[compiler-rt] Remove explicit Android libatomic linking

[smeenai]

Summary

The comments date back to NDK r10, which is ancient. libatomic isn't
always needed anymore, and even when it is, it's bundled into
compiler-rt in the NDK so we'll get it automatically. Remove the
unnecessary explicit links.

[vitalybuka]

Not sure which one, but one of your patches breaks https://lab.llvm.org/buildbot/#/builders/77/builds/30001

[smeenai]

In D158793#4623992, @vitalybuka wrote:

Not sure which one, but one of your patches breaks https://lab.llvm.org/buildbot/#/builders/77/builds/30001

Thanks for the heads up. I'm pretty sure it's D158792, specifically the part that defaults compiler-rt to using the builtins library. I reverted it for now and I'm monitoring the bot.

[smeenai]

It's not urgent, but I'd like to reland that patch eventually though, since it reflects modern Android defaults. Looking at the buildbot Android scripts, I had a few questions:

• They're using NDK r21, which is unsupported. Are there any plans to upgrade to r23 or newer, since that would get us a fully LLVM-based toolchain and is what the Clang driver's Android defaults reflect now?
• It seems like they're building compiler-rt without the builtins. Would you be open to doing a builtins build before the compiler-rt build (which also mirrors how the LLVM runtimes build works)? It should be pretty quick to do so.

I'm happy to take a crack at both of those changes myself, but I'd need a way to eventually test on the buildbots to make sure things work.

[vitalybuka]

In D158793#4625767, @smeenai wrote:

It's not urgent, but I'd like to reland that patch eventually though, since it reflects modern Android defaults. Looking at the buildbot Android scripts, I had a few questions:

• They're using NDK r21, which is unsupported. Are there any plans to upgrade to r23 or newer, since that would get us a fully LLVM-based toolchain and is what the Clang driver's Android defaults reflect now?
• It seems like they're building compiler-rt without the builtins. Would you be open to doing a builtins build before the compiler-rt build (which also mirrors how the LLVM runtimes build works)? It should be pretty quick to do so.

I'm happy to take a crack at both of those changes myself, but I'd need a way to eventually test on the buildbots to make sure things work.

Thanks. That could be very helpful.
That script should run on usual Debian distro, and it try to run tests on anything it can see on ADB. So you can start with that.
I unlikely have a way to provide access to that bot to you, but that bot is relatively fast. So I can try patches for you, but also we can just land/revert them as needed.

compiler-rt/lib/asan/tests/CMakeLists.txt

set(ASAN_UNITTEST_INSTRUMENTED_LINK_FLAGS
   ${ASAN_UNITTEST_COMMON_LINK_FLAGS})
 list(APPEND ASAN_UNITTEST_INSTRUMENTED_LINK_FLAGS -fsanitize=address)
 
 set(ASAN_DYNAMIC_UNITTEST_INSTRUMENTED_LINK_FLAGS
   ${ASAN_UNITTEST_INSTRUMENTED_LINK_FLAGS}
   -shared-libasan)
 
 set(ASAN_UNITTEST_INSTRUMENTED_LIBS)
-# NDK r10 requires -latomic almost always.
-append_list_if(ANDROID atomic ASAN_UNITTEST_INSTRUMENTED_LIBS)
 
 set(ASAN_UNITTEST_NOINST_LINK_FLAGS ${ASAN_UNITTEST_COMMON_LINK_FLAGS})
 if(NOT APPLE)
   append_list_if(COMPILER_RT_HAS_LIBM -lm ASAN_UNITTEST_NOINST_LINK_FLAGS)
   append_list_if(COMPILER_RT_HAS_LIBDL -ldl ASAN_UNITTEST_NOINST_LINK_FLAGS)
   append_list_if(COMPILER_RT_HAS_LIBRT -lrt ASAN_UNITTEST_NOINST_LINK_FLAGS)
   append_list_if(COMPILER_RT_HAS_LIBPTHREAD -pthread ASAN_UNITTEST_NOINST_LINK_FLAGS)
   append_list_if(COMPILER_RT_HAS_LIBPTHREAD -pthread ASAN_DYNAMIC_UNITTEST_INSTRUMENTED_LINK_FLAGS)
 endif()
 
