Header checksum error when extracting vmlinux from kernel

HotDogEnemy · 2021-08-08 20:09:40

So I'm trying to obtain a vmlinux image of the vanilla kernel for debugging a crash dump, but I keep getting errors.

I used "dd if=/boot/vmlinuz-linux bs=1 skip=5337607 | zcat > vmlinux " to try and extract the vmlinux file, but it fails with the following error code:

~ > dd if=/boot/vmlinuz-linux bs=1 skip=5337607 | zcat > vmlinux
gzip: stdin: header checksum 0xb238 != computed checksum 0xba3e

I've tried with the -f and -n flag for zcat, but it still didn't work even then. Trying this with linux-zen with the proper values also gives the same error.

Help would be appreciated.

Last edited by HotDogEnemy (2021-08-08 20:11:49)

seth · 2021-08-08 21:00:05

Where does the offset come from?
Try https://github.com/torvalds/linux/blob/ … ct-vmlinux

nb. that the uncompressed image will probably not contain the debug symbols and you'll not be able to create the System.map w/ https://github.com/torvalds/linux/blob/ … s/mksysmap

HotDogEnemy · 2021-08-08 21:23:05

~ > od -t x1 -A d /boot/vmlinuz-linux | grep "1f 8b 08"
5337600 4b 43 46 47 5f 53 54 1f 8b 08 02 03 94 3c c9 72

5337600 + 7 gives the offset, since the 1f 8b 08 string starts after 8 positions from the 5337600.

If the uncompressed image does not contain the debug symbols, how should I go about creating the system.map? It's my first time diving into this topic so I'm lost.

seth · 2021-08-08 21:34:46

The kernel is rather not gzip compressed… I guess you googled hat command and found an entry from errr… 2007?

If the uncompressed image does not contain the debug symbols

You need a kernel image that still has them.
If you built the kernel yourself it's in the source directory, https://wiki.archlinux.org/title/Kdump

HotDogEnemy · 2021-08-08 22:00:31

So I'm following this archwiki page ( https://wiki.archlinux.org/title/Kernel … ild_System ) to compile the default kernel to have vmlinux in it, is commenting the following lines in the PKGBUILD all I have to do?:

echo "Stripping vmlinux..."
  strip -v $STRIP_STATIC "$builddir/vmlinux"

Last edited by HotDogEnemy (2021-08-08 22:07:05)

loqs · 2021-08-08 23:04:41

Is there anything recorded in the journal for the issue?

HotDogEnemy · 2021-08-08 23:05:56

Nope, the symptoms resemble a kernel panic, keyboard and mouse unresponsive, black screen with faint vertical grey bars and any audio that was playing keeps looping. System LEDs stay on.

seth · 2021-08-09 06:54:05

Not stripping will preserve the symbol names.

Have you btw. tried just the regular compressed vmlinuz on a present dump?
(crash is supposd to be able to handle that and I assume we end in some kerne module anyway - which would already narrow the culprit)

HotDogEnemy · 2021-08-09 10:55:23

I haven't yet gotten kexec to run on my computer, so I tested it on a vm and generated a crash report on it. Trying to use crash with the vmlinuz-linux file and crash dump results in it giving an error saying "vmlinuz : unsupported file format".

seth · 2021-08-09 11:39:22

Then use the previously linked script to extract the uncompressed kernel.

HotDogEnemy · 2021-08-10 18:30:10

I checked out the script, but it didn't work- the vmlinux file generated isn't usable by crash, it gives an "unsupported file format error". I tried using the vmlinux at /usr/src/linux, but crash says "crash: vmlinux: no debugging data available". I'm not sure why, the linux-headers and the kernel package are both the same version.

seth · 2021-08-10 21:01:34

crash: vmlinux: no debugging data available

The kernel was built either w/o "-g" or it was stripped… try

- options=('!strip')
+ options=('debug' '!strip')

HotDogEnemy · 2021-08-14 22:25:27

So, I tried compiling the kernel with the 'debug' option just like you said. The vmlinux that gets installed at /usr/src/linux/vmlinux still gives this error when used with crash:

[root@archlinux ~]# crash /Usr/src/linux/vmlinux  /root/crashdump-2021-08-15-02\:54\:01.dump

This is even with the 'debug' line added to the options in the PKGBUILD. The file stats also show that it is not stripped and was created when I compiled and installed the kernel and kernel headers:

~ > file /usr/src/linux/vmlinux
/usr/src/linux/vmlinux: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, BuildID[sha1]=e0db7571278672e079794156fc263292cb2a6e3c, not stripped
~ > stat /usr/src/linux/vmlinux
  File: /usr/src/linux/vmlinux
    Size: 81185808        Blocks: 144008     IO Block: 4096   regular file
    Device: 811h/2065d      Inode: 6307586     Links: 1
    Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
    Access: 2021-08-15 02:57:04.383830237 +0530
    Modify: 2021-08-14 00:56:20.000000000 +0530
    Change: 2021-08-15 02:37:06.825589822 +0530
     Birth: 2021-08-15 02:37:06.701587134 +0530

Using the vmlinux generated by using the extract-vmlinux script above also fails with the following output:

[root@archlinux ~]# crash /home/shivodit/vmlinux /root/crashdump-2021-08-15-02\:54\:01.dump

crash 7.3.0
Copyright (C) 2002-2021  Red Hat, Inc.
Copyright (C) 2004, 2005, 2006, 2010  IBM Corporation
Copyright (C) 1999-2006  Hewlett-Packard Co
Copyright (C) 2005, 2006, 2011, 2012  Fujitsu Limited
Copyright (C) 2006, 2007  VA Linux Systems Japan K.K.
Copyright (C) 2005, 2011, 2020-2021  NEC Corporation
Copyright (C) 1999, 2002, 2007  Silicon Graphics, Inc.
Copyright (C) 1999, 2000, 2001, 2002  Mission Critical Linux, Inc.
This program is free software, covered by the GNU General Public License,
an you are welcome to change it and/or distribute copies of it under
certain conditions.  Enter "help copying" to see the conditions.
This program has absolutely no warranty.  Enter "help warranty" for details.

crash: /home/shivodit/vmlinux: no .gnu_debuglink section

crash: /home/shivodit/vmlinux: no debugging data available

However, the vmlinux file in the build directory (~/build/linux/src/archlinux-linux/vmlinux in my case) works flawlessly with crash.

In case you want to see what PKGBUILD I'm using, here it is:

# Maintainer: Jan Alexander Steffens (heftig) <heftig@archlinux.org>

pkgbase=linux
pkgver=5.13.9.arch1
pkgrel=1
pkgdesc='Linux'
_srctag=v${pkgver%.*}-${pkgver##*.}
url="https://github.com/archlinux/linux/commits/$_srctag"
arch=(x86_64)
license=(GPL2)
makedepends=(
  bc kmod libelf pahole cpio perl tar xz
  xmlto python-sphinx python-sphinx_rtd_theme graphviz imagemagick
  git
)
options=('debug' '!strip')
_srcname=archlinux-linux
source=(
  "$_srcname::git+https://github.com/archlinux/linux?signed#tag=$_srctag"
  config         # the main kernel config file
)
validpgpkeys=(
  'ABAF11C65A2970B130ABE3C479BE3E4300411886'  # Linus Torvalds
  '647F28654894E3BD457199BE38DBBDC86092693E'  # Greg Kroah-Hartman
  'A2FF3A36AAA56654109064AB19802F8B0D70FC30'  # Jan Alexander Steffens (heftig)
  'C7E7849466FE2358343588377258734B41C31549'  # David Runge <dvzrv@archlinux.org>
)
sha256sums=('SKIP'
            '6b3672ffafb1b29bde3eb76dc27d1a41cc2f8349068a6532717c3d4764a2d238')

