gdb-add-index

#!/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.
#
# Saves the gdb index for a given binary and its shared library dependencies.
#
# This will run gdb index in parallel on a number of binaries using SIGUSR1
# as the communication mechanism to simulate a semaphore. Because of the
# nature of this technique, using "set -e" is very difficult. The SIGUSR1
# terminates a "wait" with an error which we need to interpret.
#
# When modifying this code, most of the real logic is in the index_one_file
# function. The rest is cleanup + sempahore plumbing.

# Cleanup temp directory and ensure all child jobs are dead-dead.
function on_exit {
  trap "" EXIT USR1  # Avoid reentrancy.

  local jobs=$(jobs -p)
  if [ -n "$jobs" ]; then
    echo -n "Killing outstanding index jobs..."
    kill -KILL $(jobs -p)
    wait
    echo "done"
  fi

  if [ -f "$DIRECTORY" ]; then
    echo -n "Removing temp directory $DIRECTORY..."
    rm -rf $DIRECTORY
    echo done
  fi
}

# Add index to one binary.
function index_one_file {
  local file=$1
  local basename=$(basename "$file")

  local readelf_out=$(readelf -S "$file")
  if [[ $readelf_out =~ "gdb_index" ]]; then
    echo "Skipped $basename -- already contains index."
  else
    local start=$(date +"%s%N")
    echo "Adding index to $basename..."

    gdb -batch "$file" -ex "save gdb-index $DIRECTORY" -ex "quit"
    local index_file="$DIRECTORY/$basename.gdb-index"
    if [ -f "$index_file" ]; then
      objcopy --add-section .gdb_index="$index_file" \
        --set-section-flags .gdb_index=readonly "$file" "$file"
      local finish=$(date +"%s%N")
      local elappsed=$(((finish - start)/1000000))
      echo "   ...$basename indexed. [${elappsed}ms]"
    else
      echo "   ...$basename unindexable."
    fi
  fi
}

# Functions that when combined, concurrently index all files in FILES_TO_INDEX
# array. The global FILES_TO_INDEX is declared in the main body of the script.
function async_index {
  # Start a background subshell to run the index command.
  {
    index_one_file $1
    kill -SIGUSR1 $$  # $$ resolves to the parent script.
    exit 129  # See comment above wait loop at bottom.
  } &
}

CUR_FILE_NUM=0
function index_next {
  if (( CUR_FILE_NUM >= ${#FILES_TO_INDEX[@]} )); then
    return
  fi

  async_index "${FILES_TO_INDEX[CUR_FILE_NUM]}"
  ((CUR_FILE_NUM += 1)) || true
}


########
### Main body of the script.

if [[ ! $# == 1 ]]; then
  echo "Usage: $0 path-to-binary"
  exit 1
fi

FILENAME="$1"
if [[ ! -f "$FILENAME" ]]; then
  echo "Path $FILENAME does not exist."
  exit 1
fi

# Ensure we cleanup on on exit.
trap on_exit EXIT

# We're good to go! Create temp directory for index files.
DIRECTORY=$(mktemp -d)
echo "Made temp directory $DIRECTORY."

# Create array with the filename and all shared libraries that
# have the same dirname. The dirname is a signal that these
# shared libraries were part of the same build as the binary.
declare -a FILES_TO_INDEX=($FILENAME
 $(ldd "$FILENAME" 2>/dev/null \
  | grep $(dirname "$FILENAME") \
  | sed "s/.*[ \t]\(.*\) (.*/\1/")
)

# Start concurrent indexing.
trap index_next USR1

# 4 is an arbitrary default. When changing, remember we are likely IO bound
# so basing this off the number of cores is not sensible.
INDEX_TASKS=${INDEX_TASKS:-4}
for ((i=0;i<${INDEX_TASKS};i++)); do
  index_next
done

# Do a wait loop. Bash waits that terminate due a trap have an exit
# code > 128. We also ensure that our subshell's "normal" exit occurs with
# an exit code > 128. This allows us to do consider a > 128 exit code as
# an indication that the loop should continue. Unfortunately, it also means
# we cannot use set -e since technically the "wait" is failing.
wait
while (( $? > 128 )); do
  wait
done