[RFC PATCH v4 1/7] build-sys: Add rust feature option

[Manos Pitsidianakis]

Add options for Rust in meson_options.txt, meson.build, configure to
prepare for adding Rust code in the followup commits.

`rust` is a reserved meson name, so we have to use an alternative.
`with_rust` was chosen.

A cargo_wrapper.py script is added that is heavily based on the work of
Marc-André Lureau from 2021.

https://patchew.org/QEMU/20210907121943.3498701-1-marcandre.lureau@redhat.com/

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
---
 MAINTAINERS                   |   5 +
 configure                     |  11 ++
 meson.build                   |  11 ++
 meson_options.txt             |   5 +
 scripts/cargo_wrapper.py      | 294 ++++++++++++++++++++++++++++++++++
 scripts/meson-buildoptions.sh |   6 +
 6 files changed, 332 insertions(+)
 create mode 100644 scripts/cargo_wrapper.py

diff --git a/MAINTAINERS b/MAINTAINERS
index 6725913c8b..d01bd06ab7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4226,6 +4226,11 @@ F: docs/sphinx/
 F: docs/_templates/
 F: docs/devel/docs.rst
 
+Rust build system integration
+M: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+S: Maintained
+F: scripts/cargo_wrapper.py
+
 Miscellaneous
 -------------
 Performance Tools and Tests
diff --git a/configure b/configure
index 8b6a2f16ce..180d87b9c9 100755
--- a/configure
+++ b/configure
@@ -302,6 +302,9 @@ else
   objcc="${objcc-${cross_prefix}clang}"
 fi
 
+with_rust="auto"
+with_rust_target_triple=""
+
 ar="${AR-${cross_prefix}ar}"
 as="${AS-${cross_prefix}as}"
 ccas="${CCAS-$cc}"
@@ -757,6 +760,12 @@ for opt do
   ;;
   --gdb=*) gdb_bin="$optarg"
   ;;
+  --enable-with-rust) with_rust=enabled
+  ;;
+  --disable-with-rust) with_rust=disabled
+  ;;
+  --with-rust-target-triple=*) with_rust_target_triple="$optarg"
+  ;;
   # everything else has the same name in configure and meson
   --*) meson_option_parse "$opt" "$optarg"
   ;;
@@ -1789,6 +1798,8 @@ if test "$skip_meson" = no; then
   test -n "${LIB_FUZZING_ENGINE+xxx}" && meson_option_add 
"-Dfuzzing_engine=$LIB_FUZZING_ENGINE"
   test "$plugins" = yes && meson_option_add "-Dplugins=true"
   test "$tcg" != enabled && meson_option_add "-Dtcg=$tcg"
+  test "$with_rust" != enabled && meson_option_add "-Dwith_rust=$with_rust"
+  test "$with_rust_target_triple" != "" && meson_option_add 
"-Dwith_rust_target_triple=$with_rust_target_triple"
   run_meson() {
     NINJA=$ninja $meson setup "$@" "$PWD" "$source_path"
   }
diff --git a/meson.build b/meson.build
index 2f981f936e..11b8b146da 100644
--- a/meson.build
+++ b/meson.build
@@ -290,6 +290,12 @@ foreach lang : all_languages
   endif
 endforeach
 
+cargo = not_found
+if get_option('with_rust').allowed()
+  cargo = find_program('cargo', required: get_option('with_rust'))
+endif
+with_rust = cargo.found()
+
 # default flags for all hosts
 # We use -fwrapv to tell the compiler that we require a C dialect where
 # left shift of signed integers is well defined and has the expected
@@ -2118,6 +2124,7 @@ endif
 
 config_host_data = configuration_data()
 
+config_host_data.set('CONFIG_WITH_RUST', with_rust)
 audio_drivers_selected = []
 if have_system
   audio_drivers_available = {
@@ -4243,6 +4250,10 @@ if 'objc' in all_languages
 else
   summary_info += {'Objective-C compiler': false}
 endif
+summary_info += {'Rust support':      with_rust}
+if with_rust and get_option('with_rust_target_triple') != ''
+  summary_info += {'Rust target':     get_option('with_rust_target_triple')}
+endif
 option_cflags = (get_option('debug') ? ['-g'] : [])
 if get_option('optimization') != 'plain'
   option_cflags += ['-O' + get_option('optimization')]
diff --git a/meson_options.txt b/meson_options.txt
index 0269fa0f16..3443c48001 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -371,3 +371,8 @@ option('hexagon_idef_parser', type : 'boolean', value : 
true,
 
 option('x86_version', type : 'combo', choices : ['0', '1', '2', '3', '4'], 
value: '1',
        description: 'tweak required x86_64 architecture version beyond 
compiler default')
+
+option('with_rust', type: 'feature', value: 'auto',
+       description: 'Enable Rust support')
+option('with_rust_target_triple', type : 'string', value: '',
+       description: 'Override Rust target triple')
diff --git a/scripts/cargo_wrapper.py b/scripts/cargo_wrapper.py
new file mode 100644
index 0000000000..d2c7265461
--- /dev/null
+++ b/scripts/cargo_wrapper.py
@@ -0,0 +1,294 @@
+#!/usr/bin/env python3
+
+"""Wrap cargo builds for meson integration
+
+This program builds Rust library crates and makes sure:
+ - They receive the correct --cfg compile flags from the QEMU build that calls
+   it.
+ - They receive the generated Rust bindings path so that they can copy it
+   inside their output subdirectories.
+ - Cargo puts all its build artifacts in the appropriate meson build directory.
+ - The produced static libraries are copied to the path the caller (meson)
+   defines.
+
+Copyright (c) 2020 Red Hat, Inc.
+Copyright (c) 2024 Linaro Ltd.
+
+Authors:
+ Marc-André Lureau <marcandre.lureau@redhat.com>
+ Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""
+
+
+import argparse
+import json
+import logging
+import os
+import subprocess
+import sys
+import shutil
+
+from pathlib import Path
+from typing import Any, Dict, List
+
+
+def generate_cfg_flags(header: str) -> List[str]:
+    """Converts defines from config[..].h headers to rustc --cfg flags."""
+
+    def cfg_name(name: str) -> str:
+        """Filter function for C #defines"""
+        if (
+            name.startswith("CONFIG_")
+            or name.startswith("TARGET_")
+            or name.startswith("HAVE_")
+        ):
+            return name
+        return ""
+
+    with open(header, encoding="utf-8") as cfg:
+        config = [l.split()[1:] for l in cfg if l.startswith("#define")]
+
+    cfg_list = []
+    for cfg in config:
+        name = cfg_name(cfg[0])
+        if not name:
+            continue
+        if len(cfg) >= 2 and cfg[1] != "1":
+            continue
+        cfg_list.append("--cfg")
+        cfg_list.append(name)
+    return cfg_list
+
+
+def cargo_target_dir(args: argparse.Namespace) -> Path:
+    """Place cargo's build artifacts into meson's build directory"""
+    return args.private_dir
+
+
+def manifest_path(args: argparse.Namespace) -> Path:
+    """Returns the Cargo.toml manifest path"""
+    return args.crate_dir / "Cargo.toml"
+
+
+def get_cargo_rustc(args: argparse.Namespace) -> tuple[Dict[str, Any], 
List[str]]:
+    """Returns the appropriate cargo invocation and environment"""
+
+    # See https://doc.rust-lang.org/cargo/reference/environment-variables.html
+    # Item `CARGO_ENCODED_RUSTFLAGS — A list of custom flags separated by
+    # 0x1f (ASCII Unit Separator) to pass to all compiler invocations that 
Cargo
+    # performs`
+    cfg = chr(0x1F).join(
+        [c for h in args.config_headers for c in generate_cfg_flags(h)]
+    )
+    target_dir = cargo_target_dir(args)
+    cargo_path = manifest_path(args)
+
+    cargo_cmd = [
+        "cargo",
+        "build",
+        "--target-dir",
+        str(target_dir),
+        "--manifest-path",
+        str(cargo_path),
+    ]
+    if args.target_triple:
+        cargo_cmd += ["--target", args.target_triple]
+    if args.profile == "release":
+        cargo_cmd += ["--release"]
+
+    env = os.environ
+    env["CARGO_ENCODED_RUSTFLAGS"] = cfg
+
+    return (env, cargo_cmd)
+
+
+def run_cargo(env: Dict[str, Any], cargo_cmd: List[str]) -> str:
+    """Calls cargo build invocation."""
+    envlog = " ".join([f"{k}={v}" for k, v in env.items()])
+    cmdlog = " ".join(cargo_cmd)
+    logging.debug("Running %s %s", envlog, cmdlog)
+    try:
+        out = subprocess.check_output(
+            cargo_cmd,
+            env=dict(os.environ, **env),
+            stderr=subprocess.STDOUT,
+            universal_newlines=True,
+        )
+    except subprocess.CalledProcessError as err:
+        print("Environment: " + envlog)
+        print("Command: " + cmdlog)
+        print(err.output)
+        sys.exit(1)
+
+    return out
+
+
+def get_package_name(cargo_toml_path: Path) -> str:
+    """Attempts to get package name from cargo manifest file with toml parsing 
libraries."""
+    # pylint: disable=import-outside-toplevel
+
+    try:
+        import tomllib
+    except ImportError:
+        import tomli as tomllib
+    with open(cargo_toml_path, "rb") as toml_file:
+        config = tomllib.load(toml_file)
+
+    package_name = config["package"]["name"].strip('"').replace("-", "_")
+    return package_name
+
+
+def get_package_name_json(cargo_toml_path: Path) -> str:
+    """Attempts to get package name from cargo-metadata output which has a 
standard JSON format."""
+
+    cmd = [
+        "cargo",
+        "metadata",
+        "--format-version",
+        "1",
+        "--no-deps",
+        "--manifest-path",
+        str(cargo_toml_path),
+        "--offline",
+    ]
+    try:
+        out = subprocess.check_output(
+            cmd,
+            env=os.environ,
+            stderr=subprocess.STDOUT,
+            universal_newlines=True,
+        )
+    except subprocess.CalledProcessError as err:
+        print("Command: ", " ".join(cmd))
+        print(err.output)
+        raise err
+    package_name = 
json.loads(out)["packages"][0]["name"].strip('"').replace("-", "_")
+    return package_name
+
+
+def build_lib(args: argparse.Namespace) -> None:
+    """Builds Rust lib given by command line arguments."""
+
+    logging.debug("build-lib")
+    target_dir = cargo_target_dir(args)
+    cargo_toml_path = manifest_path(args)
+
+    try:
+        # If we have tomllib or tomli, parse the .toml file
+        package_name = get_package_name(cargo_toml_path)
+    except ImportError as import_exc:
+        try:
+            # Parse the json output of cargo-metadata as a fallback
+            package_name = get_package_name_json(cargo_toml_path)
+        except Exception as exc:
+            raise exc from import_exc
+
+    liba_filename = "lib" + package_name + ".a"
+    profile_dir = args.profile
+    if args.profile == "dev":
+        profile_dir = "debug"
+
+    liba = target_dir / args.target_triple / profile_dir / liba_filename
+
+    env, cargo_cmd = get_cargo_rustc(args)
+    out = run_cargo(env, cargo_cmd)
+    logging.debug("cargo output: %s", out)
+    logging.debug("cp %s %s", liba, args.outdir)
+    shutil.copy2(liba, args.outdir)
+
+
+def main() -> None:
+    # pylint: disable=missing-function-docstring
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-v", "--verbose", action="store_true")
+    parser.add_argument(
+        "--color",
+        metavar="WHEN",
+        choices=["auto", "always", "never"],
+        default="auto",
+        help="Coloring: auto, always, never",
+    )
+    parser.add_argument(
+        "--config-headers",
+        metavar="CONFIG_HEADER",
+        action="append",
+        dest="config_headers",
+        help="paths to any configuration C headers (*.h files), if any",
+        required=False,
+        default=[],
+    )
+    parser.add_argument(
+        "--meson-build-dir",
+        metavar="BUILD_DIR",
+        help="meson.current_build_dir()",
+        type=Path,
+        dest="meson_build_dir",
+        required=True,
+    )
+    parser.add_argument(
+        "--meson-source-dir",
+        metavar="SOURCE_DIR",
+        help="meson.current_source_dir()",
+        type=Path,
+        dest="meson_build_dir",
+        required=True,
+    )
+    parser.add_argument(
+        "--crate-dir",
+        metavar="CRATE_DIR",
+        type=Path,
+        dest="crate_dir",
+        help="Absolute path that contains the manifest file of the crate to 
compile. Example: '/path/to/qemu/rust/pl011'",
+        required=True,
+    )
+    parser.add_argument(
+        "--outdir",
+        metavar="OUTDIR",
+        type=Path,
+        dest="outdir",
+        help="Destination path to copy compiled artifacts to for Meson to use. 
Example values: '/path/to/qemu/build', '.'",
+        required=True,
+    )
+    # using @PRIVATE_DIR@ is necessary for `ninja clean` to clean up rust's 
intermediate build artifacts.
+    # NOTE: at the moment cleanup doesn't work due to a bug: 
https://github.com/mesonbuild/meson/issues/7584
+    parser.add_argument(
+        "--private-dir",
+        metavar="PRIVATE_DIR",
+        type=Path,
+        dest="private_dir",
+        help="Override cargo's target directory with a meson provided private 
directory.",
+        required=True,
+    )
+    parser.add_argument(
+        "--profile", type=str, choices=["release", "dev"], required=True
+    )
+    parser.add_argument("--target-triple", type=str, required=True)
+
+    subparsers = parser.add_subparsers()
+
+    buildlib = subparsers.add_parser("build-lib")
+    buildlib.set_defaults(func=build_lib)
+
+    args = parser.parse_args()
+    if args.verbose:
+        logging.basicConfig(level=logging.DEBUG)
+    logging.debug("args: %s", args)
+
+    args.func(args)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/scripts/meson-buildoptions.sh b/scripts/meson-buildoptions.sh
index cfadb5ea86..23a24ccaa7 100644
--- a/scripts/meson-buildoptions.sh
+++ b/scripts/meson-buildoptions.sh
@@ -79,6 +79,8 @@ meson_options_help() {
   printf "%s\n" '                           auto/sigaltstack/ucontext/windows)'
   printf "%s\n" '  --with-pkgversion=VALUE  use specified string as 
sub-version of the'
   printf "%s\n" '                           package'
+  printf "%s\n" '  --with-rust-target-triple=VALUE'
+  printf "%s\n" '                           Specify Rust host target triple'
   printf "%s\n" '  --with-suffix=VALUE      Suffix for QEMU 
data/modules/config directories'
   printf "%s\n" '                           (can be empty) [qemu]'
   printf "%s\n" '  --with-trace-file=VALUE  Trace file prefix for simple 
backend [trace]'
@@ -216,6 +218,7 @@ meson_options_help() {
   printf "%s\n" '  vvfat           vvfat image format support'
   printf "%s\n" '  werror          Treat warnings as errors'
   printf "%s\n" '  whpx            WHPX acceleration support'
+  printf "%s\n" '  with-rust       Enable Rust support'
   printf "%s\n" '  xen             Xen backend support'
   printf "%s\n" '  xen-pci-passthrough'
   printf "%s\n" '                  Xen PCI passthrough support'
@@ -552,6 +555,9 @@ _meson_option_parse() {
     --enable-whpx) printf "%s" -Dwhpx=enabled ;;
     --disable-whpx) printf "%s" -Dwhpx=disabled ;;
     --x86-version=*) quote_sh "-Dx86_version=$2" ;;
+    --enable-with-rust) printf "%s" -Dwith_rust=enabled ;;
+    --disable-with-rust) printf "%s" -Dwith_rust=disabled ;;
+    --with-rust-target-triple=*) quote_sh "-Dwith_rust_target_triple=$2" ;;
     --enable-xen) printf "%s" -Dxen=enabled ;;
     --disable-xen) printf "%s" -Dxen=disabled ;;
     --enable-xen-pci-passthrough) printf "%s" -Dxen_pci_passthrough=enabled ;;
-- 
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