export KBUILD_BUILD_HOST=archlinux
export KBUILD_BUILD_USER=$pkgbase
export KBUILD_BUILD_TIMESTAMP="$(date -Ru${SOURCE_DATE_EPOCH:+d @$SOURCE_DATE_EPOCH})"

prepare() {
  cd $_srcname

  echo "Setting version..."
  scripts/setlocalversion --save-scmversion
  echo "-$pkgrel" > localversion.10-pkgrel
  echo "${pkgbase#linux}" > localversion.20-pkgname

  local src
  for src in "${source[@]}"; do
    src="${src%%::*}"
    src="${src##*/}"
    [[ $src = *.patch ]] || continue
    echo "Applying patch $src..."
    patch -Np1 < "../$src"
  done

  echo "Setting config..."
  cp ../config .config
  make olddefconfig

  make -s kernelrelease > version
  echo "Prepared $pkgbase version $(<version)"
}

build() {
  cd $_srcname
  make all
  
}

_package() {
  pkgdesc="The $pkgdesc kernel and modules"
  depends=(coreutils kmod initramfs)
  optdepends=('crda: to set the correct wireless channels of your country'
              'linux-firmware: firmware images needed for some devices')
  provides=(VIRTUALBOX-GUEST-MODULES WIREGUARD-MODULE)
  replaces=(virtualbox-guest-modules-arch wireguard-arch)

  cd $_srcname
  local kernver="$(<version)"
  local modulesdir="$pkgdir/usr/lib/modules/$kernver"

  echo "Installing boot image..."
  # systemd expects to find the kernel here to allow hibernation
  # https://github.com/systemd/systemd/commit/edda44605f06a41fb86b7ab8128dcf99161d2344
  install -Dm644 "$(make -s image_name)" "$modulesdir/vmlinuz"

  # Used by mkinitcpio to name the kernel
  echo "$pkgbase" | install -Dm644 /dev/stdin "$modulesdir/pkgbase"

  echo "Installing modules..."
  make INSTALL_MOD_PATH="$pkgdir/usr" INSTALL_MOD_STRIP=1 modules_install

  # remove build and source links
  rm "$modulesdir"/{source,build}
}

_package-headers() {
  pkgdesc="Headers and scripts for building modules for the $pkgdesc kernel"
  depends=(pahole)

  cd $_srcname
  local builddir="$pkgdir/usr/lib/modules/$(<version)/build"

  echo "Installing build files..."
  install -Dt "$builddir" -m644 .config Makefile Module.symvers System.map \
    localversion.* version vmlinux
  install -Dt "$builddir/kernel" -m644 kernel/Makefile
  install -Dt "$builddir/arch/x86" -m644 arch/x86/Makefile
  cp -t "$builddir" -a scripts

  # add objtool for external module building and enabled VALIDATION_STACK option
  install -Dt "$builddir/tools/objtool" tools/objtool/objtool

  # add xfs and shmem for aufs building
  mkdir -p "$builddir"/{fs/xfs,mm}

  echo "Installing headers..."
  cp -t "$builddir" -a include
  cp -t "$builddir/arch/x86" -a arch/x86/include
  install -Dt "$builddir/arch/x86/kernel" -m644 arch/x86/kernel/asm-offsets.s

  install -Dt "$builddir/drivers/md" -m644 drivers/md/*.h
  install -Dt "$builddir/net/mac80211" -m644 net/mac80211/*.h

  # https://bugs.archlinux.org/task/13146
  install -Dt "$builddir/drivers/media/i2c" -m644 drivers/media/i2c/msp3400-driver.h

  # https://bugs.archlinux.org/task/20402
  install -Dt "$builddir/drivers/media/usb/dvb-usb" -m644 drivers/media/usb/dvb-usb/*.h
  install -Dt "$builddir/drivers/media/dvb-frontends" -m644 drivers/media/dvb-frontends/*.h
  install -Dt "$builddir/drivers/media/tuners" -m644 drivers/media/tuners/*.h

