new warning with GCC 13: ‘Tix_GrAddChangedRect’ accessing 16 bytes in a region of size 8 [-Wstringop-overflow]

[Quipyowert2]

GCC 13 gives a false positive on tixGrSel.c in Perl/Tk 804.036:

cc -c -I/usr/include/freetype2  -I..  -I/usr/include/freetype2 -I. -Ibitmaps  -I/usr/include/freetype2 -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2 -O2   -DVERSION=\"804.036\" -DXS_VERSION=\"804.036\" -fPIC "-I/home/nathan/perl5/perlbrew/perls/perl-5.41.2/lib/5.41.2/x86_64-linux/CORE"    tixGrSel.c
In function ‘Tix_GrMergeSelection’,
    inlined from ‘Tix_GrSelModify’ at tixGrSel.c:377:2:
tixGrSel.c:233:5: warning: ‘Tix_GrAddChangedRect’ accessing 16 bytes in a region of size 8 [-Wstringop-overflow=]
  233 |     Tix_GrAddChangedRect(wPtr, sbPtr->range, 0);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tixGrSel.c:233:5: note: referencing argument 2 of type ‘int[2][2]’
In file included from tixGrSel.c:19:
tixGrid.h: In function ‘Tix_GrSelModify’:
tixGrid.h:388:25: note: in a call to function ‘Tix_GrAddChangedRect’
  388 | EXTERN void             Tix_GrAddChangedRect _ANSI_ARGS_((
      |                         ^~~~~~~~~~~~~~~~~~~~

Tix_GrMergeSelection() calls Tix_GrAddChangedRect with sbPtr->range which is of type int[2][2]. The function Tix_GrAddChangedRect() takes a parameter of type int[2][2]. These types seem to both be the same array of arrays, having a total length of 16, but apparently, the type is decaying to int(*)[2] somewhere, causing GCC to think the parameter is only 8 bytes instead of 16. sizeof(int) is 4 bytes, I think. GCC 11 gives -Wstringop-overflow when no string op is used links to GCC 11 bug report 101854 in a similar situation.

Turns out that -Wstringop-overflow is broken. Gcc bug 88443 has the entire list of -Wstringop-overflow bugs.

I am using Perl 5.41.2, installed with Perlbrew, inside the openSUSE Tumbleweed distro in WSL2.

Both the CPAN version of Perl/Tk and the latest GitHub version have the same warning.

VERSIONS

Perl 5.41.2 (installed from source with Perlbrew)
GCC 13.3.0 (official Tumbleweed package)
GLIBC 2.39 (official Tumbleweed package)
openSUSE Tumbleweed 20240725-0 (Last month's snapshot)
perl-Tk version: 804.036-18-gf0bb386b
WSL2 version:

WSL version: 2.2.4.0
Kernel version: 5.15.153.1-2
WSLg version: 1.0.61
MSRDC version: 1.2.5326
Direct3D version: 1.611.1-81528511
DXCore version: 10.0.26091.1-240325-1447.ge-release
Windows version: 10.0.19045.4780

perl -V

Summary of my perl5 (revision 5 version 41 subversion 2) configuration:

  Platform:
    osname=linux
    osvers=5.15.153.1-microsoft-standard-wsl2
    archname=x86_64-linux
    uname='linux msi 5.15.153.1-microsoft-standard-wsl2 #1 smp fri mar 29 23:14:13 utc 2024 x86_64 x86_64 x86_64 gnulinux '
    config_args='-de -Dprefix=/home/nathan/perl5/perlbrew/perls/perl-5.41.2 -Dusedevel -Aeval:scriptdir=/home/nathan/perl5/perlbrew/perls/perl-5.41.2/bin'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='cc'
    ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-O2'
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='13.3.0'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/x86_64-suse-linux/lib /usr/lib /usr/lib64 /usr/local/lib64
    libs=-lpthread -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -ldl -lm -lcrypt -lutil -lc
    libc=/lib/../lib64/libc.so.6
    so=so
    useshrplib=false
    libperl=libperl.a
    gnulibc_version='2.39'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl):
  Compile-time options:
    HAS_LONG_DOUBLE
    HAS_STRTOLD
    HAS_TIMES
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_HASH_FUNC_SIPHASH13
    PERL_HASH_USE_SBOX32
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_DEVEL
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
  Built under linux
  Compiled at Aug 20 2024 15:21:53
  %ENV:
    PERLBREW_HOME="/home/nathan/.perlbrew"
    PERLBREW_MANPATH="/home/nathan/perl5/perlbrew/perls/perl-5.41.2/man"
    PERLBREW_PATH="/home/nathan/perl5/perlbrew/bin:/home/nathan/perl5/perlbrew/perls/perl-5.41.2/bin"
    PERLBREW_PERL="perl-5.41.2"
    PERLBREW_ROOT="/home/nathan/perl5/perlbrew"
    PERLBREW_SHELLRC_VERSION="0.98"
    PERLBREW_VERSION="0.98"
  @INC:
    /home/nathan/perl5/perlbrew/perls/perl-5.41.2/lib/site_perl/5.41.2/x86_64-linux
    /home/nathan/perl5/perlbrew/perls/perl-5.41.2/lib/site_perl/5.41.2
    /home/nathan/perl5/perlbrew/perls/perl-5.41.2/lib/5.41.2/x86_64-linux
    /home/nathan/perl5/perlbrew/perls/perl-5.41.2/lib/5.41.2