# AArch64 UEFI bootstraps

Copyright (c) 2011-2013 ARM Limited. All rights reserved. See the `LICENSE.TXT` file for more information.

Contents:

- Introduction
- Build
- Use on ARMv8 RTSM and FVP models
- Use on ARMv