Well, that's what we currently have, and we can't break backwards
compatibility.

> This makes vmlinux (normally stripped) recoverable from the bzImage file
> and so anything that is currently booting vmlinux would be serviced by
> this scheme.
>   

I'm not sure I fully understand the mechanism you're proposing.  You
have the 16-bit setup code, the 32-bit decompressor, and an ELF.gz. Once
the decompressor has extracted the actual ELF file, are you proposing
that it properly parse the ELF file and follow its instuctions to put
the segments in the appropriate places, or are you assuming that the
decompressor can just skip that part and plonk the ELF file where it wants?

In other words, do you see the Phdrs as being descriptive or prescriptive?

    J

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[H. Peter Anvin]

Jeremy Fitzhardinge wrote:
> 
> I'm not sure I fully understand the mechanism you're proposing.  You
> have the 16-bit setup code, the 32-bit decompressor, and an ELF.gz. Once
> the decompressor has extracted the actual ELF file, are you proposing
> that it properly parse the ELF file and follow its instuctions to put
> the segments in the appropriate places, or are you assuming that the
> decompressor can just skip that part and plonk the ELF file where it wants?
> 
> In other words, do you see the Phdrs as being descriptive or prescriptive?
> 

I was thinking prescriptive, having the decompressor read the output
stream and interpret it as ELF.  I guess a descriptive approach could be
made to work, too (I haven't really thought about that avenue of
approach), but the prescriptive model seems more powerful, at least to me.

	-hpa

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[Jeremy Fitzhardinge]

H. Peter Anvin wrote:
> I was thinking prescriptive, having the decompressor read the output
> stream and interpret it as ELF.  I guess a descriptive approach could be
> made to work, too (I haven't really thought about that avenue of
> approach), but the prescriptive model seems more powerful, at least to me.

Certainly, but much harder to implement.  The ELF parser needs to be
prepared to move itself around to get out of the way of the ELF file. 
It's a fairly large change from how it works now.

I was thinking of making the ELF file entirely descriptive, since its
just a set of ELF headers inserted into the existing bzImage structure,
and it still relies on the bzImage being build properly in the first place.

    J

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[H. Peter Anvin]

Jeremy Fitzhardinge wrote:
> 
> Certainly, but much harder to implement.  The ELF parser needs to be
> prepared to move itself around to get out of the way of the ELF file. 
> It's a fairly large change from how it works now.
> 

It doesn't if we simply declare that a certain chunk of memory is
available to it, for the case where it runs in the native configuration.
Since it doesn't have to support *any* ELF file, just the kernel one,
that's an option.

On the other hand, I guess with the decompressor/ELF parser being PIC,
one would simply look for the highest used address, and relocate itself
above that point.  It's not really all that different from what the
decompressor does today, except that it knows the address a priori.

> I was thinking of making the ELF file entirely descriptive, since its
> just a set of ELF headers inserted into the existing bzImage structure,
> and it still relies on the bzImage being build properly in the first place.

Again, it's an option.  The downside is that you don't get the automatic
test coverage of having it be exercised as often as possible.

	-hpa

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[Jeremy Fitzhardinge]

H. Peter Anvin wrote:
> It doesn't if we simply declare that a certain chunk of memory is
> available to it, for the case where it runs in the native configuration.
> Since it doesn't have to support *any* ELF file, just the kernel one,
> that's an option.
>   

I suppose.  But given that its always built at the same time as - and
linked to - the kernel itself, it can have private knowledge about the
kernel.

> On the other hand, I guess with the decompressor/ELF parser being PIC,
> one would simply look for the highest used address, and relocate itself
> above that point.  It's not really all that different from what the
> decompressor does today, except that it knows the address a priori.
>   

Yes, it would have to decompress the ELF file into a temp buffer, and
then rearrange itself and the decompressed ELF file to make space for
the ELF file's final location.  Seems a bit more complex because it has
to be done in the middle of execution rather that at start of day.  But
perhaps that doesn't matter very much.

>> I was thinking of making the ELF file entirely descriptive, since its
>> just a set of ELF headers inserted into the existing bzImage structure,
>> and it still relies on the bzImage being build properly in the first place.
>>     
>
> Again, it's an option.  The downside is that you don't get the automatic
> test coverage of having it be exercised as often as possible.

