linux-kernel - Re: gcov: NULL pointer dereference with gcc 9.3.1

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Date:   Wed, 2 Jun 2021 15:22:42 +0100
From:   Luis Henriques <lhenriques@...e.de>
To:     Peter Oberparleiter <oberpar@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: gcov: NULL pointer dereference with gcc 9.3.1

On Wed, Jun 02, 2021 at 02:35:31PM +0200, Peter Oberparleiter wrote:
> On 01.06.2021 17:56, Luis Henriques wrote:
> > Hi!
> > 
> > Maybe this is a known (gcc?) issue, but I'm seeing a NULL pointer splat if
> > I instrument my kernel (or a module, more specifically) using gcc 9.3.1.
> > 
> > It looks like, during initialization in __gcov_init(), gcov_info struct is
> > invalid: the filename seems to be correct but ->function is NULL and
> > ->n_functions contains garbage.
> 
> Thanks for reporting this issue. The symptoms you're seeing look similar
> to those that occur when the struct gcov_info layout emitted by GCC does
> not match the one used by the kernel. In particular a change in the
> GCOV_COUNTER value can cause this behavior.
> 
> I've checked upstream GCC 9.3.1 and it seems to match what is used by
> the kernel for that GCC version. Could you provide the exact version of
> the compiler you are using? Both 'gcc --version' output and the GCC
> package version should help. Also what architecture are you seeing this on?

Here's the output of 'gcc --version':

gcc (SUSE Linux) 9.3.1 20200903 [revision 9790fa53b48f3a48e0f7a7ad65e2bbf3b206a7b0]
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

This is the version shipped with openSUSE Tumbleweed, and I'm using it to
compile an x86_64 kernel.  Regarding the 'package version', I'm assuming
the packages as per the distro package version, right?  Here's the data
from 'zypper info':

Information for package gcc9:
-----------------------------
Repository     : Main Repository (OSS)
Name           : gcc9
Version        : 9.3.1+git1684-3.5
Arch           : x86_64
Vendor         : openSUSE
Installed Size : 94.6 MiB
Installed      : Yes (automatically)
Status         : up-to-date
Source package : gcc9-9.3.1+git1684-3.5.src

Do you have a link with binaries I could test for upstream 9.3.1?  I
checked [1] but there's only 9.3.0.

[1] https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/

Cheers,
--
Luís