构建依赖libcuda多依赖项的Rust crate时解决链接错误

我有一个名为foo的Rust crate，依赖两个库：

• cudarc：对应CUDA驱动API的libcuda的sys crate
• rs-smctrl：我为调用libcuda的C库libsmctrl编写的sys crate

单独构建cudarc或rs-smctrl都能成功，foo只依赖其中一个时也可正常编译，但同时引入两个依赖就会触发链接器错误。我的目标是让foo静态链接libsmctrl，动态链接libcuda。

链接错误详情 #

...
  = note: /usr/bin/ld: /h/bez/work/rs-smctrl/target/debug/deps/librs_smctrl-ee6526e2da5cab52.rlib(libsmctrl.o): in function `setup_g_sm_control_10':
          /h/bez/work/rs-smctrl/src/libsmctrl.c:53: undefined reference to `cudbgReportDriverApiErrorFlags'
          clang: error: linker command failed with exit code 1 (use -v to see invocation)
          
  = note: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

error: could not compile `rs-smctrl` (bin "rs-smctrl") due to previous error

rs-smctrl的build.rs代码 #

# `build.rs` for `rs-smctrl`
fn main() {
    println!("cargo:rustc-link-lib=dylib=cuda");

    let src = ["src/libsmctrl.c"];
    let mut builder = cc::Build::new();
    let build = builder
        .files(src.iter())
        .include("/usr/local/cuda/include")
        .flag("-Wno-unused-parameter")
        .flag("-Wno-parentheses")
        .flag("-Wno-sign-compare");
    build.compile("libsmctrl");
}

foo的配置（注释cudarc即可正常构建） #

Cargo.toml #

# `Cargo.toml` for `foo`:
[package]
name = "foo"
version = "0.1.0"
edition = "2021"

[dependencies]
cudarc = { version="0.9.15", features=["std", "driver"], default-features = false }
rs-smctrl = { git = "https://github.com/atomicapple0/rs-smctrl.git" }

main.rs #

# `main.rs` for `foo`
fn main() {
    unsafe { rs_smctrl::libsmctrl_set_global_mask(0) };
    println!("Hello, world!");
}

这个问题本质是链接顺序冲突：同时引入两个依赖时，Cargo自动排序的链接顺序可能导致libcuda的符号在rs-smctrl之后被处理，导致rs-smctrl找不到cudbgReportDriverApiErrorFlags这类符号。以下是几个实用解法：

方法1：强制调整libcuda的链接顺序 #

修改rs-smctrl的build.rs，把原来的cargo:rustc-link-lib=dylib=cuda换成直接指定链接参数，强制让libcuda排在前面：

fn main() {
    // 用link-arg强制指定链接顺序，确保libcuda先被处理
    println!("cargo:rustc-link-arg=-lcuda");

    let src = ["src/libsmctrl.c"];
    let mut builder = cc::Build::new();
    let build = builder
        .files(src.iter())
        .include("/usr/local/cuda/include")
        .flag("-Wno-unused-parameter")
        .flag("-Wno-parentheses")
        .flag("-Wno-sign-compare");
    build.compile("libsmctrl");
}

方法2：全局声明libcuda链接 #

在foo的根目录新建build.rs，添加全局的libcuda链接指令，确保所有依赖都能找到完整的符号：

// foo的build.rs
fn main() {
    println!("cargo:rustc-link-lib=dylib=cuda");
}

方法3：让rs-smctrl依赖cudarc调整链接顺序 #

在rs-smctrl的Cargo.toml中添加cudarc作为构建依赖，让Cargo自动调整链接顺序：

[build-dependencies]
cudarc = { version="0.9.15", features=["driver"], default-features = false }

同时保留原build.rs中的cargo:rustc-link-lib=dylib=cuda即可。

内容的提问来源于stack exchange，提问作者atomicapple0