On 15.07.2022 15:26, Andrew Cooper wrote:
> While Xen's current VMA means it works, the mawk fix (i.e. using $((0xN)) in
> the shell) isn't portable in 32bit shells. See the code comment for the fix.
>
> The fix found a second latent bug. Recombining $vma_hi/lo should have used
> printf "%s%08x" and only worked previously because $vma_lo had bits set in
> it's top nibble. Combining with the main fix, %08x becomes %07x.
>
> Fixes: $XXX patch 1
> Reported-by: Jan Beulich <jbeul...@suse.com>
> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
Reviewed-by: Jan Beulich <jbeul...@suse.com>
with, I guess, ...
> --- a/xen/tools/check-endbr.sh
> +++ b/xen/tools/check-endbr.sh
> @@ -61,19 +61,36 @@ ${OBJDUMP} -j .text $1 -d -w | grep ' endbr64 *$' |
> cut -f 1 -d ':' > $VALID &
> # the lower bits, rounding integers to the nearest 4k.
> #
> # Instead, use the fact that Xen's .text is within a 1G aligned region,
> and
> -# split the VMA in half so AWK's numeric addition is only working on 32
> bit
> -# numbers, which don't lose precision.
> +# split the VMA so AWK's numeric addition is only working on <32 bit
> +# numbers, which don't lose precision. (See point 5)
> #
> # 4) MAWK doesn't support plain hex constants (an optional part of the POSIX
> # spec), and GAWK and MAWK can't agree on how to work with hex constants
> in
> # a string. Use the shell to convert $vma_lo to decimal before passing to
> # AWK.
> #
> +# 5) Point 4 isn't fully portable. POSIX only requires that $((0xN)) be
> +# evaluated as long, which in 32bit shells turns negative if bit 31 of the
> +# VMA is set. AWK then interprets this negative number as a double before
> +# adding the offsets from the binary grep.
> +#
> +# Instead of doing an 8/8 split with vma_hi/lo, do a 9/7 split.
> +#
> +# The consequence of this is that for all offsets, $vma_lo + offset needs
> +# to be less that 256M (i.e. 7 nibbles) so as to be successfully
> recombined
> +# with the 9 nibbles of $vma_hi. This is fine; .text is at the start of a
> +# 1G aligned region, and Xen is far far smaller than 256M, but leave
> safety
> +# check nevertheless.
> +#
> eval $(${OBJDUMP} -j .text $1 -h |
> - $AWK '$2 == ".text" {printf "vma_hi=%s\nvma_lo=%s\n", substr($4, 1, 8),
> substr($4, 9, 16)}')
> + $AWK '$2 == ".text" {printf "vma_hi=%s\nvma_lo=%s\n", substr($4, 1, 9),
> substr($4, 10, 16)}')
>
> ${OBJCOPY} -j .text $1 -O binary $TEXT_BIN
>
> +bin_sz=$(stat -c '%s' $TEXT_BIN)
> +[ "$bin_sz" -ge $(((1 << 28) - $vma_lo)) ] &&
> + { echo "$MSG_PFX Error: .text offsets can exceed 256M" >&2; exit 1; }
... s/can/cannot/ ?
Jan
