Pada artikel sebelumnya, kita berbicara tentang bagaimana menghindari penulisan ulang perpustakaan di Rust saat Anda tidak membutuhkannya. Tetapi bagaimana dengan saat Anda benar-benar membutuhkannya?

Dalam kebanyakan bahasa, Anda harus menulis ulang seluruh pustaka dari awal, dan hasil pertama akan muncul menjelang akhir proyek. Porta ini cenderung mahal dan rawan kesalahan, dan sering gagal di tengah jalan. Joel Spolsky menjelaskan ini jauh lebih baik daripada yang saya lakukan dalam artikel tentang mengapa pengerjaan ulang lengkap adalah ide yang buruk .

Namun, Rust memiliki twist mematikan dalam hal hal-hal semacam ini. Itu dapat memanggil kode C tanpa overhead (yaitu lingkungan P / Invoke di C #), dan menampilkan fungsi yang dapat digunakan di C sama seperti fungsi lain di C. Ini membuka pintu ke pendekatan alternatif:

Pustaka port ke fungsi Rust satu per satu.

Catatan

Kode dalam artikel ini tersedia di GitHub . Jangan ragu untuk mampir untuk meminjam kode atau inspirasi.

Jika Anda menemukan artikel bermanfaat atau melihat kesalahan, beri tahu saya di pelacak bug blog !

Mulai

Sebelum Anda dapat melakukan apa pun, Anda perlu membuat proyek baru. Saya memiliki template yang menginstal CI dan lisensi untuk pembuatan kargo .

$ cargo generate --git https://github.com/Michael-F-Bryan/github-template --name tinyvm-rs
$ cd tinyvm-rs && tree
tree -I 'vendor|target'
.
├── Cargo.toml
├── LICENSE_APACHE.md
├── LICENSE_MIT.md
├── README.md
├── .travis.yml
└── src
    └── lib.rs

1 directory, 6 files

Tantangan nyata pertama kami adalah membangun perpustakaan yang ingin kami porting dan mencari tahu sedikit.

Dalam hal ini, kami memporting jakogut / tinyvm ,

TinyVM adalah mesin virtual kecil, cepat, dan ringan yang ditulis dalam ANSI C.

Untuk memudahkan referensi di masa mendatang, mari tambahkan repositori sebagai submodul ke proyek kita.

$ git submodule add https://github.com/jakogut/tinyvm vendor/tinyvm

Sekarang mari kita lihat kode sumbernya. Sebagai permulaan, README.mdinstruksi perakitan.

TinyVM adalah mesin virtual terkecil. Penggunaan memori rendah, sedikit kode dan sedikit kode biner.

Pembangunan dilakukan pada sistem mirip UNIX dengan make dan GCC.

Tidak ada ketergantungan eksternal, pertahankan pustaka C standar.

Build dilakukan dengan make atau make ulang.

Untuk membuat versi debug, tambahkan DEBUG = yes setelah make. Untuk membangun biner dengan profiling diaktifkan, tambahkan PROFILE = yes setelah make.

Anda dapat menghubungi saya di joseph.kogut (at) gmail.com

(penekanan ditambahkan)

Oke, mari kita lihat di direktori tinyvmdan lihat apakah build sudah berfungsi .

$ cd vendor/tinyvm
$ make
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm_program.c -o libtvm/tvm_program.o
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm_lexer.c -o libtvm/tvm_lexer.o
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm.c -o libtvm/tvm.o
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm_htab.c -o libtvm/tvm_htab.o
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm_memory.c -o libtvm/tvm_memory.o
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm_preprocessor.c -o libtvm/tvm_preprocessor.o
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm_parser.c -o libtvm/tvm_parser.o
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm_file.c -o libtvm/tvm_file.o
ar rcs lib/libtvm.a libtvm/tvm_program.o libtvm/tvm_lexer.o libtvm/tvm.o libtvm/tvm_htab.o libtvm/tvm_memory.o libtvm/tvm_preprocessor.o libtvm/tvm_parser.o libtvm/tvm_file.o
clang src/tvmi.c -ltvm -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -Llib/ -o bin/tvmi
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c tdb/main.c -o tdb/main.o
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c tdb/tdb.c -o tdb/tdb.o
clang tdb/main.o tdb/tdb.o -ltvm -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -Llib/ -o bin/tdb

Saya sangat suka ketika perpustakaan C dikompilasi langsung dari kotak tanpa harus menginstal paket acak *-devatau mengutak-atik sistem build.

Sayangnya, pustaka tidak berisi pengujian apa pun, jadi kami tidak dapat (segera) memastikan bahwa masing-masing fungsi diterjemahkan dengan benar, tetapi pustaka berisi contoh penerjemah yang dapat kami gunakan untuk menjelajahi fungsionalitas tingkat tinggi.

Jadi, kami tahu bahwa kami dapat membuatnya dari baris perintah tanpa banyak kerumitan. Sekarang kita perlu memastikan bahwa peti kita tinyvmdapat mengumpulkan semuanya secara terprogram.

Di sinilah skrip build masuk. Strategi kami adalah agar Rust crate menggunakan skrip build build.rsdan crate ccuntuk menjalankan perintah yang setara ke panggilan kamimake... Dari sana, kita dapat terhubung ke libtvmdari Rust sama seperti perpustakaan asli lainnya.

Anda perlu menambahkan peti ccsebagai ketergantungan.

$ cargo add --build cc
    Updating 'https://github.com/rust-lang/crates.io-index' index
      Adding cc v1.0.47 to build-dependencies

Dan juga pastikan untuk build.rsmengkompilasi dari sumber libtvm.

// build.rs

use cc::Build;
use std::path::Path;

fn main() {
    let tinyvm = Path::new("vendor/tinyvm");
    let include = tinyvm.join("include");
    let src = tinyvm.join("libtvm");

    Build::new()
        .warnings(false)
        .file(src.join("tvm_file.c"))
        .file(src.join("tvm_htab.c"))
        .file(src.join("tvm_lexer.c"))
        .file(src.join("tvm_memory.c"))
        .file(src.join("tvm_parser.c"))
        .file(src.join("tvm_preprocessor.c"))
        .file(src.join("tvm_program.c"))
        .file(src.join("tvm.c"))
        .include(&include)
        .compile("tvm");
}

Catatan

Jika Anda telah melihat dokumentasi peti cc, Anda mungkin telah memperhatikan metode Build::files()yang menerima iterator jalur. Kami secara terprogram dapat menemukan semua file *.cdi dalamnya vendor/tinyvm/libtvm, tetapi karena kami mem-porting kode satu fungsi pada satu waktu, jauh lebih mudah untuk menghapus panggilan individual .file()saat kami porting.

