文件列表見：Rust 移動端跨平臺複雜圖形渲染專案開發系列總結（目錄）

專案編譯前的操作 build.rs

build.rs可實現正常專案編譯前的額外操作，比如程式碼生成、編譯所依賴的C/C++庫等行為。為了讓程式設計過程更可控，通常需要輸出狀態表示通過了某一階段，或遇到什麼錯誤，Cargo支援build.rs編譯時輸出不同型別的語句，比如info、warning、error等，以下為示例，參考自rustdroid-native。

println!("cargo:warning=Error executing process command <{:?}>: {}", cmd, e);
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呼叫C/C++編譯器編譯所依賴的第三方C/C++庫

目前我看到比較完整的參考是官方的libstd/build.rs，編譯我們業務所需的第三方庫的命令幾乎都可以從那找到“靈感”，下面貼出完整程式碼鎮宅，關鍵操作是build_libbacktrace()，通過cc::Build例項把需要編譯的C/C++程式碼宣告起來，理論上支援正則匹配檔名與路徑 。

#![deny(warnings)]

extern crate build_helper;
extern crate cc;

use build_helper::native_lib_boilerplate;
use std::env;
use std::fs::File;

fn
 
 main() {
    let target = env::var("TARGET").expect("TARGET was not set");
    if cfg!(feature = "backtrace") &&
        !target.contains("cloudabi") &&
        !target.contains("emscripten") &&
        !target.contains("msvc") &&
        !target.contains("wasm32")
    {
        let
 
 _ = build_libbacktrace(&target);
    }

    if target.contains("linux") {
        if target.contains("android") {
            println!("cargo:rustc-link-lib=dl");
            println!("cargo:rustc-link-lib=log");
            println!("cargo:rustc-link-lib=gcc");
        } else if !target.contains("musl") {
            println!("cargo:rustc-link-lib=dl");
            println!("cargo:rustc-link-lib=rt");
            println!("cargo:rustc-link-lib=pthread");
        }
    } else if target.contains("freebsd") {
        println!("cargo:rustc-link-lib=execinfo");
        println!("cargo:rustc-link-lib=pthread");
    } else if target.contains("dragonfly") || target.contains("bitrig") ||
              target.contains("netbsd") || target.contains("openbsd") {
        println!("cargo:rustc-link-lib=pthread");
    } else if target.contains("solaris") {
        println!("cargo:rustc-link-lib=socket");
        println!("cargo:rustc-link-lib=posix4");
        println!("cargo:rustc-link-lib=pthread");
        println!("cargo:rustc-link-lib=resolv");
    } else if target.contains("apple-darwin") {
        println!("cargo:rustc-link-lib=System");

        // res_init and friends require -lresolv on macOS/iOS.
        // See #41582 and http://blog.achernya.com/2013/03/os-x-has-silly-libsystem.html
        println!("cargo:rustc-link-lib=resolv");
    } else if target.contains("apple-ios") {
        println!("cargo:rustc-link-lib=System");
        println!("cargo:rustc-link-lib=objc");
        println!("cargo:rustc-link-lib=framework=Security");
        println!("cargo:rustc-link-lib=framework=Foundation");
        println!("cargo:rustc-link-lib=resolv");
    } else if target.contains("windows") {
        println!("cargo:rustc-link-lib=advapi32");
        println!("cargo:rustc-link-lib=ws2_32");
        println!("cargo:rustc-link-lib=userenv");
        println!("cargo:rustc-link-lib=shell32");
    } else if target.contains("fuchsia") {
        println!("cargo:rustc-link-lib=zircon");
        println!("cargo:rustc-link-lib=fdio");
    } else if target.contains("cloudabi") {
        if cfg!(feature = "backtrace") {
            println!("cargo:rustc-link-lib=unwind");
        }
        println!("cargo:rustc-link-lib=c");
        println!("cargo:rustc-link-lib=compiler_rt");
    }
}

fn build_libbacktrace(target: &str) -> Result<(), ()> {
    let native = native_lib_boilerplate("libbacktrace", "libbacktrace", "backtrace", "")?;

    let mut build = cc::Build::new();
    build
        .flag("-fvisibility=hidden")
        .include("../libbacktrace")
        .include(&native.out_dir)
        .out_dir(&native.out_dir)
        .warnings(false)
        .file("../libbacktrace/alloc.c")
        .file("../libbacktrace/backtrace.c")
        .file("../libbacktrace/dwarf.c")
        .file("../libbacktrace/fileline.c")
        .file("../libbacktrace/posix.c")
        .file("../libbacktrace/read.c")
        .file("../libbacktrace/sort.c")
        .file("../libbacktrace/state.c");

    let any_debug = env::var("RUSTC_DEBUGINFO").unwrap_or_default() == "true" ||
        env::var("RUSTC_DEBUGINFO_LINES").unwrap_or_default() == "true";
    build.debug(any_debug);

    if target.contains("darwin") {
        build.file("../libbacktrace/macho.c");
    } else if target.contains("windows") {
        build.file("../libbacktrace/pecoff.c");
    } else {
        build.file("../libbacktrace/elf.c");

        let pointer_width = env::var("CARGO_CFG_TARGET_POINTER_WIDTH").unwrap();
        if pointer_width == "64" {
            build.define("BACKTRACE_ELF_SIZE", "64");
        } else {
            build.define("BACKTRACE_ELF_SIZE", "32");
        }
    }

