Rust avr_hal项目使用libc_alloc时链接失败的问题求助

问题描述 #

在对avr_hal项目执行cargo build时，抛出链接错误：

error: linking with avr-gcc failed: exit status: 1

完整错误信息：

WARN rustc_codegen_ssa::back::link Linker does not support -no-pie command line option. Retrying without.
error: linking with `avr-gcc` failed: exit status: 1
  |
  = note: LC_ALL="C" PATH="/usr/local/rustup/toolchains/nightly-2023-08-08-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/vscode/vscode-server/bin/linux-x64/74f6148eb9ea00507ec113ec51c489d6ffb4b771/bin/remote-cli:/usr/local/cargo/bin:/usr/local/cargo/bin:/usr/local/cargo/bin:/usr/local/cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/home/vscode/.local/bin" VSLANG="1033" "avr-gcc" "-mmcu=atmega328p" "/tmp/rustcfZfdOa/symbols.o" "/workspaces/avrgcc_linking_fail_mre/avrgcc-linking-failed-mre/target/avr-atmega328p/debug/deps/avrgcc_linking_failed_mre-4f3e20c93dc596f3.arduino_hal-6541d5c2c9fe98bb.arduino_hal.fa13f7103336eb93-cgu.0.rcgu.o.rcgu.o" "-Wl,--as-needed" "-L" "/workspaces/avrgcc_linking_fail_mre/avrgcc-linking-failed-mre/target/avr-atmega328p/debug/deps" "-L" "/workspaces/avrgcc_linking_fail_mre/avrgcc-linking-failed-mre/target/debug/deps" "-L" "/usr/local/rustup/toolchains/nightly-2023-08-08-x86_64-unknown-linux-gnu/lib/rustlib/avr-atmega328p/lib" "-Wl,-Bstatic" "/workspaces/avrgcc_linking_fail_mre/avrgcc-linking-failed-mre/target/avr-atmega328p/debug/deps/libcompiler_builtins-400b15d51260279e.rlib" "-Wl,-Bdynamic" "-lgcc" "-Wl,-z,noexecstack" "-L" "/usr/local/rustup/toolchains/nightly-2023-08-08-x86_64-unknown-linux-gnu/lib/rustlib/avr-atmega328p/lib" "-o" "/workspaces/avrgcc_linking_fail_mre/avrgcc-linking-failed-mre/target/avr-atmega328p/debug/deps/avrgcc_linking_failed_mre-4f3e20c93dc596f3.elf" "-Wl,--gc-sections"
  = note: /workspaces/avrgcc_linking_fail_mre/avrgcc-linking-failed-mre/target/avr-atmega328p/debug/deps/avrgcc_linking_failed_mre-4f3e20c93dc596f3.arduino_hal-6541d5c2c9fe98bb.arduino_hal.fa13f7103336eb93-cgu.0.rcgu.o.rcgu.o: In function `_$LT$libc_alloc..LibcAlloc$u20$as$u20$core..alloc..global..GlobalAlloc$GT$::alloc::hcb8d6e5a6803e71c':
          /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/libc_alloc-1.0.5/src/lib.rs:35: undefined reference to `memalign'
          /workspaces/avrgcc_linking_fail_mre/avrgcc-linking-failed-mre/target/avr-atmega328p/debug/deps/avrgcc_linking_failed_mre-4f3e20c93dc596f3.arduino_hal-6541d5c2c9fe98bb.arduino_hal.fa13f7103336eb93-cgu.0.rcgu.o.rcgu.o: In function `alloc::raw_vec::finish_grow::h0af711d7dce70706':
          arduino_hal.fa13f7103336eb93-cgu.0:(.text._ZN5alloc7raw_vec11finish_grow17h0af711d7dce70706E+0xb2): undefined reference to `memalign'
          collect2: error: ld returned 1 exit status
          
  = 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)

