-fsanitize=cfi requires LTO. Normally, the Clang driver automatically
enables emutls, but it's broken with -flto, so work around it by passing
-Wl,-plugin-opt=-emulated-tls.
See https://buganizer.corp.google.com/issues/72706604#comment15
Enable the workaround with ctx.Device(), which is the same condition used
in the existing I18acac41aac885fc6635fbd55f96ba7c845eb5e7 workaround.
Bug: b/72706604
Bug: https://github.com/android-ndk/ndk/issues/498
Test: m libaudioflinger (on internal master); \
readelf -sW symbols/system/lib64/libaudioflinger.so | grep tlNBLogWriter
check that __emutls_t.tlNBLogWriter exists
check that no symbols of type TLS exist
Change-Id: I2cf65574c52476843cc017ee176a7d6777e2ce0b
Allow developers to disable LTO to reduce build time.
Test: m checkbuild
Test: DISABLE_LTO=true m checkbuild
Bug: 62839002
Change-Id: I30642e3cfff60c4874a2f8797d08105b4e07cc6d
Propagation of LTO flags from a main binary or library to its static
dependencies is necessary so that objects being linked with LTO are built as
bitcode rather than native objects. This propagation was broken when thin LTO
was added to the build system. This patch propagates the LTO mode (thin or full)
down to object and archive dependencies.
Test: Build libhwui with full and thin LTO and check that intermediate objects
are LLVM bitcode.
Change-Id: Ic57a80d75052d86940db076fbc0f5375a79c89a1
Also adds checks that the dependencies are android.Modules and
are not disabled.
Test: m checkbuild
Change-Id: I05e945f38915d49cd3c0ab72a86576949bc7eff2
ThinLTO achieves comparable performance to full LTO while taking much
less time for compilation.
Test: Build hwui with "thin" and "full" LTO
Change-Id: If3400b82af0d5e0226410c8b740999cdad746a59
In LTO mode the backend constructs a target exclusively from command line flags,
without opportunity to accept code gen arguments from Clang. Clang does not
currently pass the -emulated-tls parameter for Android, even though it defaults
to emulated TLS for Android in non-LTO builds. Until this is fixed upstream, we
can explicitly specify that the LTO output for Android should use emulated TLS.
Test: build libandroid with LTO, verified that it uses __emutls_get_address
rather than __tls_get_addr.
Change-Id: I18acac41aac885fc6635fbd55f96ba7c845eb5e7
Enabling the lto property for a module builds that module and all static
dependencies with LTO.
LTO (link-time optimization) allows the compiler to optimize and
generate code for the entire module at link time, rather than
per-compilation unit. LTO is required for Clang CFI and other
whole-program optimization techniques. LTO also allows cross-compilation
unit optimizations that should result in faster and smaller code, at the
expense of additional compilation time.
Test: make -j12 libc with lto: true for libc
Change-Id: Ib8baefedf60e02701d44673a7c473e0845730101
