blob: d6b715dbae3babe3b1e9a88077a11c79a3461cf9 [file] [log] [blame]
#!/usr/bin/env python
"""wrapper around emcc link step.
This wrapper currently serves the following purposes.
1. When building with --config=wasm the final output is multiple files, usually
at least one .js and one .wasm file. Since the cc_binary link step only
allows a single output, we must tar up the outputs into a single file.
2. Add quotes around arguments that need them in the response file to work
around a bazel quirk.
3. Ensure the external_debug_info section of the wasm points at the correct
bazel path.
from __future__ import print_function
import argparse
import os
import subprocess
import sys
# Only argument should be @path/to/parameter/file
assert sys.argv[1][0] == '@', sys.argv
param_filename = sys.argv[1][1:]
param_file_args = [l.strip() for l in open(param_filename, 'r').readlines()]
# Re-write response file if needed.
if any(' ' in a for a in param_file_args):
new_param_filename = param_filename + '.modified'
with open(new_param_filename, 'w') as f:
for param in param_file_args:
if ' ' in param:
f.write('"%s"' % param)
sys.argv[1] = '@' + new_param_filename
emcc_py = os.path.join(os.environ['EMSCRIPTEN'], '')
rtn =[sys.executable, emcc_py] + sys.argv[1:])
if rtn != 0:
# Parse the arguments that we gave to the linker to determine what the output
# file is named and what the output format is.
parser = argparse.ArgumentParser(add_help=False)
options = parser.parse_known_args(param_file_args)[0]
output_file = options.o
oformat = options.oformat
outdir = os.path.normpath(os.path.dirname(output_file))
base_name = os.path.basename(output_file)
# The output file name is the name of the build rule that was built.
# Add an appropriate file extension based on --oformat.
if oformat is not None:
base_name_split = os.path.splitext(base_name)
# If the output name has no extension, give it the appropriate extension.
if not base_name_split[1]:
os.rename(output_file, output_file + '.' + oformat)
# If the output name does have an extension and it matches the output format,
# change the base_name so it doesn't have an extension.
elif base_name_split[1] == '.' + oformat:
base_name = base_name_split[0]
# If the output name does have an extension and it does not match the output
# format, change the base_name so it doesn't have an extension and rename
# the output_file so it has the proper extension.
# Note that if you do something like name your build rule "foo.js" and pass
# "--oformat=html", emscripten will write to the same file for both the js and
# html output, overwriting the js output entirely with the html.
# Please don't do that.
base_name = base_name_split[0]
os.rename(output_file, os.path.join(outdir, base_name + '.' + oformat))
files = []
extensions = [
for ext in extensions:
filename = base_name + ext
if os.path.exists(os.path.join(outdir, filename)):
wasm_base = os.path.join(outdir, base_name + '.wasm')
if os.path.exists(wasm_base + '.debug.wasm') and os.path.exists(wasm_base):
# If we have a .wasm.debug.wasm file and a .wasm file, we need to rewrite the
# section in the .wasm file that refers to it. The path that's in there
# is the blaze output path; we want it to be just the filename.
llvm_objcopy = os.path.join(
os.environ['EM_BIN_PATH'], 'bin/llvm-objcopy')
# First, check to make sure the .wasm file has the header that needs to be
# rewritten.
rtn =[
wasm_base], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
if rtn == 0:
# If llvm-objcopy did not return an error, the external_debug_info section
# must exist, so we're good to continue.
# Next we need to convert length of the filename to LEB128.
# Start by converting the length of the filename to a bit string.
bit_string = '{0:b}'.format(len(base_name + '.wasm.debug.wasm'))
# Pad the bit string with 0s so that its length is a multiple of 7.
while len(bit_string) % 7 != 0:
bit_string = '0' + bit_string
# Break up our bit string into chunks of 7.
# We do this backwards because the final format is little-endian.
final_bytes = bytearray()
for i in reversed(range(0, len(bit_string), 7)):
binary_part = bit_string[i:i + 7]
if i != 0:
# Every chunk except the last one needs to be prepended with '1'.
# The length of each chunk is 7, so that one has an implicit '0'.
binary_part = '1' + binary_part
final_bytes.append(int(binary_part, 2))
# Finally, add the actual filename.
final_bytes.extend((base_name + '.wasm.debug.wasm').encode())
# Write our length + filename bytes to a temp file.
with open('debugsection.tmp', 'wb+') as f:
# First delete the old section.
# Rewrite section with the new size and filename from the temp file.
# Make sure we have at least one output file.
if not len(files):
print(' did not appear to output any known files!')
# cc_binary must output exactly one file; put all the output files in a tarball.
cmd = ['tar', 'cf', 'tmp.tar'] + files
subprocess.check_call(cmd, cwd=outdir)
os.rename(os.path.join(outdir, 'tmp.tar'), output_file)