Kami juga membutuhkan cara untuk memberi tahu Rust dari fungsi apa yang dapat dipanggil libtvm. Ini biasanya dilakukan dengan menulis definisi untuk setiap fungsi di blok eksternal , tetapi untungnya ada alat bernama bindgen yang dapat membaca file header C-style dan menghasilkan definisi untuk kita.

Mari buat binding dari vendor/tinyvm/include/tvm/tvm.h.

$ cargo install bindgen
$ bindgen vendor/tinyvm/include/tvm/tvm.h -o src/ffi.rs
$ wc --lines src/ffi.rs
992 src/ffi.rs

Anda perlu menambahkan modul ke peti kami ffi.

// src/lib.rs

#[allow(non_camel_case_types, non_snake_case)]
pub mod ffi;

Melihat direktori src/di tinyvm, kami menemukan kode sumber untuk interpreter tinyvm.

// vendor/tinyvm/src/tvmi.c

#include <stdlib.h>
#include <stdio.h>

#include <tvm/tvm.h>

int main(int argc, char **argv)
{
	struct tvm_ctx *vm = tvm_vm_create();

	if (vm != NULL && tvm_vm_interpret(vm, argv[1]) == 0)
		tvm_vm_run(vm);

	tvm_vm_destroy(vm);

	return 0;
}

Ini sangat sederhana. Yang sangat bagus mengingat kami akan menggunakan penerjemah ini sebagai salah satu contoh kami.

Untuk saat ini, mari terjemahkan langsung ke Rust dan taruh di direktori examples/.

// examples/tvmi.rs

use std::{env, ffi::CString};
use tinyvm::ffi;

fn main() {
    let filename = CString::new(env::args().nth(1).unwrap()).unwrap();
    // cast away the `const` because that's what libtvm expects
    let filename = filename.as_ptr() as *mut _;

    unsafe {
        let vm = ffi::tvm_vm_create();

        if !vm.is_null() && ffi::tvm_vm_interpret(vm, filename) == 0 {
            ffi::tvm_vm_run(vm);
        }

        ffi::tvm_vm_destroy(vm);
    }
}

Sebagai pemeriksaan, kami juga dapat memulai mesin virtual dan memastikan semuanya berfungsi.

$ cargo run --example tvmi -- vendor/tinyvm/programs/tinyvm/fact.vm
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/examples/tvmi vendor/tinyvm/programs/tinyvm/fact.vm`
1
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362880
3628800

Kelas!

Buah gantung rendah

Saat Anda memulai dengan sesuatu seperti ini, Anda tergoda untuk menyelami fitur-fitur terpenting dan memigrasikannya terlebih dahulu. Cobalah untuk menahan dorongan ini. Anda dapat dengan mudah menggigit lebih dari yang dapat Anda kunyah dan berakhir dengan membuang-buang waktu atau menurunkan semangat Anda dan membuat Anda menyerah.

Sebaliknya, mari cari yang paling sederhana.

$ ls libtvm
tvm.c  tvm_file.c  tvm_htab.c  tvm_lexer.c  tvm_memory.c  tvm_parser.c
tvm_preprocessor.c  tvm_program.c

File ini tvm_htab.terlihat menjanjikan. Saya cukup yakin itu htabsingkatan dari "tabel hash" dan pustaka standar Rust sudah berisi implementasi berkualitas tinggi. Kita harus bisa mengubahnya dengan cukup mudah.

Mari kita lihat file header tvm_htab.hdan periksa apa yang kita hadapi.

// vendor/tinyvm/include/tvm/tvm_htab.h

#ifndef TVM_HTAB_H_
#define TVM_HTAB_H_

#define KEY_LENGTH 64
#define HTAB_SIZE 4096

struct tvm_htab_node {
	char *key;
	int value;
	void *valptr;
	struct tvm_htab_node *next;
};

struct tvm_htab_ctx {
	unsigned int num_nodes;
	unsigned int size;
	struct tvm_htab_node **nodes;
};

struct tvm_htab_ctx *tvm_htab_create();
void tvm_htab_destroy(struct tvm_htab_ctx *htab);

int tvm_htab_add(struct tvm_htab_ctx *htab, const char *key, int value);
int tvm_htab_add_ref(struct tvm_htab_ctx *htab,
	const char *key, const void *valptr, int len);
int tvm_htab_find(struct tvm_htab_ctx *htab, const char *key);
char *tvm_htab_find_ref(struct tvm_htab_ctx *htab, const char *key);

#endif

Terlihat cukup mudah untuk diterapkan. Satu-satunya masalah adalah definisi tvm_htab_ctxdan tvm_htab_nodedisertakan dalam file header, yang berarti bahwa beberapa kode dapat mengakses internal tabel hash secara langsung, daripada melalui antarmuka yang dipublikasikan.

Kita dapat memeriksa apakah ada yang memiliki akses ke internal tabel hash dengan memindahkan sementara definisi struktur tvm_htab.cdan melihat apakah semuanya masih terkompilasi.

diff --git a/include/tvm/tvm_htab.h b/include/tvm/tvm_htab.h
index 9feb7a9..e7346b7 100644
--- a/include/tvm/tvm_htab.h
+++ b/include/tvm/tvm_htab.h
@@ -4,18 +4,8 @@
 #define KEY_LENGTH 64
 #define HTAB_SIZE 4096

-struct tvm_htab_node {
-       char *key;
-       int value;
-       void *valptr;
-       struct tvm_htab_node *next;
-};
-
-struct tvm_htab_ctx {
-       unsigned int num_nodes;
-       unsigned int size;
-       struct tvm_htab_node **nodes;
-};
+struct tvm_htab_node;
+struct tvm_htab_ctx;

 struct tvm_htab_ctx *tvm_htab_create();
 void tvm_htab_destroy(struct tvm_htab_ctx *htab);

Dan kemudian jalankan lagi make:

$ make
make
clang -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -c libtvm/tvm_htab.c -o libtvm/tvm_htab.o
ar rcs lib/libtvm.a libtvm/tvm_program.o libtvm/tvm_lexer.o libtvm/tvm.o libtvm/tvm_htab.o libtvm/tvm_memory.o libtvm/tvm_preprocessor.o libtvm/tvm_parser.o libtvm/tvm_file.o
clang src/tvmi.c -ltvm -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -Llib/ -o bin/tvmi
clang tdb/main.o tdb/tdb.o -ltvm -Wall -pipe -Iinclude/ -std=gnu11 -Werror -pedantic -pedantic-errors -O3 -Llib/ -o bin/tdb

Sepertinya semuanya masih berfungsi, sekarang kita memulai fase kedua; kami membuat serangkaian fungsi identik yang digunakan di bawah kap HashMap<K, V>.

