diff --git a/README.md b/README.md index a9b345ff..0cf89bf5 100644 --- a/README.md +++ b/README.md @@ -66,6 +66,12 @@ The bootloader crate can be configured through some cargo features: - `map_physical_memory`: Maps the complete physical memory in the virtual address space and passes a [`physical_memory_offset`](https://docs.rs/bootloader/0.4.0/bootloader/bootinfo/struct.BootInfo.html#structfield.physical_memory_offset) field in the `BootInfo`. - The virtual address where the physical memory should be mapped is configurable by setting the `BOOTLOADER_PHYSICAL_MEMORY_OFFSET` environment variable (supports decimal and hex numbers (prefixed with `0x`)). +## Advanced Documentation +See these guides for advanced usage of this crate: + +- [Chainloading](doc/chainloading.md) +- Higher Half Kernel - TODO + ## License Licensed under either of diff --git a/doc/chainloading.md b/doc/chainloading.md new file mode 100644 index 00000000..fa10f35a --- /dev/null +++ b/doc/chainloading.md @@ -0,0 +1,23 @@ +# Chainloading + +Chainloading is a technique that allows one bootloader to call another bootloader as if the system had just booted up. [GNU GRUB](https://www.gnu.org/software/grub/) is one such bootloader which is commonly used for chainloading, as it presents a menu which you can use to select the OS you'd like to boot from. We're using `grub2` here. + +Create a file under `iso/boot/grub/grub.cfg` in the root directory of your OS's source tree. In it, put: + +``` +menuentry "myOS" { + chainloader (hd1)+1 +} +``` + +This tells grub that our binary is installed on the first partition of the `hd1` disk. If you're trying to boot on real hardware you may need to edit this value as appropriate. Alternatively, you should be able to create a partition on the same ISO file that grub creates and copy the binary there. + +Next, create the ISO with: +``` +grub-mkrescue -o grub.iso iso +``` + +Testing with QEMU (replacing `my_os` with the name of your OS's target): +``` +qemu-system-x86_64 -hda grub.iso -hdb target/x86_64-my_os/debug/bootimage-my_os.bin +```