Break libdl.so and ld-android.so's dependency on libc.so.

 * Specify "nocrt: true" to avoid calling __cxa_finalize.

 * Define a dummy __aeabi_unwind_cpp_pr0 for arm32.

Bug: b/62815515
Bug: b/73873002
Test: boot AOSP hikey960-userdebug
Test: run ndk_cxa_example in special /system/bin/debug namespace
Test: run Bionic unit tests
Change-Id: I59bcb100a2753286b59c51a47d7a183507219a07
(cherry picked from commit 470b66644b912ac3025ea30141f2f327bb879445)

5 files changed, 35 insertions, 18 deletions

diff --git a/libdl/Android.bp b/libdl/Android.bp
index 082cdead1..5998f9bbc 100644
--- a/libdl/Android.bp
+++ b/libdl/Android.bp
@@ -84,12 +84,7 @@ cc_library {
     ],
     stl: "none",
 
-    // NOTE: libdl needs __aeabi_unwind_cpp_pr0 from libgcc.a but libgcc.a needs a
-    // few symbols from libc. Using --no-undefined here results in having to link
-    // against libc creating a circular dependency which is removed and we end up
-    // with missing symbols. Since this library is just a bunch of stubs, we set
-    // LOCAL_ALLOW_UNDEFINED_SYMBOLS to remove --no-undefined from the linker flags.
-    allow_undefined_symbols: true,
+    nocrt: true,
     system_shared_libs: [],
 
     // This is placeholder library the actual implementation is (currently)
diff --git a/libdl/libdl.cpp b/libdl/libdl.cpp
index c8340888e..402804ec5 100644
--- a/libdl/libdl.cpp
+++ b/libdl/libdl.cpp
@@ -214,4 +214,16 @@ struct android_namespace_t* android_get_exported_namespace(const char* name) {
   return __loader_android_get_exported_namespace(name);
 }
 
+#if defined(__arm__)
+// An arm32 unwinding table has an R_ARM_NONE relocation to
+// __aeabi_unwind_cpp_pr0. This shared library will never invoke the unwinder,
+// so it doesn't actually need the routine. Define a dummy version here,
+// because the real version calls libc functions (e.g. memcpy, abort), which
+// would create a dependency cycle with libc.so.
+__attribute__((visibility("hidden")))
+void __aeabi_unwind_cpp_pr0() {
+  __builtin_trap();
+}
+#endif
+
 } // extern "C"
diff --git a/linker/Android.bp b/linker/Android.bp
index 2fcf369ef..7877a372d 100644
--- a/linker/Android.bp
+++ b/linker/Android.bp
@@ -271,12 +271,7 @@ cc_library {
     name: "ld-android",
     defaults: ["linux_bionic_supported"],
 
-    // NOTE: ld-android.so needs __aeabi_unwind_cpp_pr0 from libgcc.a but libgcc.a
-    // needs a few symbols from libc. Using --no-undefined here results in having to
-    // link against libc creating a circular dependency which is removed and we end
-    // up with missing symbols. Since this library is just a bunch of stubs, we set
-    // allow_undefined_symbols to remove --no-undefined from the linker flags.
-    allow_undefined_symbols: true,
+    nocrt: true,
     system_shared_libs: [],
 
     sanitize: {
diff --git a/linker/ld_android.cpp b/linker/ld_android.cpp
index e2499b300..0528cd889 100644
--- a/linker/ld_android.cpp
+++ b/linker/ld_android.cpp
@@ -26,11 +26,10 @@
  * SUCH DAMAGE.
  */
 
-#include <stdlib.h>
 #include <sys/cdefs.h>
 
 extern "C" void __internal_linker_error() {
-  abort();
+  __builtin_trap();
 }
 
 __strong_alias(__loader_android_create_namespace, __internal_linker_error);
@@ -59,3 +58,14 @@ __strong_alias(__loader_dl_unwind_find_exidx, __internal_linker_error);
 #endif
 __strong_alias(rtld_db_dlactivity, __internal_linker_error);
 
+#if defined(__arm__)
+// An arm32 unwinding table has an R_ARM_NONE relocation to
+// __aeabi_unwind_cpp_pr0. This shared library will never invoke the unwinder,
+// so it doesn't actually need the routine. Define a dummy version here,
+// because the real version calls libc functions (e.g. memcpy, abort), which
+// would create a dependency cycle with libc.so.
+__attribute__((visibility("hidden")))
+extern "C" void __aeabi_unwind_cpp_pr0() {
+  __builtin_trap();
+}
+#endif
diff --git a/tests/dlfcn_test.cpp b/tests/dlfcn_test.cpp
index 84f525dee..7d9abf926 100644
--- a/tests/dlfcn_test.cpp
+++ b/tests/dlfcn_test.cpp
@@ -1438,7 +1438,8 @@ const llvm::ELF::Elf32_Dyn* to_dynamic_table(const char* p) {
 #define DT_ANDROID_RELA (llvm::ELF::DT_LOOS + 4)
 
 template<typename ELFT>
-void validate_compatibility_of_native_library(const std::string& path, ELFT* elf) {
+void validate_compatibility_of_native_library(const std::string& soname,
+                                              const std::string& path, ELFT* elf) {
   bool has_elf_hash = false;
   bool has_android_rel = false;
   bool has_rel = false;
@@ -1464,10 +1465,14 @@ void validate_compatibility_of_native_library(const std::string& path, ELFT* elf
 
   ASSERT_TRUE(has_elf_hash) << path.c_str() << ": missing elf hash (DT_HASH)";
   ASSERT_TRUE(!has_android_rel) << path.c_str() << ": has packed relocations";
-  ASSERT_TRUE(has_rel) << path.c_str() << ": missing DT_REL/DT_RELA";
+  // libdl.so is simple enough that it might not have any relocations, so
+  // exempt it from the DT_REL/DT_RELA check.
+  if (soname != "libdl.so") {
+    ASSERT_TRUE(has_rel) << path.c_str() << ": missing DT_REL/DT_RELA";
+  }
 }
 
-void validate_compatibility_of_native_library(const char* soname) {
+void validate_compatibility_of_native_library(const std::string& soname) {
   // On the systems with emulation system libraries would be of different
   // architecture.  Try to use alternate paths first.
   std::string path = std::string(ALTERNATE_PATH_TO_SYSTEM_LIB) + soname;
@@ -1487,7 +1492,7 @@ void validate_compatibility_of_native_library(const char* soname) {
 
   ASSERT_TRUE(elf != nullptr);
 
-  validate_compatibility_of_native_library(path, elf);
+  validate_compatibility_of_native_library(soname, path, elf);
 }
 
 // This is a test for app compatibility workaround for arm apps