Membatasi diri kita pada sebuah rintisan seminimal mungkin, kita mendapatkan:

// src/htab.rs

use std::{
    collections::HashMap,
    ffi::CString,
    os::raw::{c_char, c_int, c_void},
};

#[derive(Debug, Default, Clone, PartialEq)]
pub struct HashTable(pub(crate) HashMap<CString, Item>);

#[derive(Debug, Clone, PartialEq)]
pub(crate) struct Item {
    // not sure what to put here yet
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_create() -> *mut HashTable {
    unimplemented!()
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_destroy(htab: *mut HashTable) {
    unimplemented!()
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_add(
    htab: *mut HashTable,
    key: *const c_char,
    value: c_int,
) -> c_int {
    unimplemented!()
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_add_ref(
    htab: *mut HashTable,
    key: *const c_char,
    value_ptr: *mut c_void,
    length: c_int,
) -> c_int {
    unimplemented!()
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_find(
    htab: *mut HashTable,
    key: *const c_char,
) -> c_int {
    unimplemented!()
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_find_ref(
    htab: *mut HashTable,
    key: *const c_char,
) -> *mut c_char {
    unimplemented!()
}

Anda juga perlu mendeklarasikan modul htabdan mengekspor kembali fungsinya dari lib.rs.

// src/lib.rs

mod htab;
pub use htab::*;

Sekarang kita perlu memastikan bahwa aslinya tvm_htab.ctidak dikompilasi atau ditautkan ke perpustakaan akhir, jika tidak, linker akan menemui kita dengan dinding kesalahan simbol duplikat.

Dinding kesalahan yang mengulang simbol

error: linking with `/usr/bin/clang` failed: exit code: 1
  |
  = note: "/usr/bin/clang" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.17q5thi94e1eoj5i.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.19e8sqirbm56nu8g.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.1g6ljku8dwzpfvhi.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.1h5e5mxmiptpb7iz.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.1herotdop66zv9ot.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.1qbfxpvgd885u6o.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.21psdg8ni4vgdrzk.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.2albhpxlxxvc0ccu.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.2btm2dc9rhjhhna1.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.2kct5ftnkrqqr0mf.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.2lwgg3uosup4mkh0.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.2xduj46e9sw5vuan.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.35h8y7f23ua1qnz0.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.3cgfdtku63ltd8oc.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.3ot768hzkzzy7r76.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.3u2xnetcch8f2o02.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.4ldrdjvfzk58myrv.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.4omnum6bdjqsrq8b.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.4s8ch4ccmewulj22.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.4syl3x2rb8328h8x.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.532awiysf0h9r50f.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.5b2qwmmtc5pvnbh.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.dfjs079cp9si4o5.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.qxp6yb2gjpj0v6n.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.xz7ld20yvprst1r.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.z35ukhvchmmby1c.rcgu.o" "-o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.1d7wvlwdjap8p3g4.rcgu.o" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs" "-L" "/home/michael/Documents/tinyvm-rs/target/debug/deps" "-L" "/home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out" "-L" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-Wl,--whole-archive" "-ltvm" "-Wl,--no-whole-archive" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libtest-a39a3e9a77b17f55.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libterm-97a69cd310ff0925.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgetopts-66a42b1d94e3e6f9.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunicode_width-dd7761d848144e0d.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_std-f722acdb78755ba0.rlib" "-Wl,--start-group" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-974c3c08f6def4b3.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-eb49676f33a2c8a6.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-7ae0446feecc60f2.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-2de299b65d7f5721.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libbacktrace-64514775bc06309a.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libbacktrace_sys-1ed8aa185c63b9a5.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-a839df87f563fba5.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-8e726bdc2018d836.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-5285f42cbadf207d.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-b0362d20f8aa58fa.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-f3dd7051708453a4.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-83744846c43307ce.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-d5565a3a0f4cfe21.rlib" "-Wl,--end-group" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-ea790e85415e3bbf.rlib" "-Wl,-Bdynamic" "-ldl" "-lrt" "-lpthread" "-lgcc_s" "-lc" "-lm" "-lrt" "-lpthread" "-lutil" "-lutil" "-fuse-ld=lld"
  = note: ld.lld: error: duplicate symbol: tvm_htab_create
          >>> defined at htab.rs:14 (src/htab.rs:14)
          >>>            /home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.5b2qwmmtc5pvnbh.rcgu.o:(tvm_htab_create)
          >>> defined at tvm_htab.c:23 (vendor/tinyvm/libtvm/tvm_htab.c:23)
          >>>            tvm_htab.o:(.text.tvm_htab_create+0x0) in archive /home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out/libtvm.a

          ld.lld: error: duplicate symbol: tvm_htab_destroy
          >>> defined at htab.rs:17 (src/htab.rs:17)
          >>>            /home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.5b2qwmmtc5pvnbh.rcgu.o:(tvm_htab_destroy)
          >>> defined at tvm_htab.c:35 (vendor/tinyvm/libtvm/tvm_htab.c:35)
          >>>            tvm_htab.o:(.text.tvm_htab_destroy+0x0) in archive /home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out/libtvm.a

          ld.lld: error: duplicate symbol: tvm_htab_add_ref
          >>> defined at htab.rs:29 (src/htab.rs:29)
          >>>            /home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.5b2qwmmtc5pvnbh.rcgu.o:(tvm_htab_add_ref)
          >>> defined at tvm_htab.c:160 (vendor/tinyvm/libtvm/tvm_htab.c:160)
          >>>            tvm_htab.o:(.text.tvm_htab_add_ref+0x0) in archive /home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out/libtvm.a

