# Copyright (c) Meta Platforms, Inc. and affiliates.
#
# This source code is licensed under both the MIT license found in the
# LICENSE-MIT file in the root directory of this source tree and the Apache
# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
# of this source tree.
load(
"@prelude//cxx:cxx_toolchain_types.bzl",
"CxxToolchainInfo",
"LinkerType",
)
load("@prelude//cxx:debug.bzl", "SplitDebugMode")
# Styles of LTO.
LtoMode = enum(
# No LTO
"none",
# Object files contain both LTO IR and native code to allow binaries to link
# either via standard or LTO.
"fat",
# Traditional, monolithic LTO.
"monolithic",
# https://clang.llvm.org/docs/ThinLTO.html
"thin",
)
def lto_compiler_flags(lto_mode: LtoMode) -> list[str]:
if lto_mode == LtoMode("none"):
return []
elif lto_mode == LtoMode("fat") or lto_mode == LtoMode("monolithic"):
return ["-flto=full"]
elif lto_mode == LtoMode("thin"):
return ["-flto=thin"]
else:
fail("Unhandled LTO mode: " + repr(lto_mode))
SplitDebugLtoInfo = record(
# The output that the linker will generate split debug object(s) too. May
# be a single object file (e.g. for darwin+monoLTO) or a directory.
output = field(Artifact),
# The flags to add to the link to use the above output.
linker_flags = field(cmd_args),
)
def get_split_debug_lto_info(actions: AnalysisActions, cxx_toolchain: CxxToolchainInfo, name: str) -> [SplitDebugLtoInfo, None]:
linker_info = cxx_toolchain.linker_info
# We only generate these flags for LTO+DWO.
if cxx_toolchain.split_debug_mode == SplitDebugMode("none"):
return None
if cxx_toolchain.linker_info.lto_mode == LtoMode("none"):
return None
# TODO: It might be nice to generalize a but more and move the darwin v. gnu
# differences into toolchain settings (e.g. `split_debug_lto_flags_fmt`).
if linker_info.type == LinkerType("darwin"):
# https://releases.llvm.org/14.0.0/tools/clang/docs/CommandGuide/clang.html#cmdoption-flto
# We need to pass -object_path_lto to keep the temporary LTO object files around to use
# for dSYM generation.
if linker_info.lto_mode == LtoMode("thin"):
# For thin LTO the path is a folder that will contain the various object files.
lto_object_path_artifact = actions.declare_output("lto_object_files", dir = True)
else:
# For monolithic LTO the path is a single object file.
lto_object_path_artifact = actions.declare_output("lto_object_file.o", dir = False)
linker_args = cmd_args([
# Use -Xlinker in case the path has a ,
"-Xlinker",
"-object_path_lto",
"-Xlinker",
lto_object_path_artifact.as_output(),
])
return SplitDebugLtoInfo(
output = lto_object_path_artifact,
linker_flags = linker_args,
)
if linker_info.type == LinkerType("gnu"):
dwo_dir = actions.declare_output(name + ".dwo.d", dir = True)
linker_flags = cmd_args([
"-Xlinker",
"-plugin-opt",
"-Xlinker",
# NOTE: can't use -Wl,plugin-opt,dwo_dir=... because the $(output ...)
# macro might be expanded to a value with commas breaking -Wl, parsing.
cmd_args(dwo_dir.as_output(), format = "dwo_dir={}"),
])
return SplitDebugLtoInfo(
output = dwo_dir,
linker_flags = linker_flags,
)
fail("can't handle split-debug+LTO for linker type: {}".format(linker_info.type))