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skia2/toolchain/linux_amd64_toolchain_config.bzl
Kevin Lubick 590d3cc8f7 [bazel] Re-implement IWYU enforcement 
Instead of having a feature that a subpackage cc_library
would set (because the subpackage cc_libraries went away in
review.skia.org/543977), we now have a list of directories
for which all descendent files will have IWYU run on them.

As before, we have an overarching feature "skia_enforce_iwyu"
that enables this check because of the extra compilation
overhead it incurs.

We have decided to enforce IWYU on debug builds instead of
release builds because we have some code (e.g. that in
SkDEBUGCODE or SkASSERT) which is only compiled and executed
in a debug build, but we don't want to have
#if defined(SK_DEBUG)
all over the place. We make the assumption that the includes
needed to compile in debug mode are the superset of the
includes necessary for release and other modes.

Change-Id: I10254fcc162627c20eb89959e06417effa3cc396
Bug: skia:12541 skia:13052
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/546607
Reviewed-by: Ben Wagner <bungeman@google.com>
2022-06-06 14:29:47 +00:00

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"""
This file specifies a clang toolchain that can run on a Linux host which doesn't depend on any
installed packages from the host machine.
See download_linux_amd64_toolchain.bzl for more details on the creation of the toolchain.
It uses the usr subfolder of the built toolchain as a sysroot
It follows the example of:
- https://docs.bazel.build/versions/4.2.1/tutorial/cc-toolchain-config.html
- https://github.com/emscripten-core/emsdk/blob/7f39d100d8cd207094decea907121df72065517e/bazel/emscripten_toolchain/crosstool.bzl
"""
load(
"@bazel_tools//tools/cpp:cc_toolchain_config_lib.bzl",
"action_config",
"feature",
"flag_group",
"flag_set",
"tool",
"variable_with_value",
)
# https://github.com/bazelbuild/bazel/blob/master/tools/build_defs/cc/action_names.bzl
load("@bazel_tools//tools/build_defs/cc:action_names.bzl", "ACTION_NAMES")
# The location of the created clang toolchain.
EXTERNAL_TOOLCHAIN = "external/clang_linux_amd64"
def _linux_amd64_toolchain_info(ctx):
action_configs = _make_action_configs()
features = []
features += _make_default_flags()
features += _make_diagnostic_flags()
features += _make_iwyu_flags()
# https://docs.bazel.build/versions/main/skylark/lib/cc_common.html#create_cc_toolchain_config_info
# Note, this rule is defined in Java code, not Starlark
# https://cs.opensource.google/bazel/bazel/+/master:src/main/java/com/google/devtools/build/lib/starlarkbuildapi/cpp/CcModuleApi.java
return cc_common.create_cc_toolchain_config_info(
ctx = ctx,
features = features,
abi_libc_version = "unknown",
abi_version = "unknown",
action_configs = action_configs,
# This is important because the linker will complain if the libc shared libraries are not
# under this directory. Because we extract the libc libraries to
# EXTERNAL_TOOLCHAIN/lib, and the various headers and shared libraries to
# EXTERNAL_TOOLCHAIN/usr, we make the top level folder the sysroot so the linker can
# find the referenced libraries (e.g. EXTERNAL_TOOLCHAIN/usr/lib/x86_64-linux-gnu/libc.so
# is just a text file that refers to "/lib/x86_64-linux-gnu/libc.so.6" and
# "/lib64/ld-linux-x86-64.so.2" which will use the sysroot as the root).
builtin_sysroot = EXTERNAL_TOOLCHAIN,
compiler = "clang",
host_system_name = "local",
target_cpu = "k8",
# It is unclear if target_libc matters.
target_libc = "glibc-2.31",
target_system_name = "local",
toolchain_identifier = "clang-toolchain",
)
provide_linux_amd64_toolchain_config = rule(
attrs = {},
provides = [CcToolchainConfigInfo],
implementation = _linux_amd64_toolchain_info,
)
def _make_action_configs():
"""
This function sets up the tools needed to perform the various compile/link actions.
Bazel normally restricts us to referring to (and therefore running) executables/scripts
that are in this directory (That is EXEC_ROOT/toolchain). However, the executables we want
to run are brought in via WORKSPACE.bazel and are located in EXEC_ROOT/external/clang....
Therefore, we make use of "trampoline scripts" that will call the binaries from the
toolchain directory.
These action_configs also let us dynamically specify arguments from the Bazel
environment if necessary (see cpp_link_static_library_action).
"""
# https://cs.opensource.google/bazel/bazel/+/master:tools/cpp/cc_toolchain_config_lib.bzl;l=435;drc=3b9e6f201a9a3465720aad8712ab7bcdeaf2e5da
clang_tool = tool(path = "linux_trampolines/clang_trampoline_linux.sh")
lld_tool = tool(path = "linux_trampolines/lld_trampoline_linux.sh")
ar_tool = tool(path = "linux_trampolines/ar_trampoline_linux.sh")
# https://cs.opensource.google/bazel/bazel/+/master:tools/cpp/cc_toolchain_config_lib.bzl;l=488;drc=3b9e6f201a9a3465720aad8712ab7bcdeaf2e5da
assemble_action = action_config(
action_name = ACTION_NAMES.assemble,
tools = [clang_tool],
)
c_compile_action = action_config(
action_name = ACTION_NAMES.c_compile,
tools = [clang_tool],
)
cpp_compile_action = action_config(
action_name = ACTION_NAMES.cpp_compile,
tools = [clang_tool],
)
linkstamp_compile_action = action_config(
action_name = ACTION_NAMES.linkstamp_compile,
tools = [clang_tool],
)
preprocess_assemble_action = action_config(
action_name = ACTION_NAMES.preprocess_assemble,
tools = [clang_tool],
)
cpp_link_dynamic_library_action = action_config(
action_name = ACTION_NAMES.cpp_link_dynamic_library,
tools = [lld_tool],
)
cpp_link_executable_action = action_config(
action_name = ACTION_NAMES.cpp_link_executable,
# Bazel assumes it is talking to clang when building an executable. There are
# "-Wl" flags on the command: https://releases.llvm.org/6.0.1/tools/clang/docs/ClangCommandLineReference.html#cmdoption-clang-Wl
tools = [clang_tool],
)
cpp_link_nodeps_dynamic_library_action = action_config(
action_name = ACTION_NAMES.cpp_link_nodeps_dynamic_library,
tools = [lld_tool],
)
# This is the same rule as
# https://github.com/emscripten-core/emsdk/blob/7f39d100d8cd207094decea907121df72065517e/bazel/emscripten_toolchain/crosstool.bzl#L143
# By default, there are no flags or libraries passed to the llvm-ar tool, so
# we need to specify them. The variables mentioned by expand_if_available are defined
# https://docs.bazel.build/versions/main/cc-toolchain-config-reference.html#cctoolchainconfiginfo-build-variables
cpp_link_static_library_action = action_config(
action_name = ACTION_NAMES.cpp_link_static_library,
flag_sets = [
flag_set(
flag_groups = [
flag_group(
# https://llvm.org/docs/CommandGuide/llvm-ar.html
# replace existing files or insert them if they already exist,
# create the file if it doesn't already exist
# symbol table should be added
# Deterministic timestamps should be used
flags = ["rcsD", "%{output_execpath}"],
# Despite the name, output_execpath just refers to linker output,
# e.g. libFoo.a
expand_if_available = "output_execpath",
),
],
),
flag_set(
flag_groups = [
flag_group(
iterate_over = "libraries_to_link",
flag_groups = [
flag_group(
flags = ["%{libraries_to_link.name}"],
expand_if_equal = variable_with_value(
name = "libraries_to_link.type",
value = "object_file",
),
),
flag_group(
flags = ["%{libraries_to_link.object_files}"],
iterate_over = "libraries_to_link.object_files",
expand_if_equal = variable_with_value(
name = "libraries_to_link.type",
value = "object_file_group",
),
),
],
expand_if_available = "libraries_to_link",
),
],
),
flag_set(
flag_groups = [
flag_group(
flags = ["@%{linker_param_file}"],
expand_if_available = "linker_param_file",
),
],
),
],
tools = [ar_tool],
)
action_configs = [
assemble_action,
c_compile_action,
cpp_compile_action,
cpp_link_dynamic_library_action,
cpp_link_executable_action,
cpp_link_nodeps_dynamic_library_action,
cpp_link_static_library_action,
linkstamp_compile_action,
preprocess_assemble_action,
]
return action_configs
def _make_default_flags():
"""Here we define the flags for certain actions that are always applied."""
cxx_compile_includes = flag_set(
actions = [
ACTION_NAMES.c_compile,
ACTION_NAMES.cpp_compile,
],
flag_groups = [
flag_group(
flags = [
# THIS ORDER MATTERS GREATLY. If these are in the wrong order, the
# #include_next directives will fail to find the files, causing a compilation
# error (or, without -no-canonical-prefixes, a mysterious case where files
# are included with an absolute path and fail the build).
"-isystem",
EXTERNAL_TOOLCHAIN + "/include/c++/v1",
"-isystem",
EXTERNAL_TOOLCHAIN + "/usr/include",
"-isystem",
EXTERNAL_TOOLCHAIN + "/lib/clang/13.0.0/include",
"-isystem",
EXTERNAL_TOOLCHAIN + "/usr/include/x86_64-linux-gnu",
# We do not want clang to search in absolute paths for files. This makes
# Bazel think we are using an outside resource and fail the compile.
"-no-canonical-prefixes",
],
),
],
)
cpp_compile_includes = flag_set(
actions = [
ACTION_NAMES.cpp_compile,
],
flag_groups = [
flag_group(
flags = [
"-std=c++17",
"-Wno-psabi", # noisy
],
),
],
)
link_exe_flags = flag_set(
actions = [ACTION_NAMES.cpp_link_executable],
flag_groups = [
flag_group(
flags = [
"-fuse-ld=lld",
# We chose to use the llvm runtime, not the gcc one because it is already
# included in the clang binary
"--rtlib=compiler-rt",
"-std=c++17",
# We statically include these libc++ libraries so they do not need to be
# on a developer's machine (they can be tricky to get).
EXTERNAL_TOOLCHAIN + "/lib/libc++.a",
EXTERNAL_TOOLCHAIN + "/lib/libc++abi.a",
EXTERNAL_TOOLCHAIN + "/lib/libunwind.a",
# Dynamically Link in the other parts of glibc (not needed in glibc 2.34+)
"-lpthread",
"-lm",
"-ldl",
],
),
],
)
return [feature(
"default_flags",
enabled = True,
flag_sets = [
cxx_compile_includes,
cpp_compile_includes,
link_exe_flags,
],
)]
def _make_diagnostic_flags():
"""Here we define the flags that can be turned on via features to yield debug info."""
cxx_diagnostic = flag_set(
actions = [
ACTION_NAMES.c_compile,
ACTION_NAMES.cpp_compile,
],
flag_groups = [
flag_group(
flags = [
"--trace-includes",
"-v",
],
),
],
)
link_diagnostic = flag_set(
actions = [ACTION_NAMES.cpp_link_executable],
flag_groups = [
flag_group(
flags = [
"-Wl,--verbose",
"-v",
],
),
],
)
link_search_dirs = flag_set(
actions = [ACTION_NAMES.cpp_link_executable],
flag_groups = [
flag_group(
flags = [
"--print-search-dirs",
],
),
],
)
return [
# Running a Bazel command with --features diagnostic will cause the compilation and
# link steps to be more verbose.
feature(
"diagnostic",
enabled = False,
flag_sets = [
cxx_diagnostic,
link_diagnostic,
],
),
# Running a Bazel command with --features print_search_dirs will cause the link to fail
# but directories searched for libraries, etc will be displayed.
feature(
"print_search_dirs",
enabled = False,
flag_sets = [
link_search_dirs,
],
),
]
def _make_iwyu_flags():
"""Here we define the flags that signal whether or not to enforce IWYU."""
# https://bazel.build/docs/cc-toolchain-config-reference#features
opt_file_into_iwyu = flag_set(
actions = [
ACTION_NAMES.c_compile,
ACTION_NAMES.cpp_compile,
],
flag_groups = [
flag_group(
flags = [
# This define does not impact compilation, but it acts as a signal to the
# clang_trampoline.sh whether to maybe check the file with include-what-you-use
# A define was chosen because it is ignored by clang and IWYU, but can be
# easily found with bash.
# The clang_trampoline.sh file has a list of allowed subdirectories for which
# IWYU should be enforced, allowing us to slowly opt more and more directories
# in over time.
"-DSKIA_ENFORCE_IWYU",
],
),
],
)
return [
feature(
"skia_enforce_iwyu",
enabled = False,
flag_sets = [
opt_file_into_iwyu,
],
),
]
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