sanitizer_common: Try looking up symbols with RTLD_DEFAULT if RTLD_NEXT does not work.

[pcc]

Summary

If the lookup using RTLD_NEXT failed, the sanitizer runtime library
is later in the library search order than the DSO that we are trying
to intercept, which means that we cannot intercept this function. We
still want the address of the real definition, though, so look it up
using RTLD_DEFAULT.

[pcc]

I cannot run the test on Android myself, so it may require adjustment.

[pcc]

• Fix test case

compiler-rt/lib/interception/interception_linux.cc

 namespace __interception {
 bool GetRealFunctionAddress(const char *func_name, uptr *func_addr,
     uptr real, uptr wrapper) {
 #ifdef __NetBSD__
   // XXX: Find a better way to handle renames
   if (internal_strcmp(func_name, "sigaction") == 0) func_name = "__sigaction14";
 #endif
   *func_addr = (uptr)dlsym(RTLD_NEXT, func_name);
+  if (!*func_addr) {
+    // If the lookup using RTLD_NEXT failed, the sanitizer runtime library is
+    // later in the library search order than the DSO that we are trying to
+    // intercept, which means that we cannot intercept this function. We still
+    // want the address of the real definition, though, so look it up using
+    // RTLD_DEFAULT.
+    *func_addr = (uptr)dlsym(RTLD_DEFAULT, func_name);
+  }
   return real == wrapper;
 }
 
 #if !defined(__ANDROID__)  // android does not have dlvsym
 void *GetFuncAddrVer(const char *func_name, const char *ver) {
   return dlvsym(RTLD_NEXT, func_name, ver);
 }
 #endif  // !defined(__ANDROID__)
 
 }  // namespace __interception
 
 #endif  // __linux__ || __FreeBSD__ || __NetBSD__

compiler-rt/test/ubsan/TestCases/Misc/Inputs/no-interception-dso.c

+int dso_function(int i) {
+  return i + 1;
+}

compiler-rt/test/ubsan/TestCases/Misc/no-interception.cpp

+// REQUIRES: android
+
+// Tests that ubsan can detect errors on Android if libc appears before the
+// runtime in the library search order, which means that we cannot intercept
+// symbols.
+
+// RUN: %clangxx %p/Inputs/no-interception-dso.c -fsanitize=undefined -fPIC -shared -o %dynamiclib %ld_flags_rpath_so
+
+// Make sure that libc is first in DT_NEEDED.
+// RUN: %clangxx %s -lc -o %t %ld_flags_rpath_exe
+// RUN: %run %t 2>&1 | FileCheck %s
+
+#include <limits.h>
+
+int dso_function(int);
+
+int main(int argc, char **argv) {
+  // CHECK: signed integer overflow
+  dso_function(INT_MAX);
+}

compiler-rt/test/ubsan/lit.common.cfg

 # Default test suffixes.
 config.suffixes = ['.c', '.cc', '.cpp']
 
 # Check that the host supports UndefinedBehaviorSanitizer tests
 if config.host_os not in ['Linux', 'Darwin', 'FreeBSD', 'Windows', 'NetBSD']:
   config.unsupported = True
 
 config.available_features.add('arch=' + config.target_arch)
+
+config.excludes = ['Inputs']