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Update Linux/Windows/Mac entry points

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Philipp Oppermann
2018-02-09 15:47:59 +01:00
parent 5e96335c23
commit 254d5476b1
1 changed files with 38 additions and 14 deletions
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52
blog/content/second-edition/posts/01-freestanding-rust-binary/index.md
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@@ -131,9 +131,8 @@ fn main() {}
#[lang = "panic_fmt"] #[lang = "panic_fmt"]
#[no_mangle] #[no_mangle]
pub extern fn rust_begin_panic(_msg: core::fmt::Arguments, pub extern fn rust_begin_panic(_msg: core::fmt::Arguments,
_file: &'static str, _file: &'static str, _line: u32, _column: u32) -> !
_line: u32, {
_column: u32) -> ! {
loop {} loop {}
} }
``` ```
@@ -213,7 +212,7 @@ On Linux, the default entry point is called `_start`. The linker just looks for
```rust ```rust
#[no_mangle] #[no_mangle]
pub fn _start() -> ! { pub extern fn _start() -> ! {
loop {} loop {}
} }
``` ```
@@ -260,16 +259,16 @@ One way to pass linker attributes via cargo is the `cargo rustc` command. The co
With this command, our crate builds again as a freestanding executable! With this command, our crate builds again as a freestanding executable!
#### Windows #### Windows
On Windows, the linker requires two entry points: `WinMain` and `WinMainCRTStartup`. The one that actually is called is `WinMainCRTStartup`. Like on Linux, we overwrite the entry points by defining `no_mangle` functions: On Windows, the linker requires two entry points: `WinMain` and `WinMainCRTStartup`, [depending on the used subsystem](https://msdn.microsoft.com/en-us/library/f9t8842e.aspx). Like on Linux, we overwrite the entry points by defining `no_mangle` functions:
```rust ```rust
#[no_mangle] #[no_mangle]
pub fn WinMainCRTStartup() -> ! { pub extern fn WinMainCRTStartup() -> ! {
WinMain(); WinMain();
} }
#[no_mangle] #[no_mangle]
pub fn WinMain() -> ! { pub extern fn WinMain() -> ! {
loop {} loop {}
} }
``` ```
@@ -277,7 +276,23 @@ pub fn WinMain() -> ! {
We just call `WinMain` from `WinMainCRTStartup` to avoid any ambiguity which function is called. We just call `WinMain` from `WinMainCRTStartup` to avoid any ambiguity which function is called.
#### OS X #### OS X
TODO: I don't have access to a Mac at the moment. In case you know the entry point procedure on Mac and would like to help, please send a pull request! Mac OS X [does not support statically linked binaries], so we have to link the `libSystem` library. The entry point is the called `main`:
[does not support statically linked binaries]: https://developer.apple.com/library/content/qa/qa1118/_index.html
```rust
#[no_mangle]
pub extern fn main() -> ! {
loop {}
}
```
To build it and link `libSystem`, we execute:
```
> cargo rustc -- -Z pre-link-arg=-lSystem
```
## Summary ## Summary
@@ -300,7 +315,7 @@ pub extern fn rust_begin_panic(_msg: core::fmt::Arguments,
// On Linux: // On Linux:
#[no_mangle] // don't mangle the name of this function #[no_mangle] // don't mangle the name of this function
pub fn _start() -> ! { pub extern fn _start() -> ! {
// this function is the entry point, since the linker looks for a function // this function is the entry point, since the linker looks for a function
// named `_start_` by default // named `_start_` by default
loop {} loop {}
@@ -308,17 +323,21 @@ pub fn _start() -> ! {
// On Windows: // On Windows:
#[no_mangle] #[no_mangle]
pub fn WinMainCRTStartup() -> ! { pub extern fn WinMainCRTStartup() -> ! {
WinMain(); WinMain();
} }
#[no_mangle] #[no_mangle]
pub fn WinMain() -> ! { pub extern fn WinMain() -> ! {
loop {} loop {}
} }
// On Mac: // On Mac:
// TODO
#[no_mangle]
pub extern fn main() -> ! {
loop {}
}
``` ```
`Cargo.toml`: `Cargo.toml`:
@@ -340,8 +359,13 @@ panic = "abort" # disable stack unwinding on panic
It can be compiled with: It can be compiled with:
``` ```bash
cargo rustc -- -Z pre-link-arg=-nostartfiles # Linux
> cargo rustc -- -Z pre-link-arg=-nostartfiles
# Windows
> cargo build
# Mac
> cargo rustc -- -Z pre-link-arg=-lSystem
``` ```
Note that this is just a minimal example of a freestanding Rust binary. This binary expects various things, for example that a stack is initialized when the `_start` function is called. **So for any real use of such a binary, more steps are required**. Note that this is just a minimal example of a freestanding Rust binary. This binary expects various things, for example that a stack is initialized when the `_start` function is called. **So for any real use of such a binary, more steps are required**.