[ubsan-minimal] Get rid of the libc++ dependency.

[eugenis]

Summary

Use -nodefaultlibs.
Replace std:atomic with sanitizer atomics.

compiler-rt/trunk/lib/ubsan_minimal/CMakeLists.txt

 # Build for the undefined behavior sanitizer runtime support library.
 
 set(UBSAN_MINIMAL_SOURCES
   ubsan_minimal_handlers.cc
   )
 
 include_directories(..)
 
 set(UBSAN_CFLAGS ${SANITIZER_COMMON_CFLAGS})
 append_rtti_flag(OFF UBSAN_CFLAGS)
 
-set(UBSAN_STANDALONE_CFLAGS ${SANITIZER_COMMON_CFLAGS})
-append_rtti_flag(OFF UBSAN_STANDALONE_CFLAGS)
+set(UBSAN_LINK_FLAGS ${SANITIZER_COMMON_LINK_FLAGS})
+
+set(UBSAN_DYNAMIC_LIBS ${SANITIZER_COMMON_LINK_LIBS})
 
 add_compiler_rt_component(ubsan-minimal)
 
 # Common parts of UBSan runtime.
 add_compiler_rt_object_libraries(RTUbsan_minimal
   OS ${SANITIZER_COMMON_SUPPORTED_OS}
   ARCHS ${UBSAN_COMMON_SUPPORTED_ARCH}
   SOURCES ${UBSAN_MINIMAL_SOURCES} CFLAGS ${UBSAN_CFLAGS})
add_compiler_rt_runtime(clang_rt.ubsan_minimal
     PARENT_TARGET ubsan-minimal)
 
   add_compiler_rt_runtime(clang_rt.ubsan_minimal
     SHARED
     OS ${SANITIZER_COMMON_SUPPORTED_OS}
     ARCHS ${UBSAN_SUPPORTED_ARCH}
     OBJECT_LIBS RTUbsan_minimal
     CFLAGS ${UBSAN_CFLAGS}
+    LINK_FLAGS ${UBSAN_LINK_FLAGS}
     LINK_LIBS ${UBSAN_DYNAMIC_LIBS}
     PARENT_TARGET ubsan-minimal)
 
   if (UNIX AND NOT APPLE)
     set(ARCHS_FOR_SYMBOLS ${UBSAN_SUPPORTED_ARCH})
     list(REMOVE_ITEM ARCHS_FOR_SYMBOLS i386 i686)
     add_sanitizer_rt_symbols(clang_rt.ubsan_minimal
       ARCHS ${ARCHS_FOR_SYMBOLS}
       PARENT_TARGET ubsan-minimal
       EXTRA ubsan.syms.extra)
   endif()
 endif()

compiler-rt/trunk/lib/ubsan_minimal/ubsan_minimal_handlers.cc

-#include <atomic>
+#include "sanitizer_common/sanitizer_atomic.h"
+
 #include <stdlib.h>
+#include <stdint.h>
 #include <string.h>
 #include <unistd.h>
 
 static void message(const char *msg) {
   write(2, msg, strlen(msg));
 }
 
 static const int kMaxCallerPcs = 20;
-static std::atomic<void *> caller_pcs[kMaxCallerPcs];
+static __sanitizer::atomic_uintptr_t caller_pcs[kMaxCallerPcs];
 // Number of elements in caller_pcs. A special value of kMaxCallerPcs + 1 means
 // that "too many errors" has already been reported.
-static std::atomic<int> caller_pcs_sz;
+static __sanitizer::atomic_uint32_t caller_pcs_sz;
 
-__attribute__((noinline))
-static bool report_this_error(void *caller) {
-  if (caller == nullptr) return false;
+__attribute__((noinline)) static bool report_this_error(void *caller_p) {
+  uintptr_t caller = reinterpret_cast<uintptr_t>(caller_p);
+  if (caller == 0) return false;
   while (true) {
-    int sz = caller_pcs_sz.load(std::memory_order_relaxed);
-    if (sz > kMaxCallerPcs) return false; // early exit
+    unsigned sz = __sanitizer::atomic_load_relaxed(&caller_pcs_sz);
+    if (sz > kMaxCallerPcs) return false;  // early exit
     // when sz==kMaxCallerPcs print "too many errors", but only when cmpxchg
     // succeeds in order to not print it multiple times.
     if (sz > 0 && sz < kMaxCallerPcs) {
-      void *p;
-      for (int i = 0; i < sz; ++i) {
-        p = caller_pcs[i].load(std::memory_order_relaxed);
-        if (p == nullptr) break; // Concurrent update.
+      uintptr_t p;
+      for (unsigned i = 0; i < sz; ++i) {
+        p = __sanitizer::atomic_load_relaxed(&caller_pcs[i]);
+        if (p == 0) break;  // Concurrent update.
         if (p == caller) return false;
       }
-      if (p == nullptr) continue; // FIXME: yield?
+      if (p == 0) continue;  // FIXME: yield?
     }
 
-    if (!caller_pcs_sz.compare_exchange_strong(sz, sz + 1))
-      continue; // Concurrent update! Try again from the start.
+    if (!__sanitizer::atomic_compare_exchange_strong(
+            &caller_pcs_sz, &sz, sz + 1, __sanitizer::memory_order_seq_cst))
+      continue;  // Concurrent update! Try again from the start.
 
     if (sz == kMaxCallerPcs) {
       message("ubsan: too many errors\n");
       return false;
     }
-    caller_pcs[sz].store(caller, std::memory_order_relaxed);
+    __sanitizer::atomic_store_relaxed(&caller_pcs[sz], caller);
     return true;
   }
 }
 
 #if defined(__ANDROID__)
 extern "C" __attribute__((weak)) void android_set_abort_message(const char *);
 static void abort_with_message(const char *msg) {
   if (&android_set_abort_message) android_set_abort_message(msg);