复现步骤 #

• 安装cargo-generate：执行 cargo install cargo-generate
• 生成avr-hal项目：cargo generate --git https://github.com/rahix/avr-hal-template.git --name avrgcc-linking-failed-mre（选择Uno开发板）
• 添加.cargo/config.toml配置文件：

  [build]
  target = "avr-specs/avr-atmega328p.json"
  
  [unstable]
  build-std = ["core", "alloc"]
  

• 修改src/main.rs内容：

  #![no_std]
  #![no_main]
  
  use libc_alloc::LibcAlloc;
  use panic_halt as _;
  
  extern crate alloc;
  
  
  #[arduino_hal::entry]
  fn main() -> ! {
      "123".replace("1", "4");
      loop {}
  }
  
  #[global_allocator]
  static ALLOCATOR: LibcAlloc = LibcAlloc;
  

• 在Cargo.toml依赖中添加：libc_alloc = "1.0.5"
• （可选）使用开发容器的话，添加.devcontainer/devcontainer.json：

  {
      "name": "avrgcc_linking_fail_mre_devcontainer",
      "dockerFile": "Dockerfile"
  }
  

• （可选）添加.devcontainer/Dockerfile：

  FROM mcr.microsoft.com/devcontainers/rust:1-1-bullseye
  
  RUN apt update
  
  RUN apt install -y fish
  RUN apt install -y avr-libc gcc-avr pkg-config avrdude libudev-dev build-essential
  
  RUN cargo install cargo-generate
  

• 构建开发容器后，进入项目目录执行cargo build或cargo build --release触发错误

问题成因 #

错误核心是undefined reference to memalign：

• libc_alloc crate依赖标准libc中的memalign函数实现内存分配，但AVR平台的avr-libc并未提供该函数
• AVR属于资源受限的嵌入式平台，其libc仅实现了基础内存分配函数（如malloc、free），没有memalign这类对齐分配的函数，导致链接时找不到对应符号

修复方法 #

方法1：使用AVR专用全局分配器 #

替换libc_alloc为适配AVR的分配器，比如avr-alloc：

1. 移除Cargo.toml中的libc_alloc依赖，添加：

   avr-alloc = "0.2.0"
   

2. 修改src/main.rs，初始化AVR堆并设置全局分配器：

   #![no_std]
   #![no_main]
   
   use avr_alloc::AvrAlloc;
   use panic_halt as _;
   
   extern crate alloc;
   
   #[global_allocator]
   static ALLOCATOR: AvrAlloc = AvrAlloc;
   
   #[arduino_hal::entry]
   fn main() -> ! {
       // 初始化堆：指定堆的起始地址和大小
       // 对于Atmega328p，SRAM总大小2KB，这里预留部分给栈，设置堆大小1KB
       unsafe {
           avr_alloc::init_allocator(0x800200, 1024);
       }
   
       let _modified_str = "123".replace("1", "4");
       loop {}
   }
   

方法2：使用无动态分配的替代方案 #

AVR资源有限，动态内存分配易引发碎片化问题，推荐使用heapless crate提供的固定大小容器：

1. 添加heapless依赖：

   heapless = { version = "0.8", features = ["alloc"] }
   

2. 修改代码使用heapless::String替代标准库字符串：

   #![no_std]
   #![no_main]
   
   use heapless::String;
   use panic_halt as _;
   
   #[arduino_hal::entry]
   fn main() -> ! {
       let mut s: String<32> = "123".into();
       s.replace_range(0..1, "4");
       loop {}
   }
   

   这种方式无需全局分配器，更适配AVR这类嵌入式设备。

关于AVR-Hal中使用全局分配器 #

可以使用，但必须选择适配AVR架构的分配器实现，不能直接使用针对桌面/服务器libc的分配器（如libc_alloc）。AVR的内存模型与标准系统差异较大，需要使用专门为其编写的分配器，或自行基于AVR的SRAM实现简单分配逻辑。

内容的提问来源于stack exchange，提问作者cico