I don't follow your argument at all.

I'm proposing the kernel take the same code path regardless of how its
booted, with the only two variations:

   1. boot all the way up from 16-bit mode, or
   2. start directly in 32-bit mode

which is essentially the current situation (setup vs code32_start).  All
I'm adding is a bit more metadata for the domain builder to work with. 
The code will get exercised on every boot in every environment, and the
metadata will be tested by whichever environment cares about it.

You're proposing that we add a third booting variation, where the
bootloader takes on the responsibility for decompressing and loading the
kernel's ELF image.  In addition, you're proposing changing the existing
32-bit portion of the boot to perform the same job as the third method,
but in a way which is not reusable by a paravirtual domain builder. 
This means that the boot path is unique for each boot environment, and
so will overall get less coverage.

Given that one axis of the test matrix - "number of subarchtectures" -
is the same in both cases, and the other axis - "number of ways of
booting" - is larger in your proposal, it seems to me that your's has
the higher testing burden.

Anyway, I added an extra pointer in the boot_params so that you can
implement it that way if you really want (no real reason you can have
ELF within ELF within bzImage, but it starts to look a bit
engineering-by-compromise at that point).  It isn't, however, the
approach I want to take with Xen.

    J

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[Vivek Goyal]

On Wed, Jun 06, 2007 at 05:42:35PM -0700, H. Peter Anvin wrote:
> Jeremy Fitzhardinge wrote:
> > 
> > Certainly, but much harder to implement.  The ELF parser needs to be
> > prepared to move itself around to get out of the way of the ELF file. 
> > It's a fairly large change from how it works now.
> > 
> 
> It doesn't if we simply declare that a certain chunk of memory is
> available to it, for the case where it runs in the native configuration.
> Since it doesn't have to support *any* ELF file, just the kernel one,
> that's an option.
> 
> On the other hand, I guess with the decompressor/ELF parser being PIC,
> one would simply look for the highest used address, and relocate itself
> above that point.  It's not really all that different from what the
> decompressor does today, except that it knows the address a priori.
> 

One would not know highest used address until ELF headers have been 
parsed. May be it is two step movement. First decompress ELF.gz and 
ELF parser can be at the end of decompressed data. Then it can parse
the ELF headers and move itself out of the ELF header destination memory
and then load the elf segments at appropriate place.

One will have to be little careful while moving ELF parser or while
decompressing the file to a temporary buffer so that we don't stomp over
any other data loaded by boot-loader (like kexec does) or we don't go beyond
the memory bounds which might have been created in the case of using kdump.

Thanks
Vivek

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[H. Peter Anvin]

Vivek Goyal wrote:
> 
> One would not know highest used address until ELF headers have been 
> parsed. May be it is two step movement. First decompress ELF.gz and 
> ELF parser can be at the end of decompressed data. Then it can parse
> the ELF headers and move itself out of the ELF header destination memory
> and then load the elf segments at appropriate place.
> 
> One will have to be little careful while moving ELF parser or while
> decompressing the file to a temporary buffer so that we don't stomp over
> any other data loaded by boot-loader (like kexec does) or we don't go beyond
> the memory bounds which might have been created in the case of using kdump.
> 

The easiest is probably to decode the ELF headers (which can be done in
O(1) space), relocate, reset the decompressor and restart.

Relocation is currently done in the decompressor, but it could also be
done at the kernel entrypoint, as long as the kernel entrypoint code is
all PIC.

	-hpa

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[Rob Landley]

On Wednesday 06 June 2007 7:41 pm, H. Peter Anvin wrote:
> This makes vmlinux (normally stripped) recoverable from the bzImage file
> and so anything that is currently booting vmlinux would be serviced by
> this scheme.

Would this make it sane to strip the initramfs image out of vmlinux with 
objdump and replace it with another one, or are there offsets resolved during 
the build that stop that for vmlinux?

Rob
-- 
The Google cluster became self-aware at 2:14am EDT August 29, 2007...