          ld.lld: error: duplicate symbol: tvm_htab_add
          >>> defined at htab.rs:20 (src/htab.rs:20)
          >>>            /home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.5b2qwmmtc5pvnbh.rcgu.o:(tvm_htab_add)
          >>> defined at tvm_htab.c:147 (vendor/tinyvm/libtvm/tvm_htab.c:147)
          >>>            tvm_htab.o:(.text.tvm_htab_add+0x0) in archive /home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out/libtvm.a

          ld.lld: error: duplicate symbol: tvm_htab_find
          >>> defined at htab.rs:39 (src/htab.rs:39)
          >>>            /home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.5b2qwmmtc5pvnbh.rcgu.o:(tvm_htab_find)
          >>> defined at tvm_htab.c:189 (vendor/tinyvm/libtvm/tvm_htab.c:189)
          >>>            tvm_htab.o:(.text.tvm_htab_find+0x0) in archive /home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out/libtvm.a

          ld.lld: error: duplicate symbol: tvm_htab_find_ref
          >>> defined at htab.rs:47 (src/htab.rs:47)
          >>>            /home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-599d57f523fdb1a4.5b2qwmmtc5pvnbh.rcgu.o:(tvm_htab_find_ref)
          >>> defined at tvm_htab.c:199 (vendor/tinyvm/libtvm/tvm_htab.c:199)
          >>>            tvm_htab.o:(.text.tvm_htab_find_ref+0x0) in archive /home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out/libtvm.a
          clang: error: linker command failed with exit code 1 (use -v to see invocation)


error: aborting due to previous error

error: could not compile `tinyvm`.

Cara mengatasinya sebenarnya cukup sederhana.

diff --git a/build.rs b/build.rs
index 6f274c8..af9d467 100644
--- a/build.rs
+++ b/build.rs
@@ -9,7 +9,6 @@ fn main() {
     Build::new()
         .warnings(false)
         .file(src.join("tvm_file.c"))
-        .file(src.join("tvm_htab.c"))
         .file(src.join("tvm_lexer.c"))
         .file(src.join("tvm_memory.c"))
         .file(src.join("tvm_parser.c"))

Dan mencoba menjalankan contoh tvmilagi macet, seperti yang Anda harapkan dari program yang lengkap unimplemented!().

$ cargo run --example tvmi -- vendor/tinyvm/programs/tinyvm/fact.vm
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/examples/tvmi vendor/tinyvm/programs/tinyvm/fact.vm`
thread 'main' panicked at 'not yet implemented', src/htab.rs:14:57
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

Saat menambahkan dukungan FFI untuk tipe baru, tempat termudah untuk memulai adalah dengan konstruktor dan destruktor.

Kode Info C hanya dapat mengakses tabel hash kita melalui sebuah pointer, jadi kita perlu mengalokasikan salah satunya di heap dan kemudian mentransfer kepemilikan objek heap yang dialokasikan ke pemanggil.

// src/htab.rs

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_create() -> *mut HashTable {
    let hashtable = Box::new(HashTable::default());
    Box::into_raw(hashtable)
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_destroy(htab: *mut HashTable) {
    if htab.is_null() {
        // nothing to free
        return;
    }

    let hashtable = Box::from_raw(htab);
    // explicitly destroy the hashtable
    drop(hashtable);
}

Peringatan

Penting bahwa pemanggil HashTablehanya mematikan dengan fungsinya tvm_htab_destroy ()!

Jika tidak, dan malah mencoba menelepon free()secara langsung, hampir pasti kita akan mengalami situasi yang buruk. Paling-paling, ini akan menyebabkan kebocoran memori yang besar, tetapi sangat mungkin juga bahwa Boxdi Rust kami tidak menggunakan kelompok yang sama itu malloc()dan free (), yang berarti bahwa pelepasan objek Rust dari C dapat merusak tumpukan dan membiarkannya dalam keadaan rusak.

Menambahkan item ke hashmap hampir semudah diimplementasikan.

// src/hmap.rs

#[derive(Debug, Clone, PartialEq)]
pub(crate) struct Item {
    /// An integer value.
    value: c_int,
    /// An opaque value used with [`tvm_htab_add_ref()`].
    ///
    /// # Safety
    ///
    /// Storing the contents of a `void *` in a `Vec<u8>` *would* normally
    /// result in alignment issues, but we've got access to the `libtvm` source
    /// code and know it will only ever store `char *` strings.
    opaque_value: Vec<u8>,
}

impl Item {
    pub(crate) fn integer(value: c_int) -> Item {
        Item {
            value,
            opaque_value: Vec::new(),
        }
    }

    pub(crate) fn opaque<V>(opaque_value: V) -> Item
    where
        V: Into<Vec<u8>>,
    {
        Item {
            value: 0,
            opaque_value: opaque_value.into(),
        }
    }

    pub(crate) fn from_void(pointer: *mut c_void, length: c_int) -> Item {
        // we need to create an owned copy of the value
        let opaque_value = if pointer.is_null() {
            Vec::new()
        } else {
            unsafe {
                std::slice::from_raw_parts(pointer as *mut u8, length as usize)
                    .to_owned()
            }
        };

        Item::opaque(opaque_value)
    }
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_add(
    htab: *mut HashTable,
    key: *const c_char,
    value: c_int,
) -> c_int {
    let hashtable = &mut *htab;
    let key = CStr::from_ptr(key).to_owned();

    hashtable.0.insert(key, Item::integer(value));

    // the only time insertion can fail is if allocation fails. In that case
    // we'll abort the process anyway, so if this function returns we can
    // assume it was successful (0 = success).
    0
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_add_ref(
    htab: *mut HashTable,
    key: *const c_char,
    value_ptr: *mut c_void,
    length: c_int,
) -> c_int {
    let hashtable = &mut *htab;
    let key = CStr::from_ptr(key).to_owned();

    hashtable.0.insert(key, Item::from_void(value_ptr, length));

    0
}

, CString, String, -, *const c_char , String Rust , UTF-8.

, CStr &str, String , ASCII, , unwrap(), CString.

Dua fungsi *_find()dapat didelegasikan langsung ke fungsi internal HashMap<CString, Item>.

Satu-satunya tempat untuk berhati-hati adalah memastikan nilai yang benar dikembalikan saat elemen tidak dapat ditemukan. Dalam hal ini, melihat tvm_htab.ckita dapat melihat apa yang tvm_htab_find()kembali −1dan yang tvm_htab_find_ref()kembali NULL.

