Have valgrind use a gdb that matches the word width of the binary.

tools/valgrind/valgrind.sh

 #!/bin/bash
 
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This is a small script for manually launching valgrind, along with passing
 # it the suppression file, and some helpful arguments (automatically attaching
 # the debugger on failures, etc).  Run it from your repo root, something like:
 #  $ sh ./tools/valgrind/valgrind.sh ./out/Debug/chrome
 #
 # This is mostly intended for running the chrome browser interactively.
 # To run unit tests, you probably want to run chrome_tests.sh instead.
 # That's the script used by the valgrind buildbot.
 
 export THISDIR=`dirname $0`
 
 setup_memcheck() {
   RUN_COMMAND="valgrind"
-  # Prefer a 32-bit gdb if it's available.
-  GDB="/usr/bin/gdb32";
-  if [ ! -x $GDB ]; then
-    GDB="gdb"
+  GDB=gdb
+  EXE_INFO=$(file $1)
+  if [[ $? -eq 0 ]]; then
+    # Prefer a gdb that matches the executable if it's available.
+    if [[ "$EXE_INFO" == *32-bit* && -x /usr/bin/gdb32 ]]; then
+      GDB="/usr/bin/gdb32";
+    elif [[ "$EXE_INFO" == *64-bit* && -x /usr/bin/gdb64 ]]; then
+      GDB="/usr/bin/gdb64";
+    fi
   fi
 
   # Prompt to attach gdb when there was an error detected.
   DEFAULT_TOOL_FLAGS=("--db-command=$GDB -nw %f %p" "--db-attach=yes" \
                       # Keep the registers in gdb in sync with the code.
                       "--vex-iropt-precise-memory-exns=yes" \
                       # Overwrite newly allocated or freed objects
                       # with 0x41 to catch inproper use.
                       "--malloc-fill=41" "--free-fill=41" \
                       # Increase the size of stacks being tracked.
@@ skipping 28 matching lines @@
   TOOL_NAME="$TMP_STR"
   shift
 fi
 
 if echo "$@" | grep "\-\-tool" ; then
   echo "--tool=TOOL must be the first argument" >&2
   exit 1
 fi
 
 case $TOOL_NAME in
-  memcheck*)  setup_memcheck;;
+  memcheck*)  setup_memcheck "$1";;
   tsan*)      setup_tsan;;
   *)          setup_unknown;;
 esac
 
 
 SUPPRESSIONS="$THISDIR/$TOOL_NAME/suppressions.txt"
 
 CHROME_VALGRIND=`sh $THISDIR/locate_valgrind.sh`
 if [ "$CHROME_VALGRIND" = "" ]
 then
@@ skipping 26 matching lines @@
 G_SLICE=always-malloc \
 NSS_DISABLE_UNLOAD=1 \
 NSS_DISABLE_ARENA_FREE_LIST=1 \
 G_DEBUG=fatal_warnings \
 GTEST_DEATH_TEST_USE_FORK=1 \
 $RUN_COMMAND \
   --trace-children=yes \
   --suppressions="$SUPPRESSIONS" \
   "${DEFAULT_TOOL_FLAGS[@]}" \
   "$@"