dump_syms: add a -v flag

src/tools/linux/dump_syms/dump_syms.cc

 // Copyright (c) 2011, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 // copyright notice, this list of conditions and the following disclaimer
 // in the documentation and/or other materials provided with the
 // distribution.
 //     * Neither the name of Google Inc. nor the names of its
 // contributors may be used to endorse or promote products derived from
 // this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+#include <paths.h>
 #include <stdio.h>
+#include <unistd.h>
 
 #include <cstring>
 #include <iostream>
 #include <string>
 #include <vector>
 
 #include "common/linux/dump_symbols.h"
 
 using google_breakpad::WriteSymbolFile;
 
 int usage(const char* self) {
   fprintf(stderr, "Usage: %s [OPTION] <binary-with-debugging-info> "
           "[directories-for-debug-file]\n\n", self);
   fprintf(stderr, "Options:\n");
   fprintf(stderr, "  -c    Do not generate CFI section\n");
   fprintf(stderr, "  -r    Do not handle inter-compilation unit references\n");
+  fprintf(stderr, "  -v    Print all warnings to stderr\n");
   return 1;
 }
 
 int main(int argc, char **argv) {
   if (argc < 2)
     return usage(argv[0]);
 
   bool cfi = true;
   bool handle_inter_cu_refs = true;
+  bool log_to_stderr = false;
   int arg_index = 1;
   while (arg_index < argc && strlen(argv[arg_index]) > 0 &&
          argv[arg_index][0] == '-') {
     if (strcmp("-c", argv[arg_index]) == 0) {
       cfi = false;
     } else if (strcmp("-r", argv[arg_index]) == 0) {
       handle_inter_cu_refs = false;
+    } else if (strcmp("-v", argv[arg_index]) == 0) {
+      log_to_stderr = true;
     } else {
       return usage(argv[0]);
     }
     ++arg_index;
   }
   if (arg_index == argc)
     return usage(argv[0]);
 
+  // Save stderr so it can be used below.
+  FILE* saved_stderr = fdopen(dup(fileno(stderr)), "w");
+  if (!log_to_stderr) {
+    if (freopen(_PATH_DEVNULL, "w", stderr)) {
+      // If it fails, not a lot we can (or should) do.
+      // Add this brace section to silence gcc warnings.
+    }
+  }
+
   const char* binary;
   std::vector<string> debug_dirs;
   binary = argv[arg_index];
   for (int debug_dir_index = arg_index + 1;
        debug_dir_index < argc;
        ++debug_dir_index) {
     debug_dirs.push_back(argv[debug_dir_index]);
   }
 
   SymbolData symbol_data = cfi ? ALL_SYMBOL_DATA : NO_CFI;
   google_breakpad::DumpOptions options(symbol_data, handle_inter_cu_refs);
   if (!WriteSymbolFile(binary, debug_dirs, options, std::cout)) {
-    fprintf(stderr, "Failed to write symbol file.\n");
+    fprintf(saved_stderr, "Failed to write symbol file.\n");
     return 1;
   }
 
   return 0;
 }