Re: [PATCH 12/12] tests: Add a BTF reproducible generation test

[Alan Maguire <alan.maguire@oracle.com>]

On 12/04/2024 22:16, Arnaldo Carvalho de Melo wrote:
> From: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
>   $ time tests/reproducible_build.sh vmlinux
>   Parallel reproducible DWARF Loading/Serial BTF encoding: Ok
> 
>   real  1m13.844s
>   user  3m3.601s
>   sys   0m9.049s
>   $
> 
> If the number of threads started by pahole is different than what was
> requests via its -j command line option, it will fail as well as if the
> output of 'bpftool btf dump' differs from the BTF encoded totally
> serially to one of the detached BTF encoded using reproducible DWARF
> loading/BTF encoding.
> 
> Cc: Alan Maguire <alan.maguire@oracle.com>
> Cc: Kui-Feng Lee <kuifeng@fb.com>
> Cc: Thomas Weißschuh <linux@weissschuh.net>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
>  tests/reproducible_build.sh | 56 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
>  create mode 100755 tests/reproducible_build.sh
> 

great to have a test for this! a few small things below but
for the series

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>

> diff --git a/tests/reproducible_build.sh b/tests/reproducible_build.sh
> new file mode 100755
> index 0000000000000000..9c72d548c2a21136
> --- /dev/null
> +++ b/tests/reproducible_build.sh
> @@ -0,0 +1,56 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0-only
> +#
> +# Test if BTF generated serially matches reproducible parallel DWARF loading + serial BTF encoding
> +# Arnaldo Carvalho de Melo <acme@redhat.com> (C) 2024-
> +
> +vmlinux=$1

nit: might be worth having a usage check/error for the vmlinux binary here.

> +outdir=$(mktemp -d /tmp/reproducible_build.sh.XXXXXX)
> +
> +echo -n "Parallel reproducible DWARF Loading/Serial BTF encoding: "
> +
> +test -n "$VERBOSE" && printf "\nserial encoding...\n"
> +
> +pahole --btf_encode_detached=$outdir/vmlinux.btf.serial $vmlinux

suggestion here; what about adding --btf_features=all as this would mean
we'd be encoding all the standard kernel features? we'd need to do the
same below in the thread loop. without that we're missing out on a few
features that the kernel builds use in BTF encoding, and we probably
want to ensure that we're testing as close to a real kernel BTF encoding
scenario as possible.

> +bpftool btf dump file $outdir/vmlinux.btf.serial > $outdir/bpftool.output.vmlinux.btf.serial
> +
> +nr_proc=$(getconf _NPROCESSORS_ONLN)
> +
> +for threads in $(seq $nr_proc) ; do
> +	test -n "$VERBOSE" && echo $threads threads encoding
> +	pahole -j$threads --reproducible_build --btf_encode_detached=$outdir/vmlinux.btf.parallel.reproducible $vmlinux &
> +	pahole=$!
> +	# HACK: Wait a bit for pahole to start its threads
> +	sleep 0.3s
> +	# PID part to remove ps output headers
> +	nr_threads_started=$(ps -L -C pahole | grep -v PID | wc -l)
> +
> +	if [ $threads -gt 1 ] ; then
> +		((nr_threads_started -= 1))
> +	fi
> +
> +	if [ $threads != $nr_threads_started ] ; then
> +		echo "ERROR: pahole asked to start $threads encoding threads, started $nr_threads_started"
> +		exit 1;
> +	fi
> +
> +	# ps -L -C pahole | grep -v PID | nl
> +	test -n "$VERBOSE" && echo $nr_threads_started threads started
> +	wait $pahole
> +	rm -f $outdir/bpftool.output.vmlinux.btf.parallel.reproducible
> +	bpftool btf dump file $outdir/vmlinux.btf.parallel.reproducible > $outdir/bpftool.output.vmlinux.btf.parallel.reproducible
> +	test -n "$VERBOSE" && echo "diff from serial encoding:"
> +	diff -u $outdir/bpftool.output.vmlinux.btf.serial $outdir/bpftool.output.vmlinux.btf.parallel.reproducible > $outdir/diff
> +	if [ -s $outdir/diff ] ; then
> +		echo "ERROR: BTF generated from DWARF in parallel is different from the one generated in serial!"
> +		exit 1
> +	fi
> +	test -n "$VERBOSE" && echo -----------------------------
> +done
> +
> +rm $outdir/*
> +rmdir $outdir
> +
> +echo "Ok"
> +
> +exit 0