We currently need this patch because ASan only searches PATH to find the
llvm-symbolizer binary to symbolize ASan traces. On testing machines, this
can be installed in PATH easily. However, for e.g. the ASan Nightly Project,
where we ship an ASan build, including llvm-symbolizer, to the user, we
cannot expect llvm-symbolizer to be on PATH. Instead, we should try to look
it up next to the binary. This patch implements the functionality for Linux
only until there is similar functionality provided upstream.

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_file.cc b/compiler-rt/lib/sanitizer_common/sanitizer_file.cc
index cde54bf..8daade1 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_file.cc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_file.cc
@@ -21,6 +21,10 @@
 #include "sanitizer_common.h"
 #include "sanitizer_file.h"
 
+#if SANITIZER_LINUX
+#include "sanitizer_posix.h"
+#endif
+
 namespace __sanitizer {
 
 void CatastrophicErrorWrite(const char *buffer, uptr length) {
@@ -156,6 +160,34 @@ char *FindPathToBinary(const char *name) {
     if (*end == '\0') break;
     beg = end + 1;
   }
+
+#if SANITIZER_LINUX
+  // If we cannot find the requested binary in PATH, we should try to locate
+  // it next to the binary, in case it is shipped with the build itself
+  // (e.g. llvm-symbolizer shipped with sanitizer build to symbolize on client.
+  if (internal_readlink("/proc/self/exe", buffer.data(), kMaxPathLength) < 0)
+    return nullptr;
+
+  uptr buf_len = internal_strlen(buffer.data());
+
+  /* Avoid using dirname() here */
+  while (buf_len > 0) {
+    if (buffer[buf_len - 1] == '/')
+      break;
+    buf_len--;
+  }
+
+  if (!buf_len)
+    return nullptr;
+
+  if (buf_len + name_len + 1 <= kMaxPathLength) {
+    internal_memcpy(&buffer[buf_len], name, name_len);
+    buffer[buf_len + name_len] = '\0';
+    if (FileExists(buffer.data()))
+      return internal_strdup(buffer.data());
+  }
+#endif
+
   return nullptr;
 }