Macro bootloader_api::entry_point

macro_rules! entry_point {
    ($path:path) => { ... };
    ($path:path, config = $config:expr) => { ... };
}

Defines the entry point function.

The function must have the signature fn(&'static mut BootInfo) -> !.

This macro just creates a function named _start, which the linker will use as the entry point. The advantage of using this macro instead of providing an own _start function is that the macro ensures that the function and argument types are correct.

Configuration

This macro supports an optional second parameter to configure how the bootloader should boot the kernel. The second parameter needs to be given as config = ... and be of type &BootloaderConfig. If not given, the configuration defaults to BootloaderConfig::new_default.

Examples

• With default configuration:

  #![no_std]
  #![no_main]
  
  bootloader_api::entry_point!(main);
  
  fn main(bootinfo: &'static mut bootloader_api::BootInfo) -> ! {
      loop {}
  }
  
  #[panic_handler]
  fn panic(_info: &core::panic::PanicInfo) -> ! {
      loop {}
  }
  

  The name of the entry point function does not matter. For example, instead of main, we could also name it fn my_entry_point(...) -> !. We would then need to specify entry_point!(my_entry_point) of course.

• With custom configuration:

  #![no_std]
  #![no_main]
  
  use bootloader_api::{entry_point, BootloaderConfig};
   
  pub static BOOTLOADER_CONFIG: BootloaderConfig = {
      let mut config = BootloaderConfig::new_default();
      config.frame_buffer.minimum_framebuffer_height = Some(720);
      config
  };
  
  entry_point!(main, config = &BOOTLOADER_CONFIG);
  
  fn main(bootinfo: &'static mut bootloader_api::BootInfo) -> ! {
      loop {}
  }
  
  #[panic_handler]
  fn panic(_info: &core::panic::PanicInfo) -> ! {
      loop {}
  }
  

Implementation Notes

• Start function: The entry_point macro generates a small wrapper function named _start (without name mangling) that becomes the actual entry point function of the executable. This function doesn’t do anything itself, it just calls into the function that is provided as macro argument. The purpose of this function is to use the correct ABI and parameter types required by this crate. A user-provided _start function could silently become incompatible on dependency updates since the Rust compiler cannot check the signature of custom entry point functions.
• Configuration: Behind the scenes, the configuration struct is serialized using BootloaderConfig::serialize. The resulting byte array is then stored as a static variable annotated with #[link_section = ".bootloader-config"], which instructs the Rust compiler to store it in a special section of the resulting ELF executable. From there, the bootloader will automatically read it when loading the kernel.