rust: add bindgen step as a meson dependency

Add bindings_rs target for generating rust bindings to target-independent
qemu C APIs.

The bindings need be created before any rust crate that uses them is
compiled.

The bindings.rs file will end up in BUILDDIR/bindings.rs and have the
same name as a target:

  ninja bindings.rs

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Link: https://lore.kernel.org/r/1be89a27719049b7203eaf2eca8bbb75b33f18d4.1727961605.git.manos.pitsidianakis@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

MAINTAINERS

@@ -4191,7 +4191,11 @@ F: docs/devel/docs.rst
 Rust build system integration
 M: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
 S: Maintained
+F: scripts/rust/
+F: rust/.gitignore
 F: rust/Kconfig
+F: rust/meson.build
+F: rust/wrapper.h
 
 Miscellaneous
 -------------

configure

@@ -2060,3 +2060,10 @@ echo ' "$@"' >>config.status
 chmod +x config.status
 
 rm -r "$TMPDIR1"
+
+if test "$rust" != disabled; then
+  echo '\nINFO: Rust bindings generation with `bindgen` might fail in some cases where'
+  echo 'the detected `libclang` does not match the expected `clang` version/target. In'
+  echo 'this case you must pass the path to `clang` and `libclang` to your build'
+  echo 'command invocation using the environment variables CLANG_PATH and LIBCLANG_PATH'
+fi

meson.build

@@ -3892,6 +3892,74 @@ common_all = static_library('common',
                             implicit_include_directories: false,
                             dependencies: common_ss.all_dependencies())
 
+if have_rust and have_system
+  rustc_args = run_command(
+    find_program('scripts/rust/rustc_args.py'),
+    '--config-headers', meson.project_build_root() / 'config-host.h',
+    capture : true,
+    check: true).stdout().strip().split()
+  rustc_args += ['-D', 'unsafe_op_in_unsafe_fn']
+  bindgen_args = [
+    '--disable-header-comment',
+    '--raw-line', '// @generated',
+    '--ctypes-prefix', 'core::ffi',
+    '--formatter', 'rustfmt',
+    '--generate-block',
+    '--generate-cstr',
+    '--impl-debug',
+    '--merge-extern-blocks',
+    '--no-doc-comments',
+    '--use-core',
+    '--with-derive-default',
+    '--no-size_t-is-usize',
+    '--no-layout-tests',
+    '--no-prepend-enum-name',
+    '--allowlist-file', meson.project_source_root() + '/include/.*',
+    '--allowlist-file', meson.project_source_root() + '/.*',
+    '--allowlist-file', meson.project_build_root() + '/.*'
+    ]
+  c_enums = [
+    'DeviceCategory',
+    'GpioPolarity',
+    'MachineInitPhase',
+    'MemoryDeviceInfoKind',
+    'MigrationPolicy',
+    'MigrationPriority',
+    'QEMUChrEvent',
+    'QEMUClockType',
+    'device_endian',
+    'module_init_type',
+  ]
+  foreach enum : c_enums
+    bindgen_args += ['--rustified-enum', enum]
+  endforeach
+  c_bitfields = [
+    'ClockEvent',
+    'VMStateFlags',
+  ]
+  foreach enum : c_bitfields
+    bindgen_args += ['--bitfield-enum', enum]
+  endforeach
+
+  # TODO: Remove this comment when the clang/libclang mismatch issue is solved.
+  #
+  # Rust bindings generation with `bindgen` might fail in some cases where the
+  # detected `libclang` does not match the expected `clang` version/target. In
+  # this case you must pass the path to `clang` and `libclang` to your build
+  # command invocation using the environment variables CLANG_PATH and
+  # LIBCLANG_PATH
+  bindings_rs = import('rust').bindgen(
+    input: 'rust/wrapper.h',
+    dependencies: common_ss.all_dependencies(),
+    output: 'bindings.rs',
+    include_directories: include_directories('.', 'include'),
+    bindgen_version: ['>=0.69.4'],
+    args: bindgen_args,
+    )
+  subdir('rust')
+endif
+
+
 feature_to_c = find_program('scripts/feature_to_c.py')
 
 if host_os == 'darwin'

rust/.gitignore

@@ -0,0 +1,3 @@
+# Ignore any cargo development build artifacts; for qemu-wide builds, all build
+# artifacts will go to the meson build directory.
+target

rust/wrapper.h

@@ -0,0 +1,47 @@
+/*
+ * QEMU System Emulator
+ *
+ * Copyright (c) 2024 Linaro Ltd.
+ *
+ * Authors: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+
+/*
+ * This header file is meant to be used as input to the `bindgen` application
+ * in order to generate C FFI compatible Rust bindings.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/module.h"
+#include "qemu-io.h"
+#include "sysemu/sysemu.h"
+#include "hw/sysbus.h"
+#include "exec/memory.h"
+#include "chardev/char-fe.h"
+#include "hw/clock.h"
+#include "hw/qdev-clock.h"
+#include "hw/qdev-properties.h"
+#include "hw/qdev-properties-system.h"
+#include "hw/irq.h"
+#include "qapi/error.h"
+#include "migration/vmstate.h"
+#include "chardev/char-serial.h"

scripts/rust/rustc_args.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+
+"""Generate rustc arguments for meson rust builds.
+
+This program generates --cfg compile flags for the configuration headers passed
+as arguments.
+
+Copyright (c) 2024 Linaro Ltd.
+
+Authors:
+ 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 logging
+
+from typing import 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 main() -> None:
+    # pylint: disable=missing-function-docstring
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-v", "--verbose", action="store_true")
+    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=[],
+    )
+    args = parser.parse_args()
+    if args.verbose:
+        logging.basicConfig(level=logging.DEBUG)
+    logging.debug("args: %s", args)
+    for header in args.config_headers:
+        for tok in generate_cfg_flags(header):
+            print(tok)
+
+
+if __name__ == "__main__":
+    main()