// src/hmap.rs

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_find(
    htab: *mut HashTable,
    key: *const c_char,
) -> c_int {
    let hashtable = &mut *htab;
    let key = CStr::from_ptr(key);

    match hashtable.get(key) {
        Some(item) => item.value,
        None => -1,
    }
}

#[no_mangle]
pub unsafe extern "C" fn tvm_htab_find_ref(
    htab: *mut HashTable,
    key: *const c_char,
) -> *mut c_char {
    let hashtable = &mut *htab;
    let key = CStr::from_ptr(key);

    match hashtable.0.get(key) {
        Some(item) => item.value_ptr as *mut c_char,
        None => ptr::null_mut(),
    }
}

Sekarang setelah kita benar-benar menerapkan fungsionalitas stub, semuanya akan berfungsi kembali.

Cara termudah untuk menguji ini adalah dengan menjalankan contoh kami.

cargo run --example tvmi -- vendor/tinyvm/programs/tinyvm/fact.vm
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/examples/tvmi vendor/tinyvm/programs/tinyvm/fact.vm`
1
2
6
24
120
720
5040
40320
362880
3628800

Dan untuk mengecek ulang, kita dapat menjalankannya valgrinduntuk memastikan tidak ada kebocoran memori atau apapun yang rumit dengan pointer.

$ valgrind target/debug/examples/tvmi vendor/tinyvm/programs/tinyvm/fact.vm
==1492== Memcheck, a memory error detector
==1492== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==1492== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==1492== Command: target/debug/examples/tvmi vendor/tinyvm/programs/tinyvm/fact.vm
==1492==
1
2
6
24
120
720
5040
40320
362880
3628800
==1492==
==1492== HEAP SUMMARY:
==1492==     in use at exit: 0 bytes in 0 blocks
==1492==   total heap usage: 270 allocs, 270 frees, 67,129,392 bytes allocated
==1492==
==1492== All heap blocks were freed -- no leaks are possible
==1492==
==1492== For lists of detected and suppressed errors, rerun with: -s
==1492== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Keberhasilan!

Implementasi preprocessing data

Mesin virtual tinyvmmenggunakan bentuk assembler yang disederhanakan , mirip dengan assembler Intel x86 tradisional. Langkah pertama dalam mengurai assembler tinyvm adalah menjalankan preprocessor yang menafsirkan pernyataan %include filenamedan pernyataan %define identifier value.

Manipulasi teks semacam ini jauh lebih mudah dengan tipe &strdi Rust, jadi mari kita lihat antarmuka yang harus diterapkan oleh peti kita.

// vendor/tinyvm/include/tvm/tvm_preprocessor.h

#ifndef TVM_PREPROCESSOR_H_
#define TVM_PREPROCESSOR_H_

#include "tvm_htab.h"

int tvm_preprocess(char **src, int *src_len, struct tvm_htab_ctx *defines);

#endif

Menggunakan char **keduanya int *untuk variabel srcdan src_lenmungkin tampak sedikit aneh pada awalnya, tetapi jika Anda menulis padanannya di Rust, Anda akan mendapatkan hasil seperti ini:

fn tvm_preprocess(
    src: String,
    defines: &mut HashTable,
) -> Result<String, PreprocessorError> {
    ...
}

Kode C hanya menggunakan parameter keluaran untuk menggantikan string srcpada tempatnya, karena ia tidak dapat mengembalikan baik baris baru atau kode kesalahan.

Sebelum melakukan hal lain, Anda perlu menulis tes untuk tvm_preprocess(). Dengan cara ini kami dapat memastikan bahwa fungsi Rust secara fungsional setara dengan aslinya.

Kami berinteraksi dengan sistem file, jadi kami perlu mengeluarkan peti tempfile .

$ cargo add --dev tempfile
    Updating 'https://github.com/rust-lang/crates.io-index' index
      Adding tempfile v3.1.0 to dev-dependencies

Kami juga akan membutuhkan peti libckarena kami akan melewati garis libtvmyang mungkin perlu dibebaskan.

cargo add libc
    Updating 'https://github.com/rust-lang/crates.io-index' index
      Adding libc v0.2.66 to dev-dependencies

Melihat kode sumber, kita dapat melihat bahwa fungsi tvm_preprocess()akan terus mengizinkan %includedan %defineselama tidak.

Pertama, mari buat tes untuk memastikan preprocessor menangani %define. Kami tahu kode ini sudah berfungsi (ini adalah kode dari semua tinyvm), jadi seharusnya tidak ada kejutan.

// src/preprocessing.rs

#[cfg(test)]
mod tests {
    use crate::ffi;
    use std::{
        ffi::{CStr, CString},
        io::Write,
        os::raw::c_int,
    };

    #[test]
    fn find_all_defines() {
        let src = "%define true 1\nsome random text\n%define FOO_BAR -42\n";
        let original_length = src.len();
        let src = CString::new(src).unwrap();

        unsafe {
            // get a copy of `src` that was allocated using C's malloc
            let mut src = libc::strdup(src.as_ptr());
            let mut len = original_length as c_int;
            let defines = ffi::tvm_htab_create();

            let ret = ffi::tvm_preprocess(&mut src, &mut len, defines);

            // preprocessing should have been successful
            assert_eq!(ret, 0);

            // make sure the define lines were removed
            let preprocessed = CStr::from_ptr(src).to_bytes();
            let preprocessed =
                std::str::from_utf8(&preprocessed[..len as usize]).unwrap();
            assert_eq!(preprocessed, "\nsome random text\n\n");

            // make sure the "true" and "FOO_BAR" defines were set
            let true_define =
                ffi::tvm_htab_find_ref(defines, b"true\0".as_ptr().cast());
            let got = CStr::from_ptr(true_define).to_str().unwrap();
            assert_eq!(got, "1");
            let foo_bar =
                ffi::tvm_htab_find_ref(defines, b"FOO_BAR\0".as_ptr().cast());
            let got = CStr::from_ptr(foo_bar).to_str().unwrap();
            assert_eq!(got, "-42");

            // clean up our hashtable and copied source text
            ffi::tvm_htab_destroy(defines);
            libc::free(src.cast());
        }
    }
}

45 baris jauh lebih banyak daripada yang biasanya saya suka dalam pengujian, tetapi dibutuhkan cukup banyak kode tambahan untuk mengonversi bolak-balik antara baris C.