  # https://bugs.archlinux.org/task/71392
  install -Dt "$builddir/drivers/iio/common/hid-sensors" -m644 drivers/iio/common/hid-sensors/*.h

  echo "Installing KConfig files..."
  find . -name 'Kconfig*' -exec install -Dm644 {} "$builddir/{}" \;

  echo "Removing unneeded architectures..."
  local arch
  for arch in "$builddir"/arch/*/; do
    [[ $arch = */x86/ ]] && continue
    echo "Removing $(basename "$arch")"
    rm -r "$arch"
  done

  echo "Removing documentation..."
  rm -r "$builddir/Documentation"

  echo "Removing broken symlinks..."
  find -L "$builddir" -type l -printf 'Removing %P\n' -delete

  echo "Removing loose objects..."
  find "$builddir" -type f -name '*.o' -printf 'Removing %P\n' -delete

  echo "Stripping build tools..."
  local file
  while read -rd '' file; do
    case "$(file -bi "$file")" in
      application/x-sharedlib\;*)      # Libraries (.so)
        strip -v $STRIP_SHARED "$file" ;;
      application/x-archive\;*)        # Libraries (.a)
        strip -v $STRIP_STATIC "$file" ;;
      application/x-executable\;*)     # Binaries
        strip -v $STRIP_BINARIES "$file" ;;
      application/x-pie-executable\;*) # Relocatable binaries
        strip -v $STRIP_SHARED "$file" ;;
    esac
  done < <(find "$builddir" -type f -perm -u+x ! -name vmlinux -print0)

  echo "Stripping vmlinux..."
  strip -v $STRIP_STATIC "$builddir/vmlinux"

  echo "Adding symlink..."
  mkdir -p "$pkgdir/usr/src"
  ln -sr "$builddir" "$pkgdir/usr/src/$pkgbase"
}

_package-docs() {
  pkgdesc="Documentation for the $pkgdesc kernel"

  cd $_srcname
  local builddir="$pkgdir/usr/lib/modules/$(<version)/build"

  echo "Installing documentation..."
  local src dst
  while read -rd '' src; do
    dst="${src#Documentation/}"
    dst="$builddir/Documentation/${dst#output/}"
    install -Dm644 "$src" "$dst"
  done < <(find Documentation -name '.*' -prune -o ! -type d -print0)

  echo "Adding symlink..."
  mkdir -p "$pkgdir/usr/share/doc"
  ln -sr "$builddir/Documentation" "$pkgdir/usr/share/doc/$pkgbase"
}

pkgname=("$pkgbase" "$pkgbase-headers")
for _p in "${pkgname[@]}"; do
  eval "package_$_p() {
    $(declare -f "_package${_p#$pkgbase}")
    _package${_p#$pkgbase}
  }"
done

# vim:set ts=8 sts=2 sw=2 et:

Arch Linux

#1 2021-08-08 20:09:40

Header checksum error when extracting vmlinux from kernel

#2 2021-08-08 21:00:05

Re: Header checksum error when extracting vmlinux from kernel

#3 2021-08-08 21:23:05

Re: Header checksum error when extracting vmlinux from kernel

#4 2021-08-08 21:34:46

Re: Header checksum error when extracting vmlinux from kernel

#5 2021-08-08 22:00:31

Re: Header checksum error when extracting vmlinux from kernel

#6 2021-08-08 23:04:41

Re: Header checksum error when extracting vmlinux from kernel

#7 2021-08-08 23:05:56

Re: Header checksum error when extracting vmlinux from kernel

#8 2021-08-09 06:54:05

Re: Header checksum error when extracting vmlinux from kernel

#9 2021-08-09 10:55:23

Re: Header checksum error when extracting vmlinux from kernel

#10 2021-08-09 11:39:22

Re: Header checksum error when extracting vmlinux from kernel

#11 2021-08-10 18:30:10

Re: Header checksum error when extracting vmlinux from kernel

#12 2021-08-10 21:01:34

Re: Header checksum error when extracting vmlinux from kernel

#13 2021-08-14 22:25:27

Re: Header checksum error when extracting vmlinux from kernel

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