 # TODO(eugenis): move all -l flags above to _LIBS?
 set(ASAN_UNITTEST_NOINST_LIBS)
 append_list_if(COMPILER_RT_HAS_LIBLOG log ASAN_UNITTEST_NOINST_LIBS)
-# NDK r10 requires -latomic almost always.
-append_list_if(ANDROID atomic ASAN_UNITTEST_NOINST_LIBS)
 
 # Main AddressSanitizer unit tests.
 add_custom_target(AsanUnitTests)
 set_target_properties(AsanUnitTests PROPERTIES FOLDER "Compiler-RT Tests")
 
 # AddressSanitizer unit tests with dynamic runtime (on platforms where it's
 # not the default).
 add_custom_target(AsanDynamicUnitTests)

compiler-rt/lib/interception/tests/CMakeLists.txt

 endif()
 
 if(ANDROID)
   list(APPEND INTERCEPTION_TEST_LINK_FLAGS_COMMON -pie)
 endif()
 
 set(INTERCEPTION_TEST_LINK_LIBS)
 append_list_if(COMPILER_RT_HAS_LIBLOG log INTERCEPTION_TEST_LINK_LIBS)
-# NDK r10 requires -latomic almost always.
-append_list_if(ANDROID atomic INTERCEPTION_TEST_LINK_LIBS)
 
 append_list_if(COMPILER_RT_HAS_LIBDL -ldl INTERCEPTION_TEST_LINK_FLAGS_COMMON)
 append_list_if(COMPILER_RT_HAS_LIBRT -lrt INTERCEPTION_TEST_LINK_FLAGS_COMMON)
 append_list_if(COMPILER_RT_HAS_LIBPTHREAD -pthread INTERCEPTION_TEST_LINK_FLAGS_COMMON)
 # x86_64 FreeBSD 9.2 additionally requires libc++ to build the tests. Also,
 # 'libm' shall be specified explicitly to build i386 tests.
 if(CMAKE_SYSTEM MATCHES "FreeBSD-9.2-RELEASE")
   list(APPEND INTERCEPTION_TEST_LINK_FLAGS_COMMON "-lc++ -lm")

compiler-rt/lib/sanitizer_common/tests/CMakeLists.txt

 if(MSVC)
   list(APPEND SANITIZER_TEST_LINK_FLAGS_COMMON -Wl,/STACK:0xC00000)
 elseif (MINGW)
   list(APPEND SANITIZER_TEST_LINK_FLAGS_COMMON -Wl,--stack=0xC00000)
 endif()
 
 set(SANITIZER_TEST_LINK_LIBS)
 append_list_if(COMPILER_RT_HAS_LIBLOG log SANITIZER_TEST_LINK_LIBS)
-# NDK r10 requires -latomic almost always.
-append_list_if(ANDROID atomic SANITIZER_TEST_LINK_LIBS)
 
 append_list_if(COMPILER_RT_HAS_LIBDL -ldl SANITIZER_TEST_LINK_FLAGS_COMMON)
 append_list_if(COMPILER_RT_HAS_LIBRT -lrt SANITIZER_TEST_LINK_FLAGS_COMMON)
 append_list_if(COMPILER_RT_HAS_LIBPTHREAD -pthread SANITIZER_TEST_LINK_FLAGS_COMMON)
 # x86_64 FreeBSD 9.2 additionally requires libc++ to build the tests. Also,
 # 'libm' shall be specified explicitly to build i386 tests.
 if(CMAKE_SYSTEM MATCHES "FreeBSD-9.2-RELEASE")
   list(APPEND SANITIZER_TEST_LINK_FLAGS_COMMON "-lc++ -lm")