Re: [PATCH bpf-next] selftests/bpf: add bpf-gcc support

From: jose.marchesi@oracle.com (Jose E. Marchesi)
To: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
	Alexei Starovoitov <ast@kernel.org>,
	bpf@vger.kernel.org, Heiko Carstens <heiko.carstens@de.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>
Subject: Re: [PATCH bpf-next] selftests/bpf: add bpf-gcc support
Date: Wed, 11 Sep 2019 12:30:44 +0200	[thread overview]
Message-ID: <8736h3nn6g.fsf@oracle.com> (raw)
In-Reply-To: <20190910234140.53363-1-iii@linux.ibm.com> (Ilya Leoshkevich's message of "Wed, 11 Sep 2019 00:41:40 +0100")

Hi Ilya.

    Now that binutils and gcc support for BPF is upstream, make use of it in
    BPF selftests using alu32-like approach. Share as much as possible of
    CFLAGS calculation with clang.

    In order to activate the new bpf-gcc support, one needs to configure
    binutils and gcc with --target=bpf and make them available in $PATH. In
    particular, gcc must be installed as `bpf-gcc`, which is the default.

    Right now with binutils 25a2915e8dba and gcc r275589 only a handful of
    tests work:

    	# ./test_progs_bpf_gcc
    	Summary: 5/39 PASSED, 1 SKIPPED, 100 FAILED

    The reason is that a lot of progs fail to build with the following
    errors:

    	error: indirect call in function, which are not supported by eBPF
    	error: too many function arguments for eBPF

    The next step is to understand those issues and fix them.

Will install your patch and take a look.

Maybe GCC is not inlining something it should be inlining, or clang may
be silently generating callx %reg instructions, or maybe there are bugs
in my diagnostics... in any case this is useful feedback :)

Thanks!