Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230724131741.954624-1-james.clark@arm.com> <CANiq72nJP+i10CZysua0QU=V=Cn=jdnLuV8KOqm6_NNFdg9S3w@mail.gmail.com>
 <6c99392f-6189-1835-3090-d5c7f95edaf9@arm.com>
In-Reply-To: <6c99392f-6189-1835-3090-d5c7f95edaf9@arm.com>
From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Tue, 25 Jul 2023 12:33:41 +0200
Message-ID: <CANiq72nPxb8p5YCTohGg5e3c4gPTYsfh8fB182D_SwO-rQm9pg@mail.gmail.com>
Subject: Re: [PATCH] scripts/kallsyms: Fix build failure by setting errno
 before calling getline()
To:     James Clark <james.clark@arm.com>
Cc:     linux-kbuild@vger.kernel.org, masahiroy@kernel.org,
        linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Zhen Lei <thunder.leizhen@huawei.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>, Nicolas Schier <n.schier@avm.de>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, Jul 25, 2023 at 10:55=E2=80=AFAM James Clark <james.clark@arm.com> =
wrote:
>
> But I just checked now and it's just bear [1] that causes the issue.
> Maybe it sets errno before forking and that persists in the child
> processes? Not 100% sure how it works. I did debug scripts/kallsyms and
> errno was already set on the first line of main(), so it's not some
> other library call in kallsyms that is setting it but not being checked.

I think this is https://github.com/rizsotto/Bear/issues/469: bear
preloads a library which was setting it to non-zero.

Now, even if bear was breaking a guarantee C programs have (`errno`
for the initial thread at program startup is meant to be 0 according
to the C standard), it is still a good idea to set `errno` to zero
here in case something else happens to change `errno` within
`kallsyms` in the future.

With the repro and the `bear` link issue added:

    Reviewed-by: Miguel Ojeda <ojeda@kernel.org>

Cheers,
Miguel