linux-kernel - perf: bench/sched-messaging.c:73:13: error: 'dummy' may be used uninitialized

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Date:   Tue, 13 Jul 2021 20:40:28 +0530
From:   Naresh Kamboju <naresh.kamboju@...aro.org>
To:     perf-users <perf-users@...aro.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-stable <stable@...r.kernel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Leo Yan <leo.yan@...aro.org>,
        Anders Roxell <anders.roxell@...aro.org>
Subject: perf: bench/sched-messaging.c:73:13: error: 'dummy' may be used uninitialized

LKFT have noticed these warnings / errors when we have updated gcc version from
gcc-9 to gcc-11 on stable-rc linux-5.4.y branch. I have provided the steps to
reproduce in this email below.

Following perf builds failed with gcc-11 with linux-5.4.y branch.
- build-arm-gcc-11-perf
- build-arm64-gcc-11-perf
- build-i386-gcc-11-perf
- build-x86-gcc-11-perf

Build error log:
--------------------
find: 'x86_64-linux-gnu-gcc/arch': No such file or directory
error: Found argument '-I' which wasn't expected, or isn't valid in this context
USAGE:
    sccache [FLAGS] [OPTIONS] [cmd]...
For more information try --help
error: Found argument '-I' which wasn't expected, or isn't valid in this context
USAGE:
    sccache [FLAGS] [OPTIONS] [cmd]...
For more information try --help

In function 'ready',
    inlined from 'sender' at bench/sched-messaging.c:87:2:
bench/sched-messaging.c:73:13: error: 'dummy' may be used
uninitialized [-Werror=maybe-uninitialized]
   73 |         if (write(ready_out, &dummy, 1) != 1)
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from bench/sched-messaging.c:22:
bench/sched-messaging.c: In function 'sender':
/usr/x86_64-linux-gnu/include/unistd.h:366:16: note: by argument 2 of
type 'const void *' to 'write' declared here
  366 | extern ssize_t write (int __fd, const void *__buf, size_t __n) __wur;
      |                ^~~~~
bench/sched-messaging.c:69:14: note: 'dummy' declared here
   69 |         char dummy;
      |              ^~~~~
cc1: all warnings being treated as errors

ref:
https://builds.tuxbuild.com/1vEIWryaujwVtL4wmodXkz1djUa/
https://builds.tuxbuild.com/1vEIX7NTo5OpaN9nrs2UvO74oxB/

Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>

Steps to reproduce:
---------------------------
tuxmake --runtime podman --target-arch x86_64 --toolchain gcc-11
--kconfig defconfig --kconfig-add
https://builds.tuxbuild.com/1vEIWryaujwVtL4wmodXkz1djUa/config headers
kernel modules perf

--
Linaro LKFT
https://lkft.linaro.org