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[H. Peter Anvin]

Rob Landley wrote:
> On Wednesday 06 June 2007 7:41 pm, H. Peter Anvin wrote:
>> This makes vmlinux (normally stripped) recoverable from the bzImage file
>> and so anything that is currently booting vmlinux would be serviced by
>> this scheme.
> 
> Would this make it sane to strip the initramfs image out of vmlinux with 
> objdump and replace it with another one, or are there offsets resolved during 
> the build that stop that for vmlinux?
> 

There probably are offsets resolved during the build.  However, that
wouldn't be all that hard to fix.  Still, one can argue whether or not
it is sane under any definition to do this kind of unpacking-repacking
of ELF files.

	-hpa

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[Rob Landley]

On Wednesday 06 June 2007 9:54 pm, H. Peter Anvin wrote:
> Rob Landley wrote:
> > On Wednesday 06 June 2007 7:41 pm, H. Peter Anvin wrote:
> >> This makes vmlinux (normally stripped) recoverable from the bzImage file
> >> and so anything that is currently booting vmlinux would be serviced by
> >> this scheme.
> > 
> > Would this make it sane to strip the initramfs image out of vmlinux with 
> > objdump and replace it with another one, or are there offsets resolved 
during 
> > the build that stop that for vmlinux?
> > 
> 
> There probably are offsets resolved during the build.  However, that
> wouldn't be all that hard to fix.  Still, one can argue whether or not
> it is sane under any definition to do this kind of unpacking-repacking
> of ELF files.

Er, make that objcopy, not objdump.

Sane, maybe not.  Something people want to do (and under the mistaken 
assumption I know more about initramfs then they do, have asked me how), yes.  
It always boils down to "do you have a vmlinux image lying around?  Doing 
this with a bzImage _is_ brain surgery", and has yet to get beyond that 
question.  I had about half of a script worked out for this, once...

You can also supply an external initramfs image through the initrd mechanism, 
but this is unpleasant to do with some bootloaders (or lack of bootloaders).  
Plus it doesn't remove the old one, and wasting space makes embedded 
developers itch.

Rob
-- 
The Google cluster became self-aware at 2:14am EDT August 29, 2007...

Re: [PATCH RFC 6/7] i386: make the bzImage payload an ELF file

[H. Peter Anvin]

Rob Landley wrote:
> 
> Er, make that objcopy, not objdump.
> 
> Sane, maybe not.  Something people want to do (and under the mistaken 
> assumption I know more about initramfs then they do, have asked me how), yes.  
> It always boils down to "do you have a vmlinux image lying around?  Doing 
> this with a bzImage _is_ brain surgery", and has yet to get beyond that 
> question.  I had about half of a script worked out for this, once...
> 

If it can be done today on a vmlinux then it can be done the same way
with the mechanism I have proposed.  Period, full stop.

> You can also supply an external initramfs image through the initrd mechanism, 
> but this is unpleasant to do with some bootloaders (or lack of bootloaders).  
> Plus it doesn't remove the old one, and wasting space makes embedded 
> developers itch.

In thory one could create an extended bzImage format which could handle
a concatenated, and easily replaceable, initrd, but if it's done on
vmlinux today it would make a *lot* more sense to have it be done on the
vmlinux and nothing else.

	-hpa

[PATCH RFC 7/7] i386: paravirt boot sequence

[Jeremy Fitzhardinge]

[-- Attachment #1: i386-paravirt-bootup.patch --]
[-- Type: text/plain, Size: 4226 bytes --]

This patch uses the updated boot protocol to do paravirtualized boot.
If the boot version is >= 2.07, then it will do two things:

 1. Check the bootparams loadflags to see if we should reload the
    segment registers and clear interrupts.  This is appropriate
    for normal native boot and some paravirtualized environments, but
    inappropraite for others.

 2. Check the hardware architecture, and dispatch to the appropriate
    kernel entrypoint.  If the bootloader doesn't set this, then we
    simply do the normal boot sequence.

