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Message-Id: <1203013792.30565.21.camel@cthulhu.hellion.org.uk>
Date: Thu, 14 Feb 2008 18:29:52 +0000
From: Ian Campbell <ijc@...lion.org.uk>
To: Mark McLoughlin <markmc@...hat.com>
Cc: linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv3 1/3] x86: use ELF format in compressed images.
On Thu, 2008-02-14 at 17:01 +0000, Ian Campbell wrote:
>
> > > +Field name: compressed_payload_offset
> > > +Type: read
> > > +Offset/size: 0x248/4
> > > +Protocol: 2.08+
> > > +
> > > + If non-zero then this field contains the offset from the end of
> the
> > > + real-mode code to the compressed payload. The compression
> format
> > > + should be determined using the standard magic number, currently
> only
> > > + gzip is used.
> >
> > Should probably mention that the payload format is expected to
> be ELF.
>
> Agreed. Probably the same deal as the compression format, i.e. use the
> magic number but only ELF is possible today (even less likely to
> change than the compression format I guess...).
Updated with a note about ELF format payload.
I've also changed the fields to just payload_{offset,length} and
adjusted the description to allow for the possibility of non-compressed
ELF payloads. I don't have a use for it myself but I can see how it
might be useful (embedded systems?) so it seems reasonable not to rule
it out. ELF-in-gzip and plain ELF can both be identified by magic
numbers.
Ian.
---
>>From 544c003d4067d895556180fc11a951e211202d0d Mon Sep 17 00:00:00 2001
From: Ian Campbell <ijc@...lion.org.uk>
Date: Thu, 14 Feb 2008 18:29:01 +0000
Subject: [PATCH] x86: use ELF format in compressed images.
This allows other boot loaders such as the Xen domain builder the
opportunity to extract the ELF file.
Signed-off-by: Ian Campbell <ijc@...lion.org.uk>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Jeremy Fitzhardinge <jeremy@...p.org>
Cc: virtualization@...ts.linux-foundation.org
---
Documentation/i386/boot.txt | 20 +++++++++++++
arch/x86/boot/Makefile | 14 +++++++++
arch/x86/boot/compressed/Makefile | 2 +-
arch/x86/boot/compressed/misc.c | 56 +++++++++++++++++++++++++++++++++++++
arch/x86/boot/header.S | 4 ++
5 files changed, 95 insertions(+), 1 deletions(-)
diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt
index fc49b79..f2e54e5 100644
--- a/Documentation/i386/boot.txt
+++ b/Documentation/i386/boot.txt
@@ -170,6 +170,8 @@ Offset Proto Name Meaning
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 2.08+ payload_offset Offset of kernel payload
+024C/4 2.08+ payload_length Length of kernel payload
(1) For backwards compatibility, if the setup_sects field contains 0, the
real value is 4.
@@ -512,6 +514,24 @@ Protocol: 2.07+
A pointer to data that is specific to hardware subarch
+Field name: payload_offset
+Type: read
+Offset/size: 0x248/4
+Protocol: 2.08+
+
+ If non-zero then this field contains the offset from the end of the
+ real-mode code to the payload.
+
+ The payload may be compressed. The format of both the compressed and
+ uncompressed data should be determined using the standard magic
+ numbers. Currently only gzip compressed ELF is used.
+
+Field name: payload_length
+Type: read
+Offset/size: 0x24c/4
+Protocol: 2.08+
+
+ The length of the payload.
**** THE KERNEL COMMAND LINE
diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index f88458e..9695aff 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -94,6 +94,20 @@ $(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE
SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))
+sed-offsets := -e 's/^00*/0/' \
+ -e 's/^\([0-9a-fA-F]*\) . \(input_data\|input_data_end\)$$/\#define \2 0x\1/p'
+
+quiet_cmd_offsets = OFFSETS $@
+ cmd_offsets = $(NM) $< | sed -n $(sed-offsets) > $@
+
+$(obj)/offsets.h: $(obj)/compressed/vmlinux FORCE
+ $(call if_changed,offsets)
+
+targets += offsets.h
+
+AFLAGS_header.o += -I$(obj)
+$(obj)/header.o: $(obj)/offsets.h
+
LDFLAGS_setup.elf := -T
$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
$(call if_changed,ld)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index d2b9f3b..92fdd35 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -22,7 +22,7 @@ $(obj)/vmlinux: $(src)/vmlinux_$(BITS).lds $(obj)/head_$(BITS).o $(obj)/misc.o $
$(call if_changed,ld)
@:
-OBJCOPYFLAGS_vmlinux.bin := -O binary -R .note -R .comment -S
+OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
$(obj)/vmlinux.bin: vmlinux FORCE
$(call if_changed,objcopy)
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 8182e32..69aec2f 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -15,6 +15,10 @@
* we just keep it from happening
*/
#undef CONFIG_PARAVIRT
+#ifdef CONFIG_X86_32
+#define _ASM_DESC_H_ 1
+#endif
+
#ifdef CONFIG_X86_64
#define _LINUX_STRING_H_ 1
#define __LINUX_BITMAP_H 1
@@ -22,6 +26,7 @@
#include <linux/linkage.h>
#include <linux/screen_info.h>
+#include <linux/elf.h>
#include <asm/io.h>
#include <asm/page.h>
#include <asm/boot.h>
@@ -365,6 +370,56 @@ static void error(char *x)
asm("hlt");
}
+static void parse_elf(void *output)
+{
+#ifdef CONFIG_X86_64
+ Elf64_Ehdr ehdr;
+ Elf64_Phdr *phdrs, *phdr;
+#else
+ Elf32_Ehdr ehdr;
+ Elf32_Phdr *phdrs, *phdr;
+#endif
+ void *dest;
+ int i;
+
+ memcpy(&ehdr, output, sizeof(ehdr));
+ if(ehdr.e_ident[EI_MAG0] != ELFMAG0 ||
+ ehdr.e_ident[EI_MAG1] != ELFMAG1 ||
+ ehdr.e_ident[EI_MAG2] != ELFMAG2 ||
+ ehdr.e_ident[EI_MAG3] != ELFMAG3)
+ {
+ error("Kernel is not a valid ELF file");
+ return;
+ }
+
+ putstr("Parsing ELF... ");
+
+ phdrs = malloc(sizeof(*phdrs) * ehdr.e_phnum);
+ if (!phdrs)
+ error("Failed to allocate space for phdrs");
+
+ memcpy(phdrs, output + ehdr.e_phoff, sizeof(*phdrs) * ehdr.e_phnum);
+
+ for (i=0; i<ehdr.e_phnum; i++) {
+ phdr = &phdrs[i];
+
+ switch (phdr->p_type) {
+ case PT_LOAD:
+#ifdef CONFIG_RELOCATABLE
+ dest = output;
+ dest += (phdr->p_paddr - LOAD_PHYSICAL_ADDR);
+#else
+ dest = (void*)(phdr->p_paddr);
+#endif
+ memcpy(dest,
+ output + phdr->p_offset,
+ phdr->p_filesz);
+ break;
+ default: /* Ignore other PT_* */ break;
+ }
+ }
+}
+
asmlinkage void decompress_kernel(void *rmode, memptr heap,
uch *input_data, unsigned long input_len,
uch *output)
@@ -408,6 +463,7 @@ asmlinkage void decompress_kernel(void *rmode, memptr heap,
makecrc();
putstr("\nDecompressing Linux... ");
gunzip();
+ parse_elf(output);
putstr("done.\nBooting the kernel.\n");
return;
}
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 64ad901..4085616 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -22,6 +22,7 @@
#include <asm/page.h>
#include <asm/setup.h>
#include "boot.h"
+#include "offsets.h"
SETUPSECTS = 4 /* default nr of setup-sectors */
BOOTSEG = 0x07C0 /* original address of boot-sector */
@@ -223,6 +224,9 @@ hardware_subarch: .long 0 # subarchitecture, added with 2.07
hardware_subarch_data: .quad 0
+payload_offset: .long input_data
+payload_length: .long input_data_end-input_data
+
# End of setup header #####################################################
.section ".inittext", "ax"
--
1.5.4
--
Ian Campbell
The moss on the tree does not fear the talons of the hawk.
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