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分享使用 Rust 进行嵌入式开发
Rust 是一门赋予每个人 构建可靠且高效软件能力的语言。
本文由RT-Thread论坛用户@Papalymo原创发布：https://club.rt-thread.org/ask/article/2944.html
#使用 Rust 进行嵌入式开发
##Rust 是什么
Rust 是一门赋予每个人 构建可靠且高效软件能力的语言。
- 高性能：速度惊人且内存利用率极高
- 可靠性：在编译期就能消除各种内存错误
- 生产力：出色的文档，友好的编译器和清晰的错误提示信息
## 为什么要用 Rust 进行嵌入式开发
Rust 的设计理念：既要安全，也要高性能。Rust 的设计理念完全是嵌入式开发所需要的。
嵌入式软件在运行过程中出现问题，大部分是由于内存引起的。Rust 语言可以说是一门面向编译器的语言。在编译期间，就能够确保你安全地使用内存。
目前，嵌入式的主流开发语言还是 C 语言，不能上来就把底层的逻辑用 Rust 重新实现一遍。但是可以在 C 代码中嵌入 Rust 语言。
##C 调用 Rust
在 C 代码中调用 Rust 代码，需要我们将 Rust 源代码打包为静态库文件。在 C 代码编译时，链接进去。
###创建 lib 库
1. 在 Clion 中使用 `cargo init --lib rust_to_c` 建立 lib 库。添加以下代码到 lib.rs 中，使用 Rust 语言计算两个整数的和：
rust
#![no_std]
use core::panic::PanicInfo;
#[no_mangle]
pub extern "C" fn sum(a: i32, b: i32) -> i32 {
a + b
}
#[panic_handler]
fn panic(_info:&PanicInfo) -> !{
loop{}
}
```
2. 在 Cargo.toml 文件中添加以下代码，生成静态库文件：
```
[lib]
name = "sum"
crate-type = ["staticlib"]
path = "src/lib.rs"
###交叉编译
1. 安装 armv7 target:
rustup target add armv7a-none-eabi
2. 生成静态库文件：
rust
PS C:\Users\LiuKang\Desktop\RUST\rust_to_c> cargo build --target=armv7a-none-eabi --release --verbose
Fresh rust_to_c v0.1.0 (C:\Users\LiuKang\Desktop\RUST\rust_to_c)
Finished release [optimized] target(s) in 0.01s
###生成头文件
1. 安装 [cbindgen]([eqrion/cbindgen: A project for generating C bindings from Rust code (github.com)](https://github.com/eqrion/cbindgen)), cbindgen 从 rust 库生成 C/C++ 11 头文件：
cargo install --force cbindgen
2. 在项目文件夹下新建文件 `cbindgen.toml` 文件：
3. 生成头文件：
cbindgen --config cbindgen.toml --crate rust_to_c --output sum.h
###调用 Rust 库文件
1. 将生成的`sum.h` 以及 `sum.a` 文件放入 `rt-thread\bsp\qemu-vexpress-a9\applications` 目录下
2. 修改 SConscript 文件，添加静态库:
rust
from building import *
cwd = GetCurrentDir()
src = Glob('*.c') + Glob('*.cpp')
CPPPATH = [cwd]
LIBS = ["libsum.a"]
LIBPATH = [GetCurrentDir()]
group = DefineGroup('Applications', src, depend = [''], CPPPATH = CPPPATH, LIBS = LIBS, LIBPATH = LIBPATH)
Return('group')
3. 在 main 函数中调用 sum 函数, 并获取返回值
rust
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <rtthread.h>
#include "sum.h"
int main(void)
{
int32_t tmp;
tmp = sum(1, 2);
printf("call rust sum(1, 2) = %d\n", tmp);
return 0;
}
4. 在 env 环境下，使用 scons 编译工程：
`rust
LiuKang@DESKTOP-538H6DE D:\repo\github\rt-thread\bsp\qemu-vexpress-a9
$ scons -j6
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: warning: you do not seem to have the pywin32 extensions installed;
parallel (-j) builds may not work reliably with open Python files.
File "D:\software\env_released_1.2.0\env\tools\Python27\Scripts\scons.py", line 204, in <module>
scons: Building targets ...
scons: building associated VariantDir targets: build
LINK rtthread.elf
arm-none-eabi-objcopy -O binary rtthread.elf rtthread.bin
arm-none-eabi-size rtthread.elf
text data bss dec hex filename
628220 2148 86700 717068 af10c rtthread.elf
scons: done building targets.
LiuKang@DESKTOP-538H6DE D:\repo\github\rt-thread\bsp\qemu-vexpress-a9
$ qemu.bat
WARNING: Image format was not specified for 'sd.bin' and probing guessed raw.
Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
Specify the 'raw' format explicitly to remove the restrictions.
\ | /
- RT - Thread Operating System
/ | \ 4.0.4 build Jul 28 2021
2006 - 2021 Copyright by rt-thread team
lwIP-2.1.2 initialized!
[I/sal.skt] Socket Abstraction Layer initialize success.
[I/SDIO] SD card capacity 65536 KB.
[I/SDIO] switching card to high speed failed!
call rust sum(1, 2) = 3
msh />
###加减乘除
1. 在 lib.rs 文件中，使用 rust 语言实现加减乘除运算：
rust
#![no_std]
use core::panic::PanicInfo;
#[no_mangle]
pub extern "C" fn add(a: i32, b: i32) -> i32 {
a + b
}
#[no_mangle]
pub extern "C" fn subtract(a: i32, b: i32) -> i32 {
a - b
}
#[no_mangle]
pub extern "C" fn multiply(a: i32, b: i32) -> i32 {
a * b
}
#[no_mangle]
pub extern "C" fn divide(a: i32, b: i32) -> i32 {
a / b
}
#[panic_handler]
fn panic(_info:&PanicInfo) -> !{
loop{}
}
2. 生成库文件和头文件并放在 application 目录下
3. 使用 scons 编译，链接时报错，在 rust github 仓库的 issues 中找到了 [解决办法](https://github.com/rust-lang/compiler-builtins/issues/353) ：
rust
LINK rtthread.elf
d:/software/env_released_1.2.0/env/tools/gnu_gcc/arm_gcc/mingw/bin/../lib/gcc/arm-none-eabi/5.4.1/armv7-ar/thumb\libgcc.a(_arm_addsubdf3.o): In function `__aeabi_ul2d':
(.text+0x304): multiple definition of `__aeabi_ul2d'
applications\libsum.a(compiler_builtins-9b744f6fddf5e719.compiler_builtins.20m0qzjq-cgu.117.rcgu.o):/cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.35/src/float/conv.rs:143: first defined here
collect2.exe: error: ld returned 1 exit status
scons: *** [rtthread.elf] Error 1
scons: building terminated because of errors.
```
4. 修改 `rtconfig.py` 文件， 添加链接参数 `--allow-multiple-definition`：
```rust
DEVICE = ' -march=armv7-a -marm -msoft-float'
CFLAGS = DEVICE + ' -Wall'
AFLAGS = ' -c' + DEVICE + ' -x assembler-with-cpp -D__ASSEMBLY__ -I.'
LINK_SCRIPT = 'link.lds'
LFLAGS = DEVICE + ' -nostartfiles -Wl,--gc-sections,-Map=rtthread.map,-cref,-u,system_vectors,--allow-multiple-definition'+\
' -T %s' % LINK_SCRIPT
CPATH = ''
LPATH = ''
5. 编译并运行 qemu：
LiuKang@DESKTOP-538H6DE D:\repo\github\rt-thread\bsp\qemu-vexpress-a9
$ scons -j6
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: warning: you do not seem to have the pywin32 extensions installed;
parallel (-j) builds may not work reliably with open Python files.
File "D:\software\env_released_1.2.0\env\tools\Python27\Scripts\scons.py", line 204, in <module>
scons: Building targets ...
scons: building associated VariantDir targets: build
LINK rtthread.elf
arm-none-eabi-objcopy -O binary rtthread.elf rtthread.bin
arm-none-eabi-size rtthread.elf
text data bss dec hex filename
628756 2148 86700 717604 af324 rtthread.elf
scons: done building targets.
LiuKang@DESKTOP-538H6DE D:\repo\github\rt-thread\bsp\qemu-vexpress-a9
$ qemu.bat
WARNING: Image format was not specified for 'sd.bin' and probing guessed raw.
Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
Specify the 'raw' format explicitly to remove the restrictions.
\ | /
- RT - Thread Operating System
/ | \ 4.0.4 build Jul 28 2021
2006 - 2021 Copyright by rt-thread team
lwIP-2.1.2 initialized!
[I/sal.skt] Socket Abstraction Layer initialize success.
[I/SDIO] SD card capacity 65536 KB.
[I/SDIO] switching card to high speed failed!
call rust sum(1, 2) = 3
call rust subtract(2, 1) = 1
call rust multiply(2, 2) = 4
call rust divide(4, 2) = 2
更多内容欢迎查看原文：
https://club.rt-thread.org/ask/article/2944.html
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杨东杰 2021-11-11
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Rust和Go的应用越来越广泛了
