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Merge pull request #478 from ehuss/fix-start
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Remove `#![start]` attribute
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ehuss authored Jan 23, 2025
2 parents d2c1d5c + 3253190 commit e031105
Showing 1 changed file with 3 additions and 39 deletions.
42 changes: 3 additions & 39 deletions src/beneath-std.md
Original file line number Diff line number Diff line change
Expand Up @@ -30,46 +30,10 @@ We will probably need a nightly version of the compiler to produce
a `#![no_std]` executable because on many platforms, we have to provide the
`eh_personality` [lang item], which is unstable.

Controlling the entry point is possible in two ways: the `#[start]` attribute,
or overriding the default shim for the C `main` function with your own.
Additionally, it's required to define a [panic handler function](panic-handler.html).

The function marked `#[start]` is passed the command line parameters
in the same format as C (aside from the exact integer types being used):

```rust
#![feature(start, lang_items, core_intrinsics, rustc_private)]
#![allow(internal_features)]
#![no_std]
You will need to define a symbol for the entry point that is suitable for your target. For example, `main`, `_start`, `WinMain`, or whatever starting point is relevant for your target.
Additionally, you need to use the `#![no_main]` attribute to prevent the compiler from attempting to generate an entry point itself.

// Necessary for `panic = "unwind"` builds on cfg(unix) platforms.
#![feature(panic_unwind)]
extern crate unwind;

// Pull in the system libc library for what crt0.o likely requires.
#[cfg(not(windows))]
extern crate libc;

use core::panic::PanicInfo;

// Entry point for this program.
#[start]
fn main(_argc: isize, _argv: *const *const u8) -> isize {
0
}

// These functions are used by the compiler, but not for an empty program like this.
// They are normally provided by `std`.
#[lang = "eh_personality"]
fn rust_eh_personality() {}
#[panic_handler]
fn panic_handler(_info: &PanicInfo) -> ! { core::intrinsics::abort() }
```

To override the compiler-inserted `main` shim, we have to disable it
with `#![no_main]` and then create the appropriate symbol with the
correct ABI and the correct name, which requires overriding the
compiler's name mangling too:
Additionally, it's required to define a [panic handler function](panic-handler.html).

```rust
#![feature(lang_items, core_intrinsics, rustc_private)]
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