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SubjectRe: PROBLEM: zstd bzImage decompression fails for some x86_32 config on 5.9-rc1
On Mon, Sep 28, 2020 at 10:55 AM Feng Tang <feng.tang@intel.com> wrote:
>
> Hi Nick,
>
> 0day has found some kernel decomprssion failure case since 5.9-rc1 (X86_32
> build), and it could be related with ZSTD code, though initially we bisected
> to some other commits.
>
> The error messages are:
>
> early console in setup code
> Wrong EFI loader signature.
> early console in extract_kernel
> input_data: 0x046f50b4
> input_len: 0x01ebbeb6
> output: 0x01000000
> output_len: 0x04fc535c
> kernel_total_size: 0x055f5000
> needed_size: 0x055f5000
>
> Decompressing Linux...
>
> ZSTD-compressed data is corrupt
>
> This could be reproduced by compiling the kernel with attached config,
> and use QEMU to boot it.
>
> We suspect it could be related with the kernel size, as we only see
> it on big kernel, and some more info are:
>
> * If we remove a lot of kernel config to build a much smaller kernel,
> it will boot fine
>
> * If we change the zstd algorithm from zstd22 to zstd19, the kernel will
> boot fine with below patch
>

Hi,

Recently, Debian has updated initramfs-tools/initramfs-tools-core packages
with ZSTD support:

[ /usr/sbin/mkinitramfs ]

case "${compress}" in
gzip) # If we're doing a reproducible build, use gzip -n
if [ -n "${SOURCE_DATE_EPOCH}" ]; then
compress="gzip -n"
# Otherwise, substitute pigz if it's available
elif command -v pigz >/dev/null; then
compress=pigz
fi
;;
lz4) compress="lz4 -9 -l" ;;
zstd) compress="zstd -q -19 -T0" ;;
xz) compress="xz --check=crc32"
# If we're not doing a reproducible build, enable multithreading
test -z "${SOURCE_DATE_EPOCH}" && compress="$compress --threads=0"
;;
bzip2|lzma|lzop)
# no parameters needed
;;
*) echo "W: Unknown compression command ${compress}" >&2 ;;
esac

As you can see it uses compression-level 19 for ZSTD.
Maybe it is good to change from 22 to 19 in the Linux-kernel sources?

Thanks.

Regards,
- Sedat -

> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 3962f59..8fe71ba 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -147,7 +147,7 @@ $(obj)/vmlinux.bin.lzo: $(vmlinux.bin.all-y) FORCE
> $(obj)/vmlinux.bin.zst: $(vmlinux.bin.all-y) FORCE
> - $(call if_changed,zstd22)
> + $(call if_changed,zstd)
>
>
> Please let me know if you need more info, and sorry for the late report
> as we just tracked down to this point.
>
> Thanks,
> Feng
>
>
>

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