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The no_mangle attribute is unsafe since Rust 2024

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Philipp Oppermann
2025-03-27 15:39:15 +01:00
parent 9345886d44
commit 9753695744
47 changed files with 149 additions and 149 deletions
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6
blog/content/edition-2/posts/01-freestanding-rust-binary/index.md
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@@ -213,13 +213,13 @@ fn panic(_info: &PanicInfo) -> ! {
You might notice that we removed the `main` function. The reason is that a `main` doesn't make sense without an underlying runtime that calls it. Instead, we are now overwriting the operating system entry point with our own `_start` function:
```rust
#[no_mangle]
#[unsafe(no_mangle)]
pub extern "C" fn _start() -> ! {
loop {}
}
```
By using the `#[no_mangle]` attribute, we disable [name mangling] to ensure that the Rust compiler really outputs a function with the name `_start`. Without the attribute, the compiler would generate some cryptic `_ZN3blog_os4_start7hb173fedf945531caE` symbol to give every function a unique name. The attribute is required because we need to tell the name of the entry point function to the linker in the next step.
By using the `#[unsafe(no_mangle)]` attribute, we disable [name mangling] to ensure that the Rust compiler really outputs a function with the name `_start`. Without the attribute, the compiler would generate some cryptic `_ZN3blog_os4_start7hb173fedf945531caE` symbol to give every function a unique name. The attribute is required because we need to tell the name of the entry point function to the linker in the next step.
We also have to mark the function as `extern "C"` to tell the compiler that it should use the [C calling convention] for this function (instead of the unspecified Rust calling convention). The reason for naming the function `_start` is that this is the default entry point name for most systems.
@@ -463,7 +463,7 @@ A minimal freestanding Rust binary looks like this:
use core::panic::PanicInfo;
#[no_mangle] // don't mangle the name of this function
#[unsafe(no_mangle)] // don't mangle the name of this function
pub extern "C" fn _start() -> ! {
// this function is the entry point, since the linker looks for a function
// named `_start` by default