    File::create(native.out_dir.join("backtrace-supported.h")).unwrap();
    build.define("BACKTRACE_SUPPORTED", "1");
    build.define("BACKTRACE_USES_MALLOC", "1");
    build.define("BACKTRACE_SUPPORTS_THREADS", "0");
    build.define("BACKTRACE_SUPPORTS_DATA", "0");

    File::create(native.out_dir.join("config.h")).unwrap();
    if !target.contains("apple-ios") &&
       !target.contains("solaris") &&
       !target.contains("redox") &&
       !target.contains("android") &&
       !target.contains("haiku") {
        build.define("HAVE_DL_ITERATE_PHDR", "1");
    }
    build.define("_GNU_SOURCE", "1");
    build.define("_LARGE_FILES", "1");

    build.compile("backtrace");
    Ok(())
}
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條件編譯

所有的條件編譯都由通過cfg配置實現，cfg支援any、all、not等邏輯謂詞組合。

基本用法

在Cargo.toml中新增[features]段，然後列舉需要組合的feature名，大體上相當於gcc -條件1 -條件2 -條件3 ...。

[features]
default = []
metal = ["gfx-backend-metal"]
vulkan = ["gfx-backend-vulkan"]
dx12 = ["gfx-backend-dx12"]
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mod級別條件編譯

實現示例，參考gl_generator.rs

#[cfg(feature = "unstable_generator_utils")]
pub mod generators;
#[cfg(not(feature = "unstable_generator_utils"))]
mod generators;
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編譯特定CPU架構

指定target_arch + CPU架構名稱字串，如#[cfg(target_arch= "x86")]，#[cfg(any(target_arch = "arm", target_arch = "x86"))]。

參考libstd/os/android/raw.rs

#[cfg(any(target_arch = "arm", target_arch = "x86"))]
mod arch {
    use os::raw::{c_uint, c_uchar, c_ulonglong, c_longlong, c_ulong};
    use os::unix::raw::{uid_t, gid_t};

    #[stable(feature = "raw_ext", since = "1.1.0")]
    pub type dev_t = u64;
    #[stable(feature = "raw_ext", since = "1.1.0")]
    pub type mode_t = u32;

    #[stable(feature = "raw_ext", since = "1.1.0")]
    pub type blkcnt_t = u64;
    #[stable(feature = "raw_ext", since = "1.1.0")]
    pub type blksize_t = u64;
    #[stable(feature = "raw_ext", since = "1.1.0")]
    pub type ino_t = u64;
    #[stable(feature = "raw_ext", since = "1.1.0")]
    pub type nlink_t = u64;
    #[stable(feature = "raw_ext", since = "1.1.0")]
    pub type off_t = u64;
    #[stable(feature = "raw_ext", since = "1.1.0")]
    pub type time_t = i64;
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#[doc(include = "os/raw/char.md")]
#[cfg(any(all(target_os = "linux", any(target_arch = "aarch64",
                                       target_arch = "arm",
                                       target_arch = "powerpc",
                                       target_arch = "powerpc64",
                                       target_arch = "s390x")),
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[target.'cfg(any(target_os = "macos", all(target_os = "ios", target_arch = "aarch64")))'.dependencies.gfx-backend-metal]
git = "https://github.com/gfx-rs/gfx"
version = "0.1"
optional = true

[target.'cfg(target_os = "android")'.dependencies.gfx-backend-vulkan]
git = "https://github.com/gfx-rs/gfx"
version = "0.1"
optional = true

#[target.'cfg(windows)'.dependencies.gfx-backend-dx12]
#git = "https://github.com/gfx-rs/gfx"
#version = "0.1"
#optional = true
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編譯成指定型別二進位制包(.a/.so/.r)

目前還沒找到支援編譯出macOS/iOS支援的.framework辦法。

在Cargo.toml中新增[lib]段，

• name表示輸出的庫名，最終輸出檔名為lib+name.a或lib+name.so，比如libportability.so。
• crate-type表示輸出的二進位制包型別，比如
  • staticlib = .a iOS只認Rust輸出.a，Android可以.a和.so，配置成["staticlib", "cdylib"]在用cargo-lipo時會出警告不支援cdylib，忽略即可。
  • cdylib = .so
  • rlib = 給Rust用的靜態庫
  • dylib = 給Rust用的動態庫
• path表示庫專案的入口檔案，通常是src/lib.rs，如果改動了這一位置，可通過path = 新位置實現，比如：

[lib]
name = "portability"
crate-type = ["staticlib", "cdylib"]
path = "src/ios/lib.rs"
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SDK開發的“售後服務”

提供.a/.so給業務團隊，這一過程可能會有人為失誤導致大家對接失敗，下面介紹些我們使用的小技巧。

讀取.a靜態庫的iOS版本

在macOS terminal執行如下命令，用/查詢VERSION。

otool -lv xyz.a | less
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參考：check-ios-deployment-target-of-a-static-library

nm檢視匯出符號

有時編碼疏忽導致沒給需要匯出的C介面新增#[no_mangle]和extern等修飾，或者使用了不合理的優化attribute導致符號被優化掉，此時業務連結我們的庫就會失敗，因此，交付二進位制包前用nm確認符號表是合格的工程師習慣。以下為示例程式碼。

nm -D ./target/release/libportability.so  | grep fun_call_exported_to_c
0000000000003190 T fun_call_exported_to_c
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