Kami juga perlu memeriksa, termasuk satu file lagi.

// src/preprocessing.rs

#[cfg(test)]
mod tests {
    ...

    #[test]
    fn include_another_file() {
        const TOP_LEVEL: &str = "first line\n%include nested\nlast line\n";
        const NESTED: &str = "nested\n";

        // the preprocessor imports files from the filesystem, so we need to
        // copy NESTED to a temporary location
        let mut nested = NamedTempFile::new().unwrap();
        nested.write_all(NESTED.as_bytes()).unwrap();
        let nested_filename = nested.path().display().to_string();

        // substitute the full path to the "nested" file
        let top_level_src = TOP_LEVEL.replace("nested", &nested_filename);
        std::fs::write(&nested, NESTED).unwrap();

        unsafe {
            let top_level_src = CString::new(top_level_src).unwrap();
            // create a copy of the top_level_src which can be freed by C
            let mut src = libc::strdup(top_level_src.as_ptr());
            let mut len = libc::strlen(src) as c_int;
            let defines = ffi::tvm_htab_create();

            // after all that setup code we can *finally* call the preprocessor
            let ret = ffi::tvm_preprocess(&mut src, &mut len, defines);

            assert_eq!(ret, 0);

            // make sure the define and import lines were removed
            let preprocessed = CStr::from_ptr(src).to_bytes();
            let got =
                std::str::from_utf8(&preprocessed[..len as usize]).unwrap();

            // after preprocessing, all include and define lines should have
            // been removed
            assert_eq!(got, "first line\nnested\nlast line\n");

            ffi::tvm_htab_destroy(defines);
            libc::free(src.cast());
        }
    }

Catatan

Sebagai catatan tambahan, pengujian ini awalnya ditulis untuk menumpuk semuanya dalam tiga lapisan dalam (misalnya, top_level.vmtermasuk nested.vm, yang menyertakan really_nested.vm) untuk memastikannya menangani lebih dari satu level %include, tetapi terlepas dari Seperti yang tertulis, tes terus segfault.

Kemudian saya mencoba menjalankan biner C asli tvmi...
$ cd vendor/tinyvm/
$ cat top_level.vm
  %include nested
$ cat nested.vm
  %include really_nested
$ cat really_nested.vm
  Hello World
$ ./bin/tvmi top_level.vm
  [1]    10607 segmentation fault (core dumped)  ./bin/tvmi top_level.vm
Ternyata tinyvm asli crash karena beberapa alasan ketika Anda memiliki banyak lapisan include...

Jadi sekarang kami memiliki beberapa pengujian, jadi kami dapat mulai menerapkan tvm_preprocess().

Pertama, Anda perlu menentukan jenis kesalahannya.

// src/preprocessing.rs

#[derive(Debug)]
pub enum PreprocessingError {
    FailedInclude {
        name: String,
        inner: IoError,
    },
    DuplicateDefine {
        name: String,
        original_value: String,
        new_value: String,
    },
    EmptyDefine,
    DefineWithoutValue(String),
}

Melihat fungsi process_includes () dan process_derives () , tampaknya mereka memindai string mencari direktif tertentu, dan kemudian mengganti string itu dengan sesuatu yang lain (baik konten file, atau tidak sama sekali jika baris harus dihapus).

Kita harus bisa mengekstrak logika ini menjadi helper dan menghindari duplikasi yang tidak perlu.

// src/preprocessing.rs

/// Scan through the input string looking for a line starting with some
/// directive, using a callback to figure out what to replace the directive line
/// with.
fn process_line_starting_with_directive<F>(
    mut src: String,
    directive: &str,
    mut replace_line: F,
) -> Result<(String, usize), PreprocessingError>
where
    F: FnMut(&str) -> Result<String, PreprocessingError>,
{
    // try to find the first instance of the directive
    let directive_delimiter = match src.find(directive) {
        Some(ix) => ix,
        None => return Ok((src, 0)),
    };

    // calculate the span from the directive to the end of the line
    let end_ix = src[directive_delimiter..]
        .find('\n')
        .map(|ix| ix + directive_delimiter)
        .unwrap_or(src.len());

    // the rest of the line after the directive
    let directive_line =
        src[directive_delimiter + directive.len()..end_ix].trim();

    // use the callback to figure out what we should replace the line with
    let replacement = replace_line(directive_line)?;

    // remove the original line
    let _ = src.drain(directive_delimiter..end_ix);
    // then insert our replacement
    src.insert_str(directive_delimiter, &replacement);

    Ok((src, 1))
}

Kami sekarang memiliki helper process_line_starting_with_directive(), jadi kami dapat menerapkan parser %include.

// src/preprocessing.rs

fn process_includes(
    src: String,
) -> Result<(String, usize), PreprocessingError> {
    const TOK_INCLUDE: &str = "%include";

    process_line_starting_with_directive(src, TOK_INCLUDE, |line| {
        std::fs::read_to_string(line).map_err(|e| {
            PreprocessingError::FailedInclude {
                name: line.to_string(),
                inner: e,
            }
        })
    })
}

Sayangnya, parser% define sedikit lebih rumit.

// src/preprocessing.rs

n process_defines(
    src: String,
    defines: &mut HashTable,
) -> Result<(String, usize), PreprocessingError> {
    const TOK_DEFINE: &str = "%define";

    process_line_starting_with_directive(src, TOK_DEFINE, |line| {
        parse_define(line, defines)?;
        Ok(String::new())
    })
}

fn parse_define(
    line: &str,
    defines: &mut HashTable,
) -> Result<(), PreprocessingError> {
    if line.is_empty() {
        return Err(PreprocessingError::EmptyDefine);
    }

    // The syntax is "%define key value", so after removing the leading
    // "%define" everything after the next space is the value
    let first_space = line.find(' ').ok_or_else(|| {
        PreprocessingError::DefineWithoutValue(line.to_string())
    })?;

    // split the rest of the line into key and value
    let (key, value) = line.split_at(first_space);
    let value = value.trim();

    match defines.0.entry(
        CString::new(key).expect("The text shouldn't contain null bytes"),
    ) {
        // the happy case, this symbol hasn't been defined before so we can just
        // insert it.
        Entry::Vacant(vacant) => {
            vacant.insert(Item::opaque(value));
        },
        // looks like this key has already been defined, report an error
        Entry::Occupied(occupied) => {
            return Err(PreprocessingError::DuplicateDefine {
                name: key.to_string(),
                original_value: occupied
                    .get()
                    .opaque_value_str()
                    .unwrap_or("<invalid>")
                    .to_string(),
                new_value: value.to_string(),
            });
        },
    }

    Ok(())
}

Untuk mengakses teks dalam tabel hash kita, kita perlu memberikan elemen tersebut Itembeberapa metode pembantu:

// src/htab.rs

impl Item {
    ...

    pub(crate) fn opaque_value(&self) -> &[u8] { &self.opaque_value }

    pub(crate) fn opaque_value_str(&self) -> Option<&str> {
        std::str::from_utf8(self.opaque_value()).ok()
    }
}

Ada baiknya menambahkan beberapa tes lagi pada saat ini.

