# Copyright 2021 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
# This file provides the Rust standard library for GN targets.
#
# For Rust targets, it either copies a prebuilt stdlib or builds a stdlib, and
# then points rustc to it with `--sysroot`.
#
# When linking it ensures the libraries (and their C library dependencies) are
# part of the linker line. If Rust drives the linking, this is redundant but if
# Clang drives the linking it is required.
#
# Part of the standard library provided here is "remap_alloc" which maps
# allocator functions to PartitionAlloc when `use_partition_alloc_as_malloc` is
# true, so that Rust and C++ use the same allocator backend.
import("//build/config/compiler/compiler.gni")
import("//build/config/coverage/coverage.gni")
import("//build/config/rust.gni")
import("//build/config/sanitizers/sanitizers.gni")
if (toolchain_has_rust) {
# List of Rust stdlib rlibs which are present in the official Rust toolchain
# we are using from the Android team. This is usually a version or two behind
# nightly. Generally this matches the toolchain we build ourselves, but if
# they differ, append or remove libraries based on the
# `use_chromium_rust_toolchain` GN variable.
#
# If the build fails due to missing symbols, it would be because of a missing
# library that needs to be added here in a newer stdlib.
stdlib_files = [
"std", # List first because it makes depfiles more debuggable (see below)
"alloc",
"cfg_if",
"compiler_builtins",
"core",
"getopts",
"hashbrown",
"panic_abort",
"rustc_demangle",
"std_detect",
"test",
"unwind",
]
if (!is_win) {
# These are no longer present in the Windows toolchain.
stdlib_files += [
"addr2line",
"gimli",
"libc",
"memchr",
"miniz_oxide",
"object",
]
if (rustc_nightly_capability) {
stdlib_files += [ "adler2" ]
} else {
stdlib_files += [ "adler" ]
}
}
if (toolchain_for_rust_host_build_tools) {
# When building proc macros, include the proc_macro crate in what should be
# copied with find_stdlib. Otherwise it is not copied since it will be
# unused.
stdlib_files += [ "proc_macro" ]
}
# Different Rust toolchains may add or remove files relative to the above
# list. That can be specified in gn args for anyone using (for instance)
# nightly or some other experimental toolchain, prior to it becoming official.
stdlib_files -= removed_rust_stdlib_libs
stdlib_files += added_rust_stdlib_libs
# rlib files which are distributed alongside Rust's prebuilt stdlib, but we
# don't need to pass to the C++ linker because they're used for specialized
# purposes.
skip_stdlib_files = [
"profiler_builtins",
"rustc_std_workspace_alloc",
"rustc_std_workspace_core",
"rustc_std_workspace_std",
]
config("stdlib_dependent_libs") {
# TODO(crbug.com/40264561): These should really be `libs`, however that
# breaks. Normally, we specify lib files with the `.lib` suffix but
# then when rustc links an EXE, it invokes lld-link with `.lib.lib`
# instead.
#
# Omitting the `.lib` suffix breaks linking as well, when clang drives
# the linking step of a C++ EXE that depends on Rust.
if (is_win) {
# The libc crate tries to link in the Windows CRT, but we specify the CRT
# library ourselves in //build/config/win:dynamic_crt and
# //build/config/win:static_crt because Rustc does not allow us to specify
# using the debug CRT: https://github.com/rust-lang/rust/issues/39016
#
# As such, we have disabled all #[link] directives from the libc crate,
# and we need to add any non-CRT libs here.
ldflags = [ "legacy_stdio_definitions.lib" ]
}
}
config("stdlib_public_dependent_libs") {
# TODO(crbug.com/40264561): These should really be `libs`, however that
# breaks. Normally, we specify lib files with the `.lib` suffix but
# then when rustc links an EXE, it invokes lld-link with `.lib.lib`
# instead.
#
# Omitting the `.lib` suffix breaks linking as well, when clang drives
# the linking step of a C++ EXE that depends on Rust.
if (is_win) {
# These libs provide functions that are used by the stdlib. Rust crates
# will try to link them in with #[link] directives. However these don't
# get propagated to the linker if Rust isn't driving the linking (a C++
# target that depends on a Rust rlib). So these need to be specified
# explicitly.
ldflags = [
"advapi32.lib",
"bcrypt.lib",
"kernel32.lib",
"ntdll.lib",
"synchronization.lib",
"userenv.lib",
"ws2_32.lib",
]
}
# From rust/library/std/src/sys/unix/mod.rs.
#
# libs = [ "System" ] (meaning /usr/lib/libSystem.B.dylib) is intentionally
# omitted here on Apple platforms, because the linker driver is responsible
# for adding it, much like libc on most other POSIX platforms. It can be
# ordering-sensitive, and including it here can alter its order relative to
# other libraries. https://crbug.com/367764848 is an example of a bug caused
# by specifying libSystem too early.
#
# TODO(danakj): We should generate this list somehow when building or
# rolling the Rust toolchain?
if (is_android) {
libs = [ "dl" ]
} else if (target_os == "freebsd") {
libs = [
"execinfo",
"pthread",
]
} else if (target_os == "netbsd") {
libs = [
"rt",
"pthread",
]
} else if (is_ios) {
libs = [ "objc" ]
frameworks = [
"Security.framework",
"Foundation.framework",
]
} else if (is_fuchsia) {
libs = [
"zircon",
"fdio",
]
}
}
# Construct sysroots for rustc invocations to better control what libraries
# are linked. We have two: one with copied prebuilt libraries, and one with
# our locally-built std. Both reside in root_out_dir: we must only have one of
# each per GN toolchain anyway.
sysroot_lib_subdir = "lib/rustlib/$rust_abi_target/lib"
if (!rust_prebuilt_stdlib) {
local_rustc_sysroot = "$root_out_dir/local_rustc_sysroot"
# All std targets starting with core build with our sysroot. It starts empty
# and is incrementally built. The directory must exist at the start.
generated_file("empty_sysroot_for_std_build") {
outputs = [ "$local_rustc_sysroot/$sysroot_lib_subdir/.empty" ]
contents = ""
visibility = [ ":*" ]
}
# Target to be depended on by std build targets. Creates the initially empty
# sysroot.
group("std_build_deps") {
deps = [ ":empty_sysroot_for_std_build" ]
public_configs = [ ":local_stdlib_sysroot" ]
visibility = [ "rules:*" ]
}
profiler_builtins_crates = [
"core",
"compiler_builtins",
"profiler_builtins",
]
# When using instrumentation, profiler_builtins and its deps must be built
# before other std crates. Other crates depend on this target so they are
# built in the right order.
group("profiler_builtins_group") {
deps = []
foreach(libname, profiler_builtins_crates) {
deps += [ "rules:$libname" ]
}
visibility = [ "rules:*" ]
}
config("local_stdlib_sysroot") {
sysroot = rebase_path(local_rustc_sysroot, root_build_dir)
rustflags = [ "--sysroot=$sysroot" ]
visibility = [ ":*" ]
}
# Builds and links against the Rust stdlib. Both Rust and C++ targets should
# depend on this, as it provides the path to the library and includes the
# allocator hooks.
group("std") {
assert(toolchain_has_rust,
"Some C++ target is depending on Rust code even though " +
"toolchain_has_rust=false. Usually this would mean" +
"a NaCl target is depending on Rust, as there's no Rust " +
"toolchain targetting NaCl.")
all_dependent_configs = [
":stdlib_public_dependent_libs",
":local_stdlib_sysroot",
":stdlib_dependent_libs",
]
deps = []
foreach(libname, stdlib_files + skip_stdlib_files) {
deps += [ "rules:$libname" ]
}
}
if (enable_cpp_api_from_rust) {
group("std_bindings") {
deps = [ ":std" ]
public_deps = []
foreach(libname, stdlib_files + skip_stdlib_files) {
public_deps += [ "rules:${libname}_bindings" ]
}
}
}
} else {
action("find_stdlib") {
# Collect prebuilt Rust libraries from toolchain package and copy to a
# known location.
#
# The Rust toolchain contains prebuilt rlibs for the standard library and
# its dependencies. However, they have unstable names: an unpredictable
# metadata hash is appended to the known crate name.
#
# We must depend on these rlibs explicitly when rustc is not in charge of
# linking. However, it is difficult to construct GN rules to do so when
# the names can't be known statically.
#
# This action copies the prebuilt rlibs to a known location, removing the
# metadata part of the name. In the process it verifies we have all the
# libraries we expect and none that we don't. A depfile is generated so
# this step is re-run when any libraries change. The action script
# additionally verifies rustc matches the expected version, which is
# unrelated but this is a convenient place to do so.
#
# The action refers to `stdlib_files`, `skip_stdlib_files`, and the
# associated //build/config/rust.gni vars `removed_rust_stdlib_libs` and
# `added_rust_stdlib_libs` for which rlib files to expect.
# `extra_sysroot_libs` is also used to copy non-std libs, if any.
script = "find_std_rlibs.py"
depfile = "$target_out_dir/stdlib.d"
out_libdir = rebase_path(target_out_dir, root_build_dir)
out_depfile = rebase_path(depfile, root_build_dir)
# For the rustc sysroot we must include even the rlibs we don't pass to
# the C++ linker.
all_stdlibs_to_copy = stdlib_files + skip_stdlib_files
args = [
"--rust-bin-dir",
rebase_path("${rust_sysroot}/bin", root_build_dir),
"--output",
out_libdir,
"--depfile",
out_depfile,
# Due to limitations in Ninja's handling of .d files, we have to pick
# *the first* of our outputs. To make diagnostics more obviously
# related to the Rust standard library, we ensure libstd.rlib is first.
"--depfile-target",
stdlib_files[0],
# Create a dependency on the rustc version so this action is re-run when
# it changes. This argument is not actually read by the script.
"--rustc-revision",
rustc_revision,
]
if (extra_sysroot_libs != []) {
args += [
"--extra-libs",
string_join(",", extra_sysroot_libs),
]
}
args += [
"--target",
rust_abi_target,
]
outputs = []
foreach(lib, all_stdlibs_to_copy) {
outputs += [ "$target_out_dir/lib$lib.rlib" ]
}
foreach(lib, extra_sysroot_libs) {
outputs += [ "$target_out_dir/$lib" ]
}
visibility = [ ":*" ]
}
prebuilt_rustc_sysroot = "$root_out_dir/prebuilt_rustc_sysroot"
copy("prebuilt_rustc_copy_to_sysroot") {
assert(enable_rust,
"Some C++ target is including Rust code even though " +
"enable_rust=false")
deps = [ ":find_stdlib" ]
sources = get_target_outputs(":find_stdlib")
outputs =
[ "$prebuilt_rustc_sysroot/$sysroot_lib_subdir/{{source_file_part}}" ]
visibility = [ ":*" ]
}
config("prebuilt_stdlib_sysroot") {
# Match the output directory of :prebuilt_rustc_copy_to_sysroot
sysroot = rebase_path(prebuilt_rustc_sysroot, root_build_dir)
rustflags = [ "--sysroot=$sysroot" ]
visibility = [ ":*" ]
}
config("prebuilt_stdlib_libs") {
ldflags = []
lib_dir = rebase_path("$prebuilt_rustc_sysroot/$sysroot_lib_subdir",
root_build_dir)
# We're unable to make these files regular gn dependencies because
# they're prebuilt. Instead, we'll pass them in the ldflags. This doesn't
# work for all types of build because ldflags propagate differently from
# actual dependencies and therefore can end up in different targets from
# the remap_alloc.cc above. For example, in a component build, we might
# apply the remap_alloc.cc file and these ldlags to shared object A,
# while shared object B (that depends upon A) might get only the ldflags
# but not remap_alloc.cc, and thus the build will fail. There is
# currently no known solution to this for the prebuilt stdlib - this
# problem does not apply with configurations where we build the stdlib
# ourselves, which is what we'll use in production.
foreach(lib, stdlib_files) {
this_file = "$lib_dir/lib$lib.rlib"
ldflags += [ this_file ]
}
visibility = [ ":*" ]
}
group("std") {
all_dependent_configs = [
":prebuilt_stdlib_libs",
":stdlib_public_dependent_libs",
]
deps = [ ":prebuilt_rustc_copy_to_sysroot" ]
}
}
}