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diff --git a/libsanitizer/sanitizer_common/sanitizer_coverage.cc b/libsanitizer/sanitizer_common/sanitizer_coverage.cc
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+++ b/libsanitizer/sanitizer_common/sanitizer_coverage.cc
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+//===-- sanitizer_coverage.cc ---------------------------------------------===//
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Sanitizer Coverage.
+// This file implements run-time support for a poor man's coverage tool.
+//
+// Compiler instrumentation:
+// For every function F the compiler injects the following code:
+// if (*Guard) {
+//    __sanitizer_cov(&F);
+//    *Guard = 1;
+// }
+// It's fine to call __sanitizer_cov more than once for a given function.
+//
+// Run-time:
+//  - __sanitizer_cov(pc): record that we've executed a given PC.
+//  - __sanitizer_cov_dump: dump the coverage data to disk.
+//  For every module of the current process that has coverage data
+//  this will create a file module_name.PID.sancov. The file format is simple:
+//  it's just a sorted sequence of 4-byte offsets in the module.
+//
+// Eventually, this coverage implementation should be obsoleted by a more
+// powerful general purpose Clang/LLVM coverage instrumentation.
+// Consider this implementation as prototype.
+//
+// FIXME: support (or at least test with) dlclose.
+//===----------------------------------------------------------------------===//
+
+#include "sanitizer_allocator_internal.h"
+#include "sanitizer_common.h"
+#include "sanitizer_libc.h"
+#include "sanitizer_mutex.h"
+#include "sanitizer_procmaps.h"
+#include "sanitizer_flags.h"
+
+struct CovData {
+  BlockingMutex mu;
+  InternalMmapVector<uptr> v;
+};
+
+static uptr cov_data_placeholder[sizeof(CovData) / sizeof(uptr)];
+COMPILER_CHECK(sizeof(cov_data_placeholder) >= sizeof(CovData));
+static CovData *cov_data = reinterpret_cast<CovData*>(cov_data_placeholder);
+
+namespace __sanitizer {
+
+// Simply add the pc into the vector under lock. If the function is called more
+// than once for a given PC it will be inserted multiple times, which is fine.
+static void CovAdd(uptr pc) {
+  BlockingMutexLock lock(&cov_data->mu);
+  cov_data->v.push_back(pc);
+}
+
+static inline bool CompareLess(const uptr &a, const uptr &b) {
+  return a < b;
+}
+
+// Dump the coverage on disk.
+void CovDump() {
+#if !SANITIZER_WINDOWS
+  BlockingMutexLock lock(&cov_data->mu);
+  InternalMmapVector<uptr> &v = cov_data->v;
+  InternalSort(&v, v.size(), CompareLess);
+  InternalMmapVector<u32> offsets(v.size());
+  const uptr *vb = v.data();
+  const uptr *ve = vb + v.size();
+  MemoryMappingLayout proc_maps(/*cache_enabled*/false);
+  uptr mb, me, off, prot;
+  InternalScopedBuffer<char> module(4096);
+  InternalScopedBuffer<char> path(4096 * 2);
+  for (int i = 0;
+       proc_maps.Next(&mb, &me, &off, module.data(), module.size(), &prot);
+       i++) {
+    if ((prot & MemoryMappingLayout::kProtectionExecute) == 0)
+      continue;
+    if (vb >= ve) break;
+    if (mb <= *vb && *vb < me) {
+      offsets.clear();
+      const uptr *old_vb = vb;
+      CHECK_LE(off, *vb);
+      for (; vb < ve && *vb < me; vb++) {
+        uptr diff = *vb - (i ? mb : 0) + off;
+        CHECK_LE(diff, 0xffffffffU);
+        offsets.push_back(static_cast<u32>(diff));
+      }
+      char *module_name = StripModuleName(module.data());
+      internal_snprintf((char *)path.data(), path.size(), "%s.%zd.sancov",
+                        module_name, internal_getpid());
+      InternalFree(module_name);
+      uptr fd = OpenFile(path.data(), true);
+      internal_write(fd, offsets.data(), offsets.size() * sizeof(u32));
+      internal_close(fd);
+      if (common_flags()->verbosity)
+        Report(" CovDump: %s: %zd PCs written\n", path.data(), vb - old_vb);
+    }
+  }
+#endif  // !SANITIZER_WINDOWS
+}
+
+}  // namespace __sanitizer
+
+extern "C" {
+SANITIZER_INTERFACE_ATTRIBUTE void __sanitizer_cov(void *pc) {
+  CovAdd(reinterpret_cast<uptr>(pc));
+}
+SANITIZER_INTERFACE_ATTRIBUTE void __sanitizer_cov_dump() { CovDump(); }
+}  // extern "C"