build/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.

function usage_exit {
  echo "Usage: $0 [-f] [-r] [-n] <paths-to-binaries>..."
  echo "  -f forces replacement of an existing index."
  echo "  -r removes the index section."
  echo "  -n don't extract the dependencies of each binary with lld."
  echo "       e.g., $0 -n out/Debug/lib.unstripped/lib*"
  echo
  echo "  Set TOOLCHAIN_PREFIX to use a non-default set of binutils."
  exit 1
}

# 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 "$file")
  local should_index_this_file="${should_index}"

  local readelf_out=$(${TOOLCHAIN_PREFIX}readelf -S "$file")
  if [[ $readelf_out =~ "gdb_index" ]]; then
    if $remove_index; then
      ${TOOLCHAIN_PREFIX}objcopy --remove-section .gdb_index "$file"
      echo "Removed index from $basename."
    else
      echo "Skipped $basename -- already contains index."
      should_index_this_file=false
    fi
  fi

  if $should_index_this_file; then
    local start=$(date +"%s%N")
    echo "Adding index to $basename..."

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

remove_index=false
should_index=true
should_index_deps=true
files_to_index=()
while (($# > 0)); do
  case "$1" in
    -h)
      usage_exit
      ;;
    -f)
      remove_index=true
      ;;
    -r)
      remove_index=true
      should_index=false
      ;;
    -n)
      should_index_deps=false
      ;;
    -*)
      echo "Invalid option: $1" >&2
      usage_exit
      ;;
    *)
      if [[ ! -f "$1" ]]; then
        echo "Path $1 does not exist."
        exit 1
      fi
      files_to_index+=("$1")
      ;;
  esac
  shift
done

if ((${#files_to_index[@]} == 0)); then
  usage_exit
fi

dependencies=()
if $should_index_deps; then
  for file in "${files_to_index[@]}"; do
      # Append the shared library dependencies of this file that
      # have the same dirname. The dirname is a signal that these
      # shared libraries were part of the same build as the binary.
      dependencies+=( \
        $(ldd "$file" 2>/dev/null \
          | grep $(dirname "$file") \
          | sed "s/.*[ \t]\(.*\) (.*/\1/") \
      )
  done
fi
files_to_index+=("${dependencies[@]}")

# Ensure we cleanup on on exit.
trap on_exit EXIT INT

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

# 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