Re: [dpdk-dev] [PATCH v2] build: check functionality rather than binutils version

[Thomas Monjalon <thomas@monjalon.net>]

18/06/2020 13:56, Bruce Richardson:
> Rather than checking the binutils version number, which can lead to
> unnecessary disabling of AVX512 if fixes have been backported to distro
> versions, we can instead check the output of "as" from binutils to see if
> it is correct.
> 
> The check in the script uses the minimal assembly reproduction code posted
> to the public bug tracker for gcc/binutils for those issues [1]. If the
> binutils bug is present, the instruction parameters - specifically the
> displacement parameter - will be different in the disassembled output
> compared to the input. Therefore the check involves assembling a single
> instruction and disassembling it again, checking that the two match.
[...]
> --- /dev/null
> +++ b/buildtools/binutils-avx512-check.sh
> +MESON_BUILD_ROOT=${MESON_BUILD_ROOT:-/tmp}
> +OBJFILE=$MESON_BUILD_ROOT/binutils-avx512-check.o
> +# from https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90028
> +GATHER_PARAMS='0x8(,%ymm1,1),%ymm0{%k2}'
> +
> +# assemble vpgather to file and similarly check
> +echo "vpgatherqq $GATHER_PARAMS" | $AS --64 -o $OBJFILE -
> +objdump -d  --no-show-raw-insn $OBJFILE | grep -q $GATHER_PARAMS || {
> +	echo "vpgatherqq displacement error with as"
> +	exit 1
> +}

For the temporary OBJFILE, please use mktemp and trap for cleanup.
If you grep "mktemp" in DPDK, you will see the filename is pretty well
standardized with "dpdk." as prefix.
Thanks