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Subject: Re: [PATCH v2] checkpatch: do not apply "initialise globals to 0"
 check to BPF progs
From:   Joe Perches <joe@perches.com>
To:     Song Liu <songliubraving@fb.com>, linux-kernel@vger.kernel.org
Cc:     bpf@vger.kernel.org, Andy Whitcroft <apw@canonical.com>
Date:   Tue, 09 Feb 2021 09:24:15 -0800
In-Reply-To: <20210209170013.3475063-1-songliubraving@fb.com>
References: <20210209170013.3475063-1-songliubraving@fb.com>
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On Tue, 2021-02-09 at 09:00 -0800, Song Liu wrote:
> BPF programs explicitly initialise global variables to 0 to make sure
> clang (v10 or older) do not put the variables in the common section.
> Skip "initialise globals to 0" check for BPF programs to elimiate error
> messages like:
> 
> ????ERROR: do not initialise globals to 0
> ????#19: FILE: samples/bpf/tracex1_kern.c:21:
> 
> Cc: Andy Whitcroft <apw@canonical.com>
> Cc: Joe Perches <joe@perches.com>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> 
> ---
> Changes v1 => v2:
> ??1. Add function exclude_global_initialisers() to keep the code clean.

thanks.  trivia and a question:

> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -2428,6 +2428,15 @@ sub get_raw_comment {
> ?	return $comment;
> ?}
> 
> +sub exclude_global_initialisers {
> +	my ($realfile) = @_;
> +
> +	# Do not check for BPF programs (tools/testing/selftests/bpf/progs/*.c, samples/bpf/*_kern.c, *.bpf.c).
> +	return $realfile =~ /^tools\/testing\/selftests\/bpf\/progs\/.*\.c/ ||
> +		$realfile =~ /^samples\/bpf\/.*_kern.c/ ||

The checkpatch convention commonly used for $realfile comparisons
to file patterns with directory paths is m@...@

	return $realfile =~ m@^tools/testing/selftests/bpf/progs/.*\.c@ ||
		$realfile =~ m@^samples/bpf/.*_kern\.c@ ||

> +		$realfile =~ /.bpf.c$/;

And lastly, is this pattern meant to escape the periods?
I presume so, but if not, the leading period isn't useful.

Maybe:
		$realfile =~ m@/bpf/.*\.bpf\.c$@;

$ git ls-files | grep "\.bpf\.c$"
kernel/bpf/preload/iterators/iterators.bpf.c
tools/bpf/bpftool/skeleton/pid_iter.bpf.c
tools/bpf/bpftool/skeleton/profiler.bpf.c
tools/bpf/runqslower/runqslower.bpf.c

vs

$ git ls-files | grep ".bpf.c$"
drivers/net/hyperv/netvsc_bpf.c
drivers/net/netdevsim/bpf.c
kernel/bpf/preload/iterators/iterators.bpf.c
lib/test_bpf.c
net/core/lwt_bpf.c
net/ipv4/tcp_bpf.c
net/ipv4/udp_bpf.c
net/netfilter/xt_bpf.c
net/sched/act_bpf.c
net/sched/cls_bpf.c
samples/bpf/test_lwt_bpf.c
tools/bpf/bpftool/skeleton/pid_iter.bpf.c
tools/bpf/bpftool/skeleton/profiler.bpf.c
tools/bpf/runqslower/runqslower.bpf.c
tools/build/feature/test-bpf.c
tools/build/feature/test-libbpf.c
tools/lib/bpf/bpf.c
tools/lib/bpf/libbpf.c
tools/perf/tests/bpf.c
tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
tools/testing/selftests/bpf/prog_tests/xdp_bpf2bpf.c
tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c
tools/testing/selftests/bpf/progs/test_xdp_bpf2bpf.c
tools/testing/selftests/net/reuseport_bpf.c
tools/testing/selftests/seccomp/seccomp_bpf.c