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SubjectRe: PATCH/RFC: bzImage payload as compressed ELF file.
Ian Campbell wrote:
> I'm mainly interested in something along these lines to allow the Xen
> bootloader to load a bzImage so that distros don't have to maintain two
> kernel packages with the same basic bits in different file formats, I
> think it would probably be of use to the kexec and/or lguest folks too.
>
> The patch boots on native 32 and 64 bit x86. I haven't done the matching
> Xen domain builder work but the attached bzexplode.c is a trivial/ugly
> (don't judge me based on it ;-)) test app which extracts the payload,
> which I have been able to boot as a 32 bit Xen domU, as you'd expect.
>

I've got a bzImage-loading domain builder patch somewhere. It's based
on my version of what you've done here, which isn't very different.

> The payload is simply the stripped and compressed toplevel vmlinux file.
> I assume that ELF program headers will be ordered by physical address
> within the ELF file since this (and the general simplicity of the kernel
> ELF layout) makes the ELF "parser" pretty trivial. I think the
> assumption is safe because for the kernel paddr=vaddr-offset and the ELF
> spec says (in book I chapter 2 "Program Header"):
> Loadable segment entries in the program header table appear in
> ascending order, sorted on the p_vaddr member.
> Slightly less obvious is if the data within the ELF file is in the same
> order as the program headers. I think the kernel is constrained enough
> that we can guarantee this.
>

The problem I ran into is that 32-bit boot loaders expect to be able to
load the payload portion of the bzImage and simply jmp 0x100000, which
would start executing the ELF header. Someone (Vivek Goyal?) did a
neat/bizarre/awful hack which made the ELF header itself executable,
which wasn't something I felt should live.

> What would be the preferred way of allowing bootloaders/domain builders
> to find the compressed payload? Tacking the offset from the end onto the
> end as I have done for the moment seems pretty skanky...
>

The header format is extensible, so you just up the bootloader revision
and put the appropriate extra members.