// src/preprocessing.rs

#[cfg(test)]
mod tests {
    ...

    #[test]
    fn empty_string() {
        let src = String::from("");
        let mut hashtable = HashTable::default();

        let (got, replacements) = process_defines(src, &mut hashtable).unwrap();

        assert!(got.is_empty());
        assert_eq!(replacements, 0);
        assert!(hashtable.0.is_empty());
    }

    #[test]
    fn false_percent() {
        let src = String::from("this string contains a % symbol");
        let mut hashtable = HashTable::default();

        let (got, replacements) =
            process_defines(src.clone(), &mut hashtable).unwrap();

        assert_eq!(got, src);
        assert_eq!(replacements, 0);
        assert!(hashtable.0.is_empty());
    }

    #[test]
    fn define_without_key_and_value() {
        let src = String::from("%define\n");
        let mut hashtable = HashTable::default();

        let err = process_defines(src.clone(), &mut hashtable).unwrap_err();

        match err {
            PreprocessingError::EmptyDefine => {},
            other => panic!("Expected EmptyDefine, found {:?}", other),
        }
    }

    #[test]
    fn define_without_value() {
        let src = String::from("%define key\n");
        let mut hashtable = HashTable::default();

        let err = process_defines(src.clone(), &mut hashtable).unwrap_err();

        match err {
            PreprocessingError::DefineWithoutValue(key) => {
                assert_eq!(key, "key")
            },
            other => panic!("Expected DefineWithoutValue, found {:?}", other),
        }
    }

    #[test]
    fn valid_define() {
        let src = String::from("%define key value\n");
        let mut hashtable = HashTable::default();

        let (got, num_defines) = process_defines(src.clone(), &mut hashtable).unwrap();

        assert_eq!(got, "\n");
        assert_eq!(num_defines, 1);
        assert_eq!(hashtable.0.len(), 1);
        let key = CString::new("key").unwrap();
        let item = hashtable.0.get(&key).unwrap();
        assert_eq!(item.opaque_value_str().unwrap(), "value");
    }
}

Pada titik ini, kami telah mereproduksi sebagian besar logika preprocessing, jadi sekarang kami hanya memerlukan fungsi yang akan terus memperluas operator %includedan proses %definehingga tidak ada lagi.

// src/preprocessing.rs

pub fn preprocess(
    src: String,
    defines: &mut HashTable,
) -> Result<String, PreprocessingError> {
    let mut src = src;

    loop {
        let (modified, num_includes) = process_includes(src)?;
        let (modified, num_defines) = process_defines(modified, defines)?;

        if num_includes + num_defines == 0 {
            return Ok(modified);
        }

        src = modified;
    }
}

Tentu saja, fitur preprocess()ini hanya tersedia untuk Rust. Kita perlu membuatnya extern "C" fnyang menerjemahkan argumen dari tipe C menjadi sesuatu yang bisa ditangani Rust, dan kemudian diterjemahkan kembali ke C.

// src/preprocessing.rs

#[no_mangle]
pub unsafe extern "C" fn tvm_preprocess(
    src: *mut *mut c_char,
    src_len: *mut c_int,
    defines: *mut tvm_htab_ctx,
) -> c_int {
    if src.is_null() || src_len.is_null() || defines.is_null() {
        return -1;
    }

    // Safety: This assumes the tvm_htab_ctx is actually our ported HashTable
    let defines = &mut *(defines as *mut HashTable);

    // convert the input string to an owned Rust string so it can be
    // preprocessed
    let rust_src = match CStr::from_ptr(*src).to_str() {
        Ok(s) => s.to_string(),
        // just error out if it's not valid UTF-8
        Err(_) => return -1,
    };

    match preprocess(rust_src, defines) {
        Ok(s) => {
            let preprocessed = CString::new(s).unwrap();
            // create a copy of the preprocessed string that can be free'd by C
            // and use the output arguments to pass it to the caller
            *src = libc::strdup(preprocessed.as_ptr());
            // the original C implementation didn't add a null terminator to the
            // preprocessed string, so we're required to set the length as well.
            *src_len = libc::strlen(*src) as c_int;

            // returning 0 indicates success
            0
        },
        // tell the caller "an error occurred"
        Err(_) => -1,
    }
}

Tip Anda

mungkin telah memperhatikan bahwa fungsi tvm_preprocess () kami tidak memiliki logika preprocessing dan lebih seperti adaptor untuk menerjemahkan argumen dan mengembalikan nilai dan memastikan penyebaran kesalahan yang benar.

Ini bukan kebetulan.

Rahasia coding FFI adalah menulis sesedikit mungkin dan menghindari trik cerdas . Tidak seperti kebanyakan kode Rust, bug dalam fungsi interop semacam itu dapat menyebabkan bug dalam logika dan memori.

Membuat pembungkus tipis di sekitar fungsi kita preprocess()juga membuat segalanya lebih mudah: ketika sebagian besar basis kode ditulis dalam Rust, kita dapat menghapus pembungkusnya dan memanggil preprocess()secara langsung.

Fungsi tersebut sekarang telah tvm_preprocess()ditentukan dan kita harus siap untuk pergi.

