Test compilation failures on GCC 11: error: array subscript -1 is outside array bounds of 'char[6]' [-Werror=array-bounds]

[sanjayankur31]

Hi there,

While packaging the 0.38.0 release for Fedora, we're seeing the build fail when tests are enabled. (This is on Fedora 34 and 35, which are both using GCC 11 now). The failures are of this form:

[ 32%] Building CXX object test/CMakeFiles/gsl-lite-v1-no-exc-cpp11.t.dir/owner.t.cpp.o
cd /builddir/build/BUILD/gsl-lite-0.38.0/x86_64-redhat-linux-gnu/test && /usr/bin/g++ -Dgsl_CONFIG_CONTRACT_CHECKING_AUDIT -Dgsl_CONFIG_CONTRACT_VIOLATION_TERMINATES -Dgsl_C
ONFIG_DEFAULTS_VERSION=1 -Dgsl_CONFIG_UNENFORCED_CONTRACTS_ELIDE -Dgsl_TESTING_ -I/builddir/build/BUILD/gsl-lite-0.38.0/include -O2 -flto=auto -ffat-lto-objects -fexceptions
 -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protec
tor-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1  -m64  -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -Werror -Wall -Wextra -W
conversion -Wsign-conversion -fno-elide-constructors -fstrict-aliasing -Wstrict-aliasing=2 -pedantic -Wno-long-long -fno-exceptions -std=c++11 -Winvalid-pch -include /buildd
ir/build/BUILD/gsl-lite-0.38.0/x86_64-redhat-linux-gnu/test/CMakeFiles/gsl-lite-v1-no-exc-cpp11.t.dir/cmake_pch.hxx -o CMakeFiles/gsl-lite-v1-no-exc-cpp11.t.dir/owner.t.cpp.
o -c /builddir/build/BUILD/gsl-lite-0.38.0/test/owner.t.cpp                                                                                                                  
/builddir/build/BUILD/gsl-lite-0.38.0/test/string_span.t.cpp: In function '__lest_function__883(lest::env&)':
/builddir/build/BUILD/gsl-lite-0.38.0/test/string_span.t.cpp:889:11: error: array subscript -1 is outside array bounds of 'char[6]' [-Werror=array-bounds]
  889 |     a.back() = '2';                                                                                                                                                  
      |     ~~~~~~^~                       
/builddir/build/BUILD/gsl-lite-0.38.0/test/string_span.t.cpp:885:10: note: while referencing 'hello'
  885 |     char hello[] = "hello";                                                                                                                                          
      |          ^~~~~                                                                                        
...

The complete build log is here: gsl-lite-0.38.0-buildlog.txt

[sanjayankur31]

I'm seeing similar errors on Fedora 33 which is on GCC 10, so this may not be a GCC related issue. Build log for GCC 10 build:
gsl-lite-0.38.0-buildlog-f33-gcc10.txt

[mbeutel]

Thanks for the report.

This appears to be a compiler bug which first surfaced in GCC 10.3. Here's a minimal repro:
https://gcc.godbolt.org/z/4xaY9vfzW

The problem only occurs when "-O2" or higher is enabled, hence it doesn't appear in our CI because we only test with the Debug build configuration (to keep the overall build times low). I'll change that so at least one version of each compiler will also build the RelWithDebInfo configuration.

I'll issue a bug report with GCC.

[sanjayankur31]

Thanks very much. If there's anything we can do to help with this, please do let us know.

[mbeutel]

Bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100137

For the time being, you can make your build work by adding -Wno-error=array-bounds to CXXFLAGS (or -Wno-array-bounds if you want to suppress the warning entirely).

[sanjayankur31]

Thanks, I've added that to our build now.

Fedora currently builds for a number of architectures:

https://fedoraproject.org/wiki/Architectures

• x86_64
• i686
• aarch64
• ppc64le
• armv7hl
• s390x

I'm happy to report that it builds correctly and all tests pass on all architectures apart from s390x. I've filed a separate issue for that here: #304

Here are the test builds:

• Fedora 35/rawhide (GCC 11.0.1): https://koji.fedoraproject.org/koji/taskinfo?taskID=66241363
• Fedora 34 (GCC 11.0.1): https://koji.fedoraproject.org/koji/taskinfo?taskID=66242324
• Fedora 33 (GCC 10.2.1): https://koji.fedoraproject.org/koji/taskinfo?taskID=66242329

[mbeutel]

Awesome, thanks.

I hope I can fix #304 and add the -Wno-error=array-bounds workaround to the test suite later this week. I'll then issue a bugfix release which also includes the fix to #302.

[mbeutel]

RelWithDebInfo CI builds added in f5b5b93, so as expected the build now failed for GCC 10. Added error suppression in subsequent commit 2ad316d.