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

---
 arch/i386/boot/header.S |    9 ++++++++-
 arch/i386/kernel/head.S |   47 +++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 51 insertions(+), 5 deletions(-)

===================================================================
--- a/arch/i386/boot/header.S
+++ b/arch/i386/boot/header.S
@@ -119,7 +119,7 @@ 1:
 	# Part 2 of the header, from the old setup.S
 
 		.ascii	"HdrS"		# header signature
-		.word	0x0206		# header version number (>= 0x0105)
+		.word	0x0207		# header version number (>= 0x0105)
 					# or else old loadlin-1.5 will fail)
 		.globl realmode_swtch
 realmode_swtch:	.word	0, 0		# default_switch, SETUPSEG
@@ -209,6 +209,13 @@ cmdline_size:   .long   COMMAND_LINE_SIZ
                                                 #added with boot protocol
                                                 #version 2.06
 
+hardware_subarch:	.long 0			# subarchitecture, added with 2.07
+						# default to 0 for normal x86 PC
+
+hardware_subarch_data:	.quad 0
+
+kernel_payload:		.long blob_payload	# raw kernel data
+
 # End of setup header #####################################################
 
 	.section ".inittext", "ax"
===================================================================
--- a/arch/i386/kernel/head.S
+++ b/arch/i386/kernel/head.S
@@ -71,28 +71,37 @@ INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + 
  */
 .section .text.head,"ax",@progbits
 ENTRY(startup_32)
+	/* check to see if KEEP_SEGMENTS flag is meaningful */
+	cmpw $0x207, BP_version(%esi)
+	jb 1f
+
+	/* test KEEP_SEGMENTS flag to see if the bootloader is asking
+		us to not reload segments */
+	testb $(1<<6), BP_loadflags(%esi)
+	jnz 2f
 
 /*
  * Set segments to known values.
  */
-	cld
-	lgdt boot_gdt_descr - __PAGE_OFFSET
+1:	lgdt boot_gdt_descr - __PAGE_OFFSET
 	movl $(__BOOT_DS),%eax
 	movl %eax,%ds
 	movl %eax,%es
 	movl %eax,%fs
 	movl %eax,%gs
+2:
 
 /*
  * Clear BSS first so that there are no surprises...
- * No need to cld as DF is already clear from cld above...
- */
+ */
+	cld
 	xorl %eax,%eax
 	movl $__bss_start - __PAGE_OFFSET,%edi
 	movl $__bss_stop - __PAGE_OFFSET,%ecx
 	subl %edi,%ecx
 	shrl $2,%ecx
 	rep ; stosl
+
 /*
  * Copy bootup parameters out of the way.
  * Note: %esi still has the pointer to the real-mode data.
@@ -120,6 +129,35 @@ 2:
 	movsl
 1:
 
+#ifdef CONFIG_PARAVIRT
+	cmpw $0x207, (boot_params + BP_version - __PAGE_OFFSET)
+	jb default_entry
+
+	/* Paravirt-compatible boot parameters.  Look to see what architecture
+		we're booting under. */
+	movl (boot_params + BP_hardware_subarch - __PAGE_OFFSET), %eax
+	cmpl $num_subarch_entries, %eax
+	jae bad_subarch
+
+	movl subarch_entries - __PAGE_OFFSET(,%eax,4), %eax
+	subl $__PAGE_OFFSET, %eax
+	jmp *%eax
+
+bad_subarch:
+WEAK(lguest_entry)
+WEAK(xen_entry)
+	/* Unknown implementation; there's really
+	   nothing we can do at this point. */
+	ud2a
+.data
+subarch_entries:
+	.long default_entry		/* normal x86/PC */
+	.long lguest_entry		/* lguest hypervisor */
+	.long xen_entry			/* Xen hypervisor */
+num_subarch_entries = (. - subarch_entries) / 4
+.previous
+#endif /* CONFIG_PARAVIRT */
+
 /*
  * Initialize page tables.  This creates a PDE and a set of page
  * tables, which are located immediately beyond _end.  The variable
@@ -132,6 +170,7 @@ 1:
  */
 page_pde_offset = (__PAGE_OFFSET >> 20);
 
+default_entry:
 	movl $(pg0 - __PAGE_OFFSET), %edi
 	movl $(swapper_pg_dir - __PAGE_OFFSET), %edx
 	movl $0x007, %eax			/* 0x007 = PRESENT+RW+USER */

--