 Compiling tinyvm v0.1.0 (/home/michael/Documents/tinyvm-rs)
error: linking with `/usr/bin/clang` failed: exit code: 1
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  = note: "/usr/bin/clang" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.13h6j6k0dzqf6zi2.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.13l2b4uvr7p3ht4k.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.14bdbjhozo3id49g.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.14fw2gyd6mrq5730.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.19xc7n0bb25uaxgk.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.1duzy573vjvyihco.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.1e0yejy24qufh7ie.rcgu.o" 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"/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.njyqsm0frvb1j4d.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.r9ttxk3s5kacz9k.rcgu.o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.xrorvssabbgfjqz.rcgu.o" "-o" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88" "/home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.1iplfu0pt8fy07e4.rcgu.o" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs" "-L" "/home/michael/Documents/tinyvm-rs/target/debug/deps" "-L" "/home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out" "-L" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-Wl,--whole-archive" "-ltvm" "-Wl,--no-whole-archive" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libtest-a39a3e9a77b17f55.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libterm-97a69cd310ff0925.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgetopts-66a42b1d94e3e6f9.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunicode_width-dd7761d848144e0d.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_std-f722acdb78755ba0.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/libtempfile-b08849d192e5c2e1.rlib"
 "/home/michael/Documents/tinyvm-rs/target/debug/deps/librand-c85ceffb304c7385.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/librand_chacha-4e4839e3036afe89.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/libc2_chacha-7555b62a53de8bdf.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/libppv_lite86-0097c0f425957d6e.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/librand_core-de2208c863d15e9b.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/libgetrandom-c696cd809d660e17.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/liblibc-d52d0b97a33a5f02.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/libremove_dir_all-4035fb46dbd6fb92.rlib" "/home/michael/Documents/tinyvm-rs/target/debug/deps/libcfg_if-6adeb646d05b676c.rlib" "-Wl,--start-group" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-974c3c08f6def4b3.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-eb49676f33a2c8a6.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-7ae0446feecc60f2.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-2de299b65d7f5721.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libbacktrace-64514775bc06309a.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libbacktrace_sys-1ed8aa185c63b9a5.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-a839df87f563fba5.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-8e726bdc2018d836.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-5285f42cbadf207d.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-b0362d20f8aa58fa.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-f3dd7051708453a4.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-83744846c43307ce.rlib" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-d5565a3a0f4cfe21.rlib" "-Wl,--end-group" "/home/michael/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-ea790e85415e3bbf.rlib" "-Wl,-Bdynamic" "-lutil" "-lutil" "-ldl" "-lrt" "-lpthread" "-lgcc_s" "-lc" "-lm" "-lrt" "-lpthread" "-lutil" "-lutil" "-fuse-ld=lld"
  = note: ld.lld: error: duplicate symbol: tvm_preprocess
          >>> defined at preprocessing.rs:13 (src/preprocessing.rs:13)
          >>>            /home/michael/Documents/tinyvm-rs/target/debug/deps/tinyvm-8eca24ff9a1cde88.4mgvbbhn4jewmy60.rcgu.o:(tvm_preprocess)
          >>> defined at tvm_preprocessor.c:135 (vendor/tinyvm/libtvm/tvm_preprocessor.c:135)
          >>>            tvm_preprocessor.o:(.text.tvm_preprocess+0x0) in archive /home/michael/Documents/tinyvm-rs/target/debug/build/tinyvm-3f1a2766f78b5580/out/libtvm.a
          clang: error: linker command failed with exit code 1 (use -v to see invocation)


error: aborting due to previous error

error: could not compile `tinyvm`.

To learn more, run the command again with --verbose.

Ups, linker mengeluh dan preprocessing.rs, dan tvm_preprocessor.cmenetapkan fungsi tvm_preprocess(). Sepertinya kami lupa menghapus tvm_preprocessor.cdari perakitan ...

diff --git a/build.rs b/build.rs
index 0ed012c..42b8fa0 100644
--- a/build.rs
+++ b/build.rs
@@ -14,6 +14,7 @@ fn main() {
         .file(src.join("tvm_memory.c"))
         .file(src.join("tvm_parser.c"))
         .file(src.join("tvm_program.c"))
-        .file(src.join("tvm_preprocessor.c"))
         .file(src.join("tvm.c"))
         .include(&include)
         .compile("tvm");
(END)

Mari kita coba lagi.

cargo run --example tvmi -- vendor/tinyvm/programs/tinyvm/fact.vm
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/examples/tvmi vendor/tinyvm/programs/tinyvm/fact.vm`
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Jauh lebih baik!

Ingat contoh terakhir, di mana Anda tvmijatuh, mendapatkan tiga tingkat kedalaman kode? Sebagai efek samping yang bagus, setelah mem-porting kode Anda ke Rust, lapisan bersarang hanya berfungsi .

Catatan Anda

mungkin juga memperhatikan bahwa fungsi preprocess()tersebut tidak menggunakan salah satu fungsi tabel hash dari tvm_htab.h. Setelah mem-port modul ke Rust, kami hanya menggunakan tipe Rust secara langsung.

Inilah keindahan dari proses ini. Setelah Anda mentransfer sesuatu ke Rust, Anda dapat menerapkannya untuk menggunakan jenis / fungsi secara langsung - dan langsung mendapatkan keuntungan dari penanganan kesalahan dan ergonomi.

Kesimpulan

Jika Anda masih membaca artikel ini, selamat, kami baru saja memindahkan dua modul dari tinyvmke Rust.

Sayangnya artikel ini sudah cukup panjang. Tapi saya harap sekarang Anda sudah mendapatkan gambaran besarnya.

Jelajahi header aplikasi dan temukan fungsi / modul sederhana
Tulis beberapa pengujian untuk memahami bagaimana fungsi yang ada harus bekerja
Tulis fungsi yang setara di Rust dan pastikan mereka lulus tes yang sama
Buat shim tipis yang mengekspor fungsi Rust dengan antarmuka C yang sama, ingat untuk menghapus fungsi / modul asli dari rakitan sehingga linker menggunakan kode Rust sebagai ganti C
Lanjutkan ke langkah 1

Hal terbaik tentang metode ini adalah Anda secara bertahap meningkatkan basis kode, aplikasi tetap berfungsi, dan Anda tidak menulis ulang semuanya dari awal hingga akhir.

Ini seperti mengganti roda dengan cepat.

Cara yang disukai untuk mem-port aplikasi dari C ke Rust

Lihat juga:

" Lima Tahun Karat "

" C ++ lebih cepat dan lebih aman daripada Rust, Yandex melakukan pengukuran "

« Rust untuk pengembang Java "

Cara menulis ulang kode di Rust

Mulai

Buah gantung rendah

Implementasi preprocessing data

Kesimpulan

More articles: