Fix volantis boot.

NVIDIA binary blobs are assuming that __cache_clear, _Unwind_Backtrace,
and _Unwind_GetIP are all in some library that they link, but now we've
cleaned up this leakage, they're no longer getting it. Deliberately leak
the symbols from libc.so until we get new blobs.

Bug: http://b/20065774
Change-Id: I92ef07b2bce8d1ad719bf40dab41d745cd6904d4

libc/Android.mk

@@ -1384,7 +1384,8 @@ LOCAL_LDFLAGS := -Wl,--version-script,$(LOCAL_PATH)/version_script.txt
 # We'd really like to do this for all architectures, but since this wasn't done
 # before, these symbols must continue to be exported on LP32 for binary
 # compatibility.
-LOCAL_LDFLAGS_64 := -Wl,--exclude-libs,libgcc.a
+# TODO: disabled for http://b/20065774.
+#LOCAL_LDFLAGS_64 := -Wl,--exclude-libs,libgcc.a
 
 # TODO: This is to work around b/19059885. Remove after root cause is fixed
 LOCAL_LDFLAGS_arm := -Wl,--hash-style=sysv

libc/arch-arm64/arm64.mk

@@ -40,6 +40,8 @@ libc_bionic_src_files_arm64 += \
     arch-arm64/bionic/syscall.S \
     arch-arm64/bionic/vfork.S \
 
+# Work around for http://b/20065774.
+libc_bionic_src_files_arm64 += arch-arm64/bionic/libgcc_compat.c
 
 libc_crt_target_cflags_arm64 := \
     -I$(LOCAL_PATH)/arch-arm64/include

libc/arch-arm64/bionic/libgcc_compat.c

@@ -0,0 +1,11 @@
+/* STOPSHIP: remove this once the flounder blobs have been rebuilt (http://b/20065774). */
+
+extern void __clear_cache(char*, char*);
+extern char _Unwind_Backtrace;
+extern char _Unwind_GetIP;
+
+void* __bionic_libgcc_compat_symbols[] = {
+    &__clear_cache,
+    &_Unwind_Backtrace,
+    &_Unwind_GetIP,
+};

libc/version_script.txt

@@ -1,4 +1,9 @@
 LIBC {
+  global:
+    /* Work-around for http://b/20065774. */
+    __clear_cache;
+    _Unwind_Backtrace;
+    _Unwind_GetIP;
   local:
     _ZSt7nothrow;
     _ZdaPv;