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From:   Lorenz Bauer <lmb@cloudflare.com>
Date:   Fri, 2 Oct 2020 11:08:04 +0100
Message-ID: <CACAyw99ji02q3XngQS=KbRtebRipNU4P3kUbV1ULeVy64MA3mg@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2 2/4] selftests: bpf: Add helper to compare
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To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        Martin KaFai Lau <kafai@fb.com>,
        Shuah Khan <shuah@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        kernel-team <kernel-team@cloudflare.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
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On Thu, 1 Oct 2020 at 18:11, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> >
> > I think this might be the same problem I fixed for libbpf with [0].
> > Turns out, GCC explicitly calls out (somewhere in their docs) that
> > uninitialized variable warnings work only when compiled in optimized
> > mode, because some internal data structures used to detect this are
> > only maintained in optimized mode build.
> >
> > Laurenz, can you try compiling your example with -O2?
>
> All of my experiments I did with -O2.

If anybody wants to play with this more: https://godbolt.org/z/77P6P9

Seems like red hat GCC has some special sauce that fixes this behaviour?

-- 
Lorenz Bauer  |  Systems Engineer
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