Re: test_vsyscall.c:500:22: warning: '__builtin_memcmp_eq' specified bound 4096 exceeds source size 0

From: Naresh Kamboju <naresh.kamboju@linaro.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	skhan@linuxfoundation.org
Cc: linux-stable <stable@vger.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	lkft-triage@lists.linaro.org, X86 ML <x86@kernel.org>,
	Shuah Khan <shuah@kernel.org>, Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jann Horn <jannh@google.com>, John Hubbard <jhubbard@nvidia.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Anders Roxell <anders.roxell@linaro.org>
Subject: Re: test_vsyscall.c:500:22: warning: '__builtin_memcmp_eq' specified bound 4096 exceeds source size 0
Date: Thu, 6 Jan 2022 15:19:59 +0530	[thread overview]
Message-ID: <CA+G9fYuRUsmsj+f3RXAKpvX2k=YJwxj4-_MqWzi1L-D9YdE5Cg@mail.gmail.com> (raw)
In-Reply-To: <Yda3L0givFBDZtXs@kroah.com>

On Thu, 6 Jan 2022 at 15:02, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Thu, Jan 06, 2022 at 02:55:53PM +0530, Naresh Kamboju wrote:
> > While building selftests the following warnings were noticed for x86_64
> > architecture on Linux stable v5.15.13 kernel.
> >
> > metadata:
> >   git repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
> >   git commit: 734eb1fd2073f503f5c6b44f1c0d453ca6986b84
> >   git describe: v5.15.13
> >   toolchain":  gcc-11
> >   kernel-config: https://builds.tuxbuild.com/23HFo8abXIL6i4FFfSYiJlqAYMW/config
> >
> > x86_64-linux-gnu-gcc -m64 -o \
> > /home/tuxbuild/.cache/tuxmake/builds/current/kselftest/x86/test_vsyscall_64 \
> >  -O2 -g -std=gnu99 -pthread -Wall -no-pie \
> >  -DCAN_BUILD_64 test_vsyscall.c helpers.h -lrt -ldl
> >
> > test_vsyscall.c: In function 'test_process_vm_readv':
> > test_vsyscall.c:500:22: warning: '__builtin_memcmp_eq' specified bound
> > 4096 exceeds source size 0 [-Wstringop-overread]
> >   500 |                 if (!memcmp(buf, (const void
> > *)0xffffffffff600000, 4096)) {
> >       |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> >
> > Build link:
> > https://builds.tuxbuild.com/23HFo8abXIL6i4FFfSYiJlqAYMW/
> >
> > # To install tuxmake on your system globally:
> > # sudo pip3 install -U tuxmake
> >
> > tuxmake --runtime podman --target-arch x86_64 --toolchain gcc-11 \
> >  --kconfig https://builds.tuxbuild.com/23HFo8abXIL6i4FFfSYiJlqAYMW/config \
> >  cpupower headers kernel kselftest kselftest-merge modules
>
> Is this a new regression from 5.15.0?  Is it also present on Linus's tree?

This build warning is not present in Linus's tree.
Following patch to be backported to 5.15.x

---
From dd40f44eabe1e122c6852fabb298aac05b083fce Mon Sep 17 00:00:00 2001
From: Shuah Khan <skhan@linuxfoundation.org>
Date: Thu, 21 Oct 2021 15:33:33 -0600
Subject: selftests: x86: fix [-Wstringop-overread] warn in
 test_process_vm_readv()

Fix the following [-Wstringop-overread] by passing in the variable
instead of the value.

test_vsyscall.c: In function ‘test_process_vm_readv’:
test_vsyscall.c:500:22: warning: ‘__builtin_memcmp_eq’ specified bound
4096 exceeds source size 0 [-Wstringop-overread]
  500 |                 if (!memcmp(buf, (const void
*)0xffffffffff600000, 4096)) {
      |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

- Naresh