Hide unwinder symbols on all architectures.

Test: readelf
Bug: android/ndk#1166
Change-Id: I28b64492e5a66a66608874133ddd955ea2f53d7f

build/cmake/android.toolchain.cmake

@@ -347,6 +347,13 @@ if(ANDROID_LD STREQUAL lld)
 endif()
 
 # Don't re-export libgcc symbols in every binary.
+list(APPEND ANDROID_LINKER_FLAGS -Wl,--exclude-libs,libgcc.a)
+# arm32 currently uses a linker script in place of libgcc to ensure that
+# libunwind is linked in the correct order. --exclude-libs does not propagate to
+# the contents of the linker script and can't be specified within the linker
+# script. Hide both regardless of architecture to future-proof us in case we
+# move other architectures to a linker script (which we may want to do so we
+# automatically link libclangrt on other architectures).
 list(APPEND ANDROID_LINKER_FLAGS -Wl,--exclude-libs,libgcc_real.a)
 list(APPEND ANDROID_LINKER_FLAGS -Wl,--exclude-libs,libatomic.a)
 

build/core/default-build-commands.mk

@@ -84,7 +84,13 @@ endef
 
 cmd-strip = $(PRIVATE_STRIP) $(PRIVATE_STRIP_MODE) $(call host-path,$1)
 
-TARGET_LIBGCC = -lgcc -Wl,--exclude-libs,libgcc_real.a
+# arm32 currently uses a linker script in place of libgcc to ensure that
+# libunwind is linked in the correct order. --exclude-libs does not propagate to
+# the contents of the linker script and can't be specified within the linker
+# script. Hide both regardless of architecture to future-proof us in case we
+# move other architectures to a linker script (which we may want to do so we
+# automatically link libclangrt on other architectures).
+TARGET_LIBGCC = -lgcc -Wl,--exclude-libs,libgcc.a -Wl,--exclude-libs,libgcc_real.a
 TARGET_LIBATOMIC = -latomic -Wl,--exclude-libs,libatomic.a
 TARGET_LDLIBS := -lc -lm
 

docs/BuildSystemMaintainers.md

@@ -410,10 +410,11 @@ preserved. By default, only symbols in used sections will be included in the
 linked binary.
 
 If this behavior is not desired for your build system, ensure that these flags
-are at least used for `libgcc_real.a` (`libgcc.a` is a linker script, and
-`--exclude-libs` does not have any effect on the contents of linker scripts) and
-`libunwind.a` (libunwind is only used for ARM32). This is necessary to avoid
-unwinding bugs on ARM32. See [Unwinding] for more information.
+are at least used for `libgcc.a` (`libgcc_real.a` on Arm32, where `libgcc.a` is
+a linker script, as `--exclude-libs` does not have any effect on the contents of
+linker scripts) and `libunwind.a` (libunwind is only used for ARM32). This is
+necessary to avoid unwinding bugs on Arm32. See [Unwinding] for more
+information.
 
 [visibility]: https://gcc.gnu.org/wiki/Visibility
 
@@ -513,9 +514,12 @@ these symbols from a shared library. If this library was built with the wrong
 unwinder, it is possible for one unwinder to call into the other. As they are
 not compatible, this will likely result in either a crash or a failed unwind. To
 avoid this problem, libraries should always be built with
-`-Wl,--exclude-libs,libgcc_real.a` and `-Wl,--exclude-libs,libunwind.a` (the
-latter is only necessary for 32-bit ARM) to ensure that unwind symbols are not
-re-exported from shared libraries.
+`-Wl,--exclude-libs,libgcc.a`, `-Wl,--exclude-libs,libgcc_real.a` and
+`-Wl,--exclude-libs,libunwind.a` (the latter is only necessary for 32-bit Arm)
+to ensure that unwind symbols are not re-exported from shared libraries. Note
+that `libgcc_real.a` is needed because on some architectures (currently only
+32-bit Arm) `libgcc.a` is a linker script and `--exclude-libs` does not extend
+to the contents of linker scripts.
 
 Even with the above precautions, it is still possible for an improperly built
 external dependency to provide an incorrect unwind implementation as described

docs/changelogs/Changelog-r21.md

@@ -61,6 +61,9 @@ For Android Studio issues, follow the docs on the [Android Studio site].
    Pure C/C++ executables were fine, but this effectively broke all app
    debugging. The error from gdb that confirms you were affected by this was
    `gdb-8.3/gdb/psymtab.c:316: internal-error: sect_index_text not initialized`.
+ * [Issue 1166]: Rehid unwinder symbols all architectures.
+
+[Issue 1166]: https://github.com/android/ndk/issues/1166
 
 ## Changes