mir: build failure on s390x

[Gianfranco Costamagna]

Hello, looks like we are missing one "+1" from somewhere, but I don't have enough knowledge on this code... can you please have a look? in the meanwhile I'm probably going to disable that error

cd /<<PKGBUILDDIR>>/build-s390x/src/miral && /usr/bin/cc -DBOOST_ALL_NO_LIB -DBOOST_DATE_TIME_DYN_LINK -DBOOST_FILESYSTEM_DYN_LINK -DBOOST_IOSTREAMS_DYN_LINK -DBOOST_PROGRAM_OPTIONS_DYN_LINK -DBOOST_SYSTEM_DYN_LINK -DEGL_NO_X11 -DLOG_NDEBUG=1 -DLTTNG_UST_HAVE_SDT_INTEGRATION -DMESA_EGL_NO_X11_HEADERS -DMIR_DRMMODEADDFB_HAS_CONST_SIGNATURE -DMIR_LOG_COMPONENT_FALLBACK=\"miral\" -DMIR_SERVER_EGL_OPENGL_API=EGL_OPENGL_ES_API -DMIR_SERVER_EGL_OPENGL_BIT=EGL_OPENGL_ES2_BIT -DMIR_SERVER_GLEXT_H="<GLES2/gl2ext.h>" -DMIR_SERVER_GL_H="<GLES2/gl2.h>" -DMIR_VERSION_MAJOR=1 -DMIR_VERSION_MICRO=1 -DMIR_VERSION_MINOR=7 -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCE -D_GNU_SOURCE -I/<<PKGBUILDDIR>>/include/core -I/<<PKGBUILDDIR>>/include/common -I/<<PKGBUILDDIR>>/include/cookie -I/<<PKGBUILDDIR>>/src/include/common -I/<<PKGBUILDDIR>>/build-s390x/src/capnproto -I/<<PKGBUILDDIR>>/build-s390x/src/protobuf -I/<<PKGBUILDDIR>>/include/platform -I/<<PKGBUILDDIR>>/include/client -I/<<PKGBUILDDIR>>/include/server -I/<<PKGBUILDDIR>>/src/include/platform -I/<<PKGBUILDDIR>>/include/miral -I/usr/include/uuid -I/<<PKGBUILDDIR>>/include/wayland -I/<<PKGBUILDDIR>>/src/wayland/generated -g -O2 -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -pthread -g -Wall -pedantic -Wextra -fPIC -Werror -flto -ffat-lto-objects -fvisibility=hidden -pthread -o CMakeFiles/miral-internal.dir/xcursor.c.o -c /<<PKGBUILDDIR>>/src/miral/xcursor.c
In file included from /usr/include/string.h:495,
                 from /<<PKGBUILDDIR>>/src/miral/xcursor.c:26:
In function ‘strncpy’,
    inlined from ‘_XcursorAddPathElt’ at /<<PKGBUILDDIR>>/src/miral/xcursor.c:647:5,
    inlined from ‘_XcursorBuildFullname’ at /<<PKGBUILDDIR>>/src/miral/xcursor.c:726:5,
    inlined from ‘xcursor_load_theme’ at /<<PKGBUILDDIR>>/src/miral/xcursor.c:875:10:
/usr/include/s390x-linux-gnu/bits/string_fortified.h:106:10: error: ‘strncpy’ output truncated before terminating nul copying 7 bytes from a string of the same length [-Werror=stringop-truncation]
  106 | return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In function ‘strncpy’,
    inlined from ‘_XcursorAddPathElt’ at /<<PKGBUILDDIR>>/src/miral/xcursor.c:647:5,
    inlined from ‘_XcursorBuildFullname’ at /<<PKGBUILDDIR>>/src/miral/xcursor.c:727:5,
    inlined from ‘xcursor_load_theme’ at /<<PKGBUILDDIR>>/src/miral/xcursor.c:884:11:
/usr/include/s390x-linux-gnu/bits/string_fortified.h:106:10: error: ‘strncpy’ output truncated before terminating nul copying 11 bytes from a string of the same length [-Werror=stringop-truncation]
  106 | return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[3]: *** [src/miral/CMakeFiles/miral-internal.dir/build.make:183: src/miral/CMakeFiles/miral-internal.dir/xcursor.c.o] Error 1
make[3]: *** Waiting for unfinished jobs....

[Alan Griffiths (alan-griffiths)]

Looking at the code, it is written correctly and handles the case where strncpy() "truncates before the terminating nul". It is unfortunate that this triggers a warning.

[Gianfranco Costamagna (costamagnagianfranco)]

Yep, I created a minimal test case on my laptop, and couldn't figure out why there was this warning in first place.
At the end, I ended up in something like this:
http://launchpadlibrarian.net/490452795/mir_1.7.1-0ubuntu6_1.7.1-0ubuntu7.diff.gz

[Gianfranco Costamagna (costamagnagianfranco)]

I'm not closing this bug, because overriding the build flag is not a fix...

[Chris Halse Rogers (raof)]

While it's true this won't result in an unterminated char*, I think (but am not sure) that it *is* a logic bug. Because it will be truncating the string by overwriting the final (non-null) character with null?

[Gianfranco Costamagna (costamagnagianfranco)]

@raof this is probably true if the path is long, but I can't figure out how to patch it...

[Alan Griffiths (alan-griffiths)]

In src/miral/CMakeLists.txt

Change:

    set_source_files_properties(xcursor.c PROPERTIES COMPILE_DEFINITIONS _GNU_SOURCE)

to

    set_source_files_properties(xcursor.c PROPERTIES
        COMPILE_DEFINITIONS _GNU_SOURCE
        COMPILE_FLAGS "-Wno-error=stringop-truncation"
    )

[Launchpad Janitor (janitor)]

This bug was fixed in the package mir - 2.2.0-0ubuntu2

---------------
mir (2.2.0-0ubuntu2) hirsute; urgency=medium

  * debian/patches/disable-stringop-truncation.patch:
    - Disable -Werror=stringop-truncation on imported xcursor.c file. This
      trggers on s390x (and only s390x?), but the code appears safe.
      Fixes FTBFS on s390x (LP: #1889166)
  * debian/patches/increase-display-test-timeout.patch:
    - Standardise test timeouts to 60s (increased from 10s) in the
      DisplayConfiguratonTest acceptance tests. These inconsistently fail on
      the Launchpad builders on slow architectures (notably arm64 and armhf).

 -- Christopher James Halse Rogers <email address hidden> Thu, 17 Dec 2020 10:44:50 +1100