1 files changed, 27 insertions, 1 deletions

diff --git a/third_party/tcmalloc/vendor/src/symbolize.cc b/third_party/tcmalloc/vendor/src/symbolize.cc
index dfdfb7e..d90c4b8 100644
--- a/third_party/tcmalloc/vendor/src/symbolize.cc
+++ b/third_party/tcmalloc/vendor/src/symbolize.cc
@@ -57,6 +57,7 @@
 #endif
 #include <string>
 #include "base/commandlineflags.h"
+#include "base/logging.h"
 #include "base/sysinfo.h"
 
 using std::string;
@@ -93,6 +94,15 @@ static char* GetProgramInvocationName() {
 #endif
 }
 
+// Prints an error message when you can't run Symbolize().
+static void PrintError(const char* reason) {
+  RAW_LOG(ERROR,
+          "*** WARNING: Cannot convert addresses to symbols in output below.\n"
+          "*** Reason: %s\n"
+          "*** If you cannot fix this, try running pprof directly.\n",
+          reason);
+}
+
 void SymbolTable::Add(const void* addr) {
   symbolization_table_[addr] = "";
 }
@@ -107,13 +117,22 @@ const char* SymbolTable::GetSymbol(const void* addr) {
 // Note that the forking/etc is not thread-safe or re-entrant.  That's
 // ok for the purpose we need -- reporting leaks detected by heap-checker
 // -- but be careful if you decide to use this routine for other purposes.
+// Returns number of symbols read on error.  If can't symbolize, returns 0
+// and emits an error message about why.
 int SymbolTable::Symbolize() {
 #if !defined(HAVE_UNISTD_H)  || !defined(HAVE_SYS_SOCKET_H) || !defined(HAVE_SYS_WAIT_H)
+  PrintError("Perftools does not know how to call a sub-process on this O/S");
   return 0;
 #else
   const char* argv0 = GetProgramInvocationName();
-  if (argv0 == NULL)   // can't call symbolize if we can't figure out our name
+  if (argv0 == NULL) {  // can't call symbolize if we can't figure out our name
+    PrintError("Cannot figure out the name of this executable (argv0)");
     return 0;
+  }
+  if (access(g_pprof_path->c_str(), R_OK) != 0) {
+    PrintError("Cannot find 'pprof' (is PPROF_PATH set correctly?)");
+    return 0;
+  }
 
   // All this work is to do two-way communication.  ugh.
   int *child_in = NULL;   // file descriptors
@@ -131,6 +150,7 @@ int SymbolTable::Symbolize() {
       for (int j = 0; j < i; j++) {
         close(child_fds[j][0]);
         close(child_fds[j][1]);
+        PrintError("Cannot create a socket pair");
         return 0;
       }
     } else {
@@ -156,6 +176,7 @@ int SymbolTable::Symbolize() {
       close(child_in[1]);
       close(child_out[0]);
       close(child_out[1]);
+      PrintError("Unknown error calling fork()");
       return 0;
     }
     case 0: {  // child
@@ -178,6 +199,8 @@ int SymbolTable::Symbolize() {
       close(child_in[0]);   // child uses the 0's, parent uses the 1's
       close(child_out[0]);  // child uses the 0's, parent uses the 1's
 #ifdef HAVE_POLL_H
+      // Waiting for 1ms seems to give the OS time to notice any errors.
+      poll(0, 0, 1);
       // For maximum safety, we check to make sure the execlp
       // succeeded before trying to write.  (Otherwise we'll get a
       // SIGPIPE.)  For systems without poll.h, we'll just skip this
@@ -185,6 +208,7 @@ int SymbolTable::Symbolize() {
       struct pollfd pfd = { child_in[1], POLLOUT, 0 };
       if (!poll(&pfd, 1, 0) || !(pfd.revents & POLLOUT) ||
           (pfd.revents & (POLLHUP|POLLERR))) {
+        PrintError("Cannot run 'pprof' (is PPROF_PATH set correctly?)");
         return 0;
       }
 #endif
@@ -220,6 +244,7 @@ int SymbolTable::Symbolize() {
                               kSymbolBufferSize - total_bytes_read);
         if (bytes_read < 0) {
           close(child_out[1]);
+          PrintError("Cannot read data from pprof");
           return 0;
         } else if (bytes_read == 0) {
           close(child_out[1]);
@@ -249,6 +274,7 @@ int SymbolTable::Symbolize() {
       return num_symbols;
     }
   }
+  PrintError("Unkown error (should never occur!)");
   return 0;  // shouldn't be reachable
 #endif
 }