J

> Ian.
>
> x86: switch compressed payload to ELF format.
>
> This allows other boot loaders such as the Xen domain builder the
> opportunity to extract the ELF file.
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index b7541a4..69d740b 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -90,7 +90,6 @@ KBUILD_AFLAGS += $(cfi) $(cfi-sigframe)
> KBUILD_CFLAGS += $(cfi) $(cfi-sigframe)
>
> LDFLAGS := -m elf_$(UTS_MACHINE)
> -OBJCOPYFLAGS := -O binary -R .note -R .comment -S
>
> # Speed up the build
> KBUILD_CFLAGS += -pipe
> diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> index 349b81a..23fddca 100644
> --- a/arch/x86/boot/Makefile
> +++ b/arch/x86/boot/Makefile
> @@ -80,6 +80,7 @@ $(obj)/zImage $(obj)/bzImage: $(obj)/setup.bin \
> $(call if_changed,image)
> @echo 'Kernel: $@ is ready' ' (#'`cat .version`')'
>
> +$(obj)/vmlinux.bin: OBJCOPYFLAGS := -O binary -R .note -R .comment -S
> $(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE
> $(call if_changed,objcopy)
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index fe24cea..aedea1c 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -22,6 +22,7 @@ $(obj)/vmlinux: $(src)/vmlinux_$(BITS).lds $(obj)/head_$(BITS).o $(obj)/misc.o $
> $(call if_changed,ld)
> @:
>
> +$(obj)/vmlinux.bin: OBJCOPYFLAGS := -R .comment --strip-all
> $(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..2eb8a8b 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 +370,71 @@ 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
> + 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)
> + {
> + putstr("Not ELF... ");
> + 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_NULL:
> + putstr("\nIgnoring PT_NULL PHDR... ");
> + break;
> + case PT_LOAD:
> + putstr("\nProcessing PT_LOAD PHDR... ");
> + memcpy((void*)phdr->p_paddr,
> + output + phdr->p_offset,
> + phdr->p_filesz);
> + break;
> + case PT_DYNAMIC:
> + putstr("\nIgnoring PT_DYNAMIC PHDR... ");
> + break;
> + case PT_INTERP:
> + putstr("\nIgnoring PT_INTERP PHDR... ");
> + break;
> + case PT_NOTE:
> + putstr("\nIgnoring PT_NOTE PHDR... ");
> + break;
> + case PT_SHLIB:
> + putstr("\nIgnoring PT_SHLIB PHDR... ");
> + break;
> + case PT_PHDR:
> + putstr("\nIgnoring PT_PHDR PHDR... ");
> + break;
> + case PT_TLS:
> + putstr("\nIgnoring PT_TLS PHDR... ");
> + break;
> + default:
> + putstr("\nIgnoring unknown PHDR... ");
> + }
> + }
> +}
> +
> asmlinkage void decompress_kernel(void *rmode, memptr heap,
> uch *input_data, unsigned long input_len,
> uch *output)
> @@ -408,6 +478,7 @@ 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/compressed/vmlinux_32.lds b/arch/x86/boot/compressed/vmlinux_32.lds
> index bb3c483..1eb2a02 100644
> --- a/arch/x86/boot/compressed/vmlinux_32.lds
> +++ b/arch/x86/boot/compressed/vmlinux_32.lds
> @@ -40,4 +40,8 @@ SECTIONS
> *(COMMON)
> _end = . ;
> }
> + .data.trailer : {
> + LONG(. - input_data + 8) payload_offset = .;
> + LONG(input_data_end - input_data) payload_length = .;
> + }
> }
> diff --git a/arch/x86/boot/compressed/vmlinux_64.lds b/arch/x86/boot/compressed/vmlinux_64.lds
> index f6e5b44..dcb9773 100644
> --- a/arch/x86/boot/compressed/vmlinux_64.lds
> +++ b/arch/x86/boot/compressed/vmlinux_64.lds
> @@ -45,4 +45,8 @@ SECTIONS
> . = . + 4096 * 6;
> _heap = .;
> }
> + .data.trailer : {
> + LONG(. - input_data + 8) payload_offset = .;
> + LONG(input_data_end - input_data) payload_length = .;
> + }
> }
>
>

diff -r cbb2280c9959 tools/libxc/Makefile
--- a/tools/libxc/Makefile Mon Jun 18 18:02:30 2007 -0700
+++ b/tools/libxc/Makefile Tue Jun 19 02:03:13 2007 -0700
@@ -47,6 +47,7 @@ GUEST_SRCS-y += $(LIBELF_SRCS)
# new domain builder
GUEST_SRCS-y += xc_dom_core.c xc_dom_boot.c
GUEST_SRCS-y += xc_dom_elfloader.c
+GUEST_SRCS-y += xc_dom_bzimageloader.c
GUEST_SRCS-y += xc_dom_binloader.c
GUEST_SRCS-y += xc_dom_compat_linux.c

diff -r cbb2280c9959 tools/libxc/bootparam.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/tools/libxc/bootparam.h Tue Jun 19 02:03:13 2007 -0700
@@ -0,0 +1,53 @@
+#ifndef _ASM_BOOTPARAM_H
+#define _ASM_BOOTPARAM_H
+
+#include <stdint.h>
+
+#define HDR_MAGIC "HdrS"
+#define HDR_MAGIC_SZ 4
+
+struct setup_header {
+ uint8_t setup_sects;
+ uint16_t root_flags;
+ uint32_t syssize;
+ uint16_t ram_size;
+ uint16_t vid_mode;
+ uint16_t root_dev;
+ uint16_t boot_flag;
+ uint16_t jump;
+ uint32_t header;
+ uint16_t version;
+#define VERSION(h,l) (((h)<<8) | (l))
+ uint32_t realmode_swtch;
+ uint16_t start_sys;
+ uint16_t kernel_version;
+ uint8_t type_of_loader;
+ uint8_t loadflags;
+#define LOADED_HIGH (1<<0)
+#define KEEP_SEGMENTS (1<<6)
+#define CAN_USE_HEAP (1<<7)
+ uint16_t setup_move_size;
+ uint32_t code32_start;
+ uint32_t ramdisk_image;
+ uint32_t ramdisk_size;
+ uint32_t bootsect_kludge;
+ uint16_t heap_end_ptr;
+ uint16_t _pad1;
+ uint32_t cmd_line_ptr;
+ uint32_t initrd_addr_max;
+ uint32_t kernel_alignment;
+ uint8_t relocatable_kernel;
+ uint8_t _pad2[3];
+ uint32_t cmdline_size;
+ uint32_t hardware_subarch;
+ uint64_t hardware_subarch_data;
+} __attribute__((packed));
+
+/* The so-called "zeropage" */
+struct boot_params {
+ uint8_t _pad0[0x1f1]; /* skip uninteresting stuff */
+ struct setup_header hdr;/* setup header */ /* 0x1f1 */
+ uint8_t _pad7[0x1000-0x1f1-sizeof(struct setup_header)];
+} __attribute__((packed));
+
+#endif /* _ASM_BOOTPARAM_H */
diff -r cbb2280c9959 tools/libxc/xc_dom.h
--- a/tools/libxc/xc_dom.h Mon Jun 18 18:02:30 2007 -0700
+++ b/tools/libxc/xc_dom.h Tue Jun 19 02:03:13 2007 -0700
@@ -55,6 +55,7 @@ struct xc_dom_image {
xen_pfn_t xenstore_pfn;
xen_pfn_t shared_info_pfn;
xen_pfn_t bootstack_pfn;
+ xen_pfn_t bootparams_pfn;
xen_vaddr_t virt_alloc_end;
xen_vaddr_t bsd_symtab_start;

@@ -254,6 +255,8 @@ static inline xen_pfn_t xc_dom_p2m_guest
return dom->p2m_host[pfn];
}

+char *xc_dom_guest_type(struct xc_dom_image *dom,
+ struct elf_binary *elf);
/* --- arch bits --------------------------------------------------- */

int arch_setup_meminit(struct xc_dom_image *dom);
diff -r cbb2280c9959 tools/libxc/xc_dom_bzimageloader.c
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/tools/libxc/xc_dom_bzimageloader.c Tue Jun 19 02:03:13 2007 -0700
@@ -0,0 +1,164 @@
+/*
+ * Xen domain builder -- bzImage bits
+ *
+ * Parse and load bzImage kernel images.
+ *
+ * This relies on version 2.07 of the boot protocol, which an ELF file
+ * embedded in the bzImage. The loader extracts the boot_params from
+ * the bzImage and updates it appropriately, then loads and runs the
+ * self-extracting kernel ELF file.
+ *
+ * This code is licenced under the GPL.
+ * written 2006 by Gerd Hoffmann <kraxel@suse.de>.
+ * written 2007 by Jeremy Fitzhardinge <jeremy@xensource.com>
+ *
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <inttypes.h>
+
+#include "xg_private.h"
+#include "xc_dom.h"
+#include "bootparam.h"
+
+#define XEN_VER "xen-3.0"
+
+static unsigned elf_offset(struct boot_params *params)
+{
+ return (params->hdr.setup_sects + 1) * 512;
+}
+
+static int check_bzimage_kernel(struct xc_dom_image *dom, int verbose)
+{
+ struct boot_params *params;
+ const char *elf;
+
+ if ( dom->kernel_blob == NULL || dom->kernel_size < 512*8)
+ {
+ if ( verbose )
+ xc_dom_panic(XC_INTERNAL_ERROR, "%s: no kernel image loaded\n",
+ __FUNCTION__);
+ return -EINVAL;
+ }
+
+ params = dom->kernel_blob;
+
+ if ( memcmp(&params->hdr.header, HDR_MAGIC, HDR_MAGIC_SZ) != 0 )
+ {
+ if ( verbose )
+ xc_dom_panic(XC_INVALID_KERNEL, "%s: kernel is not a bzImage\n",
+ __FUNCTION__);
+ return -EINVAL;
+ }
+
+ if ( params->hdr.version < VERSION(2,07) )
+ {
+ if ( verbose )
+ xc_dom_panic(XC_INVALID_KERNEL, "%s: boot protocol too old (%04x)\n",
+ __FUNCTION__, params->hdr.version);
+ return -EINVAL;
+ }
+
+ elf = dom->kernel_blob + elf_offset(params);
+ if ( !elf_is_elfbinary(elf) )
+ {
+ if ( verbose )
+ xc_dom_panic(XC_INVALID_KERNEL, "%s: bzImage does not contain ELF image\n",
+ __FUNCTION__);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static int xc_dom_probe_bzimage_kernel(struct xc_dom_image *dom)
+{
+ return check_bzimage_kernel(dom, 0);
+}
+
+static int xc_dom_parse_bzimage_kernel(struct xc_dom_image *dom)
+{
+ int rc;
+ struct boot_params *params;
+ struct elf_binary *elf;
+ unsigned offset;
+
+ rc = check_bzimage_kernel(dom, 1);
+ if ( rc != 0 )
+ return rc;
+
+ params = dom->kernel_blob;
+ offset = elf_offset(params);
+
+ elf = xc_dom_malloc(dom, sizeof(*elf));
+ dom->private_loader = elf;
+
+ rc = elf_init(elf, dom->kernel_blob + offset, dom->kernel_size - offset);
+ if ( xc_dom_logfile )
+ elf_set_logfile(elf, xc_dom_logfile, 1);
+ if ( rc != 0 )
+ {
+ xc_dom_panic(XC_INVALID_KERNEL, "%s: corrupted ELF image\n",
+ __FUNCTION__);
+ return rc;
+ }
+
+ /* parse binary and get xen meta info */
+ elf_parse_binary(elf);
+ if ( (rc = elf_xen_parse(elf, &dom->parms)) != 0 )
+ return rc;
+
+ /* find kernel segment */
+ dom->kernel_seg.vstart = dom->parms.virt_kstart;
+ dom->kernel_seg.vend = dom->parms.virt_kend;
+
+ dom->guest_type = xc_dom_guest_type(dom, elf);
+ xc_dom_printf("%s: %s: 0x%" PRIx64 " -> 0x%" PRIx64 "\n",
+ __FUNCTION__, dom->guest_type,
+ dom->kernel_seg.vstart, dom->kernel_seg.vend);
+ return 0;
+}
+
+static int xc_dom_load_bzimage_kernel(struct xc_dom_image *dom)
+{
+ struct elf_binary *elf = dom->private_loader;
+ xen_pfn_t bootparams_pfn;
+ struct boot_params *bzparams, *bootparams;
+
+ bzparams = dom->kernel_blob;
+
+ elf->dest = xc_dom_seg_to_ptr(dom, &dom->kernel_seg);
+ elf_load_binary(elf);
+
+ bootparams_pfn = xc_dom_alloc_page(dom, "bootparams");
+ bootparams = xc_dom_pfn_to_ptr(dom, bootparams_pfn, 1);
+ memset(bootparams, 0, sizeof(*bootparams));
+
+ memcpy(&bootparams->hdr, &bzparams->hdr, sizeof(bootparams->hdr));
+
+ dom->bootparams_pfn = bootparams_pfn;
+
+ return 0;
+}
+
+static struct xc_dom_loader bzimage_loader = {
+ .name = "bzImage",
+ .probe = xc_dom_probe_bzimage_kernel,
+ .parser = xc_dom_parse_bzimage_kernel,
+ .loader = xc_dom_load_bzimage_kernel,
+};
+
+static void __init register_loader(void)
+{
+ xc_dom_register_loader(&bzimage_loader);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-set-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff -r cbb2280c9959 tools/libxc/xc_dom_elfloader.c
--- a/tools/libxc/xc_dom_elfloader.c Mon Jun 18 18:02:30 2007 -0700
+++ b/tools/libxc/xc_dom_elfloader.c Tue Jun 19 02:03:13 2007 -0700
@@ -18,8 +18,8 @@

/* ------------------------------------------------------------------------ */

-static char *xc_dom_guest_type(struct xc_dom_image *dom,
- struct elf_binary *elf)
+char *xc_dom_guest_type(struct xc_dom_image *dom,
+ struct elf_binary *elf)
{
uint64_t machine = elf_uval(elf, elf->ehdr, e_machine);

diff -r cbb2280c9959 tools/libxc/xc_dom_x86.c
--- a/tools/libxc/xc_dom_x86.c Mon Jun 18 18:02:30 2007 -0700
+++ b/tools/libxc/xc_dom_x86.c Tue Jun 19 02:03:13 2007 -0700
@@ -23,6 +23,7 @@
#include "xg_private.h"
#include "xc_dom.h"
#include "xenctrl.h"
+#include "bootparam.h"

/* ------------------------------------------------------------------------ */

@@ -407,6 +408,36 @@ static int alloc_magic_pages(struct xc_d

/* ------------------------------------------------------------------------ */

+static unsigned long guest_pfn_addr(struct xc_dom_image *dom, xen_pfn_t pfn,
+ size_t offset)
+{
+ return dom->parms.virt_base + pfn * PAGE_SIZE_X86 + offset;
+}
+
+static void setup_boot_params(struct xc_dom_image *dom)
+{
+ struct boot_params *params =
+ xc_dom_pfn_to_ptr(dom, dom->bootparams_pfn, 1);
+
+ params->hdr.type_of_loader = (9 << 4) | 0; /* xen v0 */
+ params->hdr.loadflags |= LOADED_HIGH | KEEP_SEGMENTS;
+
+ params->hdr.hardware_subarch = 2; /* xen */
+ params->hdr.hardware_subarch_data =
+ (uint64_t)guest_pfn_addr(dom, dom->start_info_pfn, 0);
+
+ if ( dom->ramdisk_blob )
+ {
+ params->hdr.ramdisk_image = (uint32_t)dom->ramdisk_seg.vstart;
+ params->hdr.ramdisk_size = dom->ramdisk_seg.vend - dom->ramdisk_seg.vstart;
+ }
+
+ params->hdr.cmd_line_ptr =
+ guest_pfn_addr(dom, dom->start_info_pfn,
+ offsetof(start_info_x86_32_t, cmd_line));
+ params->hdr.cmdline_size = MAX_GUEST_CMDLINE;
+}
+
static int start_info_x86_32(struct xc_dom_image *dom)
{
start_info_x86_32_t *start_info =
@@ -440,6 +471,12 @@ static int start_info_x86_32(struct xc_d
{
strncpy((char *)start_info->cmd_line, dom->cmdline, MAX_GUEST_CMDLINE);
start_info->cmd_line[MAX_GUEST_CMDLINE - 1] = '\0';
+ }
+
+ if ( dom->bootparams_pfn != 0 )
+ {
+ setup_boot_params(dom);
+ dom->start_info_pfn = dom->bootparams_pfn;
}

return 0;
@@ -528,10 +565,8 @@ static int vcpu_x86_32(struct xc_dom_ima
ctxt->user_regs.ss = FLAT_KERNEL_SS_X86_32;
ctxt->user_regs.cs = FLAT_KERNEL_CS_X86_32;
ctxt->user_regs.eip = dom->parms.virt_entry;
- ctxt->user_regs.esp =
- dom->parms.virt_base + (dom->bootstack_pfn + 1) * PAGE_SIZE_X86;
- ctxt->user_regs.esi =
- dom->parms.virt_base + (dom->start_info_pfn) * PAGE_SIZE_X86;
+ ctxt->user_regs.esp = guest_pfn_addr(dom, dom->bootstack_pfn, PAGE_SIZE_X86);
+ ctxt->user_regs.esi = guest_pfn_addr(dom, dom->start_info_pfn, 0);
ctxt->user_regs.eflags = 1 << 9; /* Interrupt Enable */

ctxt->kernel_ss = ctxt->user_regs.ss;
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