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#!/usr/bin/env python3
# Copyright 2021 The Pigweed Authors
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may not
# use this file except in compliance with the License. You may obtain a copy of
# the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations under
# the License.
"""Generates flags needed for an ARM build using clang.
Using clang on Cortex-M cores isn't intuitive as the end-to-end experience isn't
quite completely in LLVM. LLVM doesn't yet provide compatible C runtime
libraries or C/C++ standard libraries. To work around this, this script pulls
the missing bits from an arm-none-eabi-gcc compiler on the system path. This
lets clang do the heavy lifting while only relying on some headers provided by
newlib/arm-none-eabi-gcc in addition to a small assortment of needed libraries.
To use this script, specify what flags you want from the script, and run with
the required architecture flags like you would with gcc:
python -m pw_toolchain.clang_arm_toolchain --cflags -- -mthumb -mcpu=cortex-m3
The script will then print out the additional flags you need to pass to clang to
get a working build.
"""
import argparse
import sys
import os
import subprocess
from pathlib import Path
from typing import List, Dict, Tuple
_ARM_COMPILER_PREFIX = 'arm-none-eabi'
_ARM_COMPILER_NAME = _ARM_COMPILER_PREFIX + '-gcc'
def _parse_args() -> argparse.Namespace:
"""Parses arguments for this script, splitting out the command to run."""
parser = argparse.ArgumentParser(description=__doc__)
parser.add_argument(
'--gn-scope',
action='store_true',
help=(
"Formats the output like a GN scope so it can be ingested by "
"exec_script()"
),
)
parser.add_argument(
'--cflags',
action='store_true',
help=('Include necessary C flags in the output'),
)
parser.add_argument(
'--ldflags',
action='store_true',
help=('Include necessary linker flags in the output'),
)
parser.add_argument(
'clang_flags',
nargs=argparse.REMAINDER,
help='Flags to pass to clang, which can affect library/include paths',
)
parsed_args = parser.parse_args()
assert parsed_args.clang_flags[0] == '--', 'arguments not correctly split'
parsed_args.clang_flags = parsed_args.clang_flags[1:]
return parsed_args
def _compiler_info_command(print_command: str, cflags: List[str]) -> str:
command = [_ARM_COMPILER_NAME]
command.extend(cflags)
command.append(print_command)
result = subprocess.run(
command,
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT,
)
result.check_returncode()
return result.stdout.decode().rstrip()
def get_gcc_lib_dir(cflags: List[str]) -> Path:
return Path(
_compiler_info_command('-print-libgcc-file-name', cflags)
).parent
def get_compiler_info(cflags: List[str]) -> Dict[str, str]:
compiler_info: Dict[str, str] = {}
compiler_info['gcc_libs_dir'] = os.path.relpath(
str(get_gcc_lib_dir(cflags)), "."
)
compiler_info['sysroot'] = os.path.relpath(
_compiler_info_command('-print-sysroot', cflags), "."
)
compiler_info['version'] = _compiler_info_command('-dumpversion', cflags)
compiler_info['multi_dir'] = _compiler_info_command(
'-print-multi-directory', cflags
)
return compiler_info
def get_cflags(compiler_info: Dict[str, str]):
"""TODO(amontanez): Add docstring."""
# TODO(amontanez): Make newlib-nano optional.
cflags = [
# TODO(amontanez): For some reason, -stdlib++-isystem and
# -isystem-after work, but emit unused argument errors. This is the only
# way to let the build succeed.
'-Qunused-arguments',
# Disable all default libraries.
"-nodefaultlibs",
'--target=arm-none-eabi',
]
# Add sysroot info.
cflags.extend(
(
'--sysroot=' + compiler_info['sysroot'],
'-isystem'
+ str(Path(compiler_info['sysroot']) / 'include' / 'newlib-nano'),
# This must be included after Clang's builtin headers.
'-isystem-after' + str(Path(compiler_info['sysroot']) / 'include'),
'-stdlib++-isystem'
+ str(
Path(compiler_info['sysroot'])
/ 'include'
/ 'c++'
/ compiler_info['version']
),
'-isystem'
+ str(
Path(compiler_info['sysroot'])
/ 'include'
/ 'c++'
/ compiler_info['version']
/ _ARM_COMPILER_PREFIX
/ compiler_info['multi_dir']
),
)
)
return cflags
def get_crt_objs(compiler_info: Dict[str, str]) -> Tuple[str, ...]:
return (
str(Path(compiler_info['gcc_libs_dir']) / 'crtfastmath.o'),
str(Path(compiler_info['gcc_libs_dir']) / 'crti.o'),
str(Path(compiler_info['gcc_libs_dir']) / 'crtn.o'),
str(
Path(compiler_info['sysroot'])
/ 'lib'
/ compiler_info['multi_dir']
/ 'crt0.o'
),
)
def get_ldflags(compiler_info: Dict[str, str]) -> List[str]:
ldflags: List[str] = [
# Add library search paths.
'-L' + compiler_info['gcc_libs_dir'],
'-L'
+ str(
Path(compiler_info['sysroot']) / 'lib' / compiler_info['multi_dir']
),
# Add libraries to link.
'-lc_nano',
'-lm',
'-lgcc',
'-lstdc++_nano',
]
# Add C runtime object files.
objs = get_crt_objs(compiler_info)
ldflags.extend(objs)
return ldflags
def main(
cflags: bool,
ldflags: bool,
gn_scope: bool,
clang_flags: List[str],
) -> int:
"""Script entry point."""
compiler_info = get_compiler_info(clang_flags)
if ldflags:
ldflag_list = get_ldflags(compiler_info)
if cflags:
cflag_list = get_cflags(compiler_info)
if not gn_scope:
flags = []
if cflags:
flags.extend(cflag_list)
if ldflags:
flags.extend(ldflag_list)
print(' '.join(flags))
return 0
if cflags:
print('cflags = [')
for flag in cflag_list:
print(f' "{flag}",')
print(']')
if ldflags:
print('ldflags = [')
for flag in ldflag_list:
print(f' "{flag}",')
print(']')
return 0
if __name__ == '__main__':
sys.exit(main(**vars(_parse_args())))
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