Build fails with strict-aliasing violations #148
Description
I tried to build with the following *FLAGS to optimize the build: -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing
The -Werror=* flags are important to detect cases where the compiler can try to optimize based on assuming UB cannot happen, and miscompile code that has UB in it. strict-aliasing issues are always bad but LTO can make them even worse.
I got this error:
[4/5] /usr/bin/x86_64-pc-linux-gnu-g++ -DNDEBUG -DSTATIC_ANDROIDFW_FOR_TOOLS -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCE -D_LARGEFILE64_SOURCE -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1_build/vendor -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/include_pathutils -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/core/libcutils/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/logging/liblog/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/core/libsystem/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/core/libutils/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/libbase/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/native/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/libziparchive/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/incremental_delivery/incfs/util/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/fmtlib/include -pipe -march=native -fstack-protector-all -O2 -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Werror=lto-type-mismatch -Wformat -Werror=format-security -ftrivial-auto-var-init=zero -std=gnu++20 -Wno-attributes -MD -MT vendor/CMakeFiles/libandroidfw.dir/base/libs/androidfw/ResourceTypes.cpp.o -MF vendor/CMakeFiles/libandroidfw.dir/base/libs/androidfw/ResourceTypes.cpp.o.d -o vendor/CMakeFiles/libandroidfw.dir/base/libs/androidfw/ResourceTypes.cpp.o -c /var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/ResourceTypes.cpp
FAILED: vendor/CMakeFiles/libandroidfw.dir/base/libs/androidfw/ResourceTypes.cpp.o
/usr/bin/x86_64-pc-linux-gnu-g++ -DNDEBUG -DSTATIC_ANDROIDFW_FOR_TOOLS -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCE -D_LARGEFILE64_SOURCE -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1_build/vendor -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/include_pathutils -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/core/libcutils/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/logging/liblog/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/core/libsystem/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/core/libutils/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/libbase/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/native/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/libziparchive/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/incremental_delivery/incfs/util/include -I/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/fmtlib/include -pipe -march=native -fstack-protector-all -O2 -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Werror=lto-type-mismatch -Wformat -Werror=format-security -ftrivial-auto-var-init=zero -std=gnu++20 -Wno-attributes -MD -MT vendor/CMakeFiles/libandroidfw.dir/base/libs/androidfw/ResourceTypes.cpp.o -MF vendor/CMakeFiles/libandroidfw.dir/base/libs/androidfw/ResourceTypes.cpp.o.d -o vendor/CMakeFiles/libandroidfw.dir/base/libs/androidfw/ResourceTypes.cpp.o -c /var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/ResourceTypes.cpp
/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/ResourceTypes.cpp: In member function ‘int android::ResTable_config::diff(const android::ResTable_config&) const’:
/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/ResourceTypes.cpp:2234:52: warning: bitwise operation between different enumeration types ‘android::ResTable_config::<unnamed enum>’ and ‘android::ResTable_config::<unnamed enum>’ is deprecated [-Wdeprecated-enum-enum-conversion]
2234 | if (((inputFlags^o.inputFlags)&(MASK_KEYSHIDDEN|MASK_NAVHIDDEN)) != 0)
| ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/ResourceTypes.cpp: In static member function ‘static bool android::ResTable::stringToFloat(const char16_t*, size_t, android::Res_value*)’:
/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/ResourceTypes.cpp:5588:14: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
5588 | *(float*)(&outValue->data) = f;
| ^~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/ResourceTypes.cpp: In member function ‘void android::ResTable::print_value(const Package*, const android::Res_value&) const’:
/var/tmp/portage/dev-util/android-tools-35.0.1/work/android-tools-35.0.1/vendor/base/libs/androidfw/ResourceTypes.cpp:7619:33: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
7619 | printf("(float) %g\n", *(const float*)&value.data);
| ^~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
Attached is a full build log. There are other errors too.
build.log
There's a tracking issue downstream at https://bugs.gentoo.org/858311
...
Okay, so now you may ask, why am I reporting an error in Android source code to this wrapper project? Good question.
The answer is that I have looked everywhere in the codebase and I cannot tell where the libandroidfw target is ever used. It was added in commit be1a63d but that commit never made use of it. Helpfully, the commit message is highly detailed and explains the whys and wherefores of why it was added:
commit be1a63d3986257b53c7482e5deb3837f140382ee
Author: Đoàn Trần Công Danh <congdanhqx@gmail.com>
AuthorDate: Tue Nov 10 09:13:23 2020
Commit: Đoàn Trần Công Danh <congdanhqx@gmail.com>
CommitDate: Tue Nov 10 09:53:38 2020
vendor: add libandroidfw
It is never mentioned in build.ninja other than as part of the default "all" target. Using a sed to delete:
vendor/CMakeLists.txt:include(CMakeLists.libandroidfw.txt)
results in android-tools building and installing correctly (without LTO, anyway). So my assumption is that by dropping this unused dependency, google's source code bugs become "not our problem". Also ~25 fewer build edges means faster builds -- and 16mb less unpacked source code size (did not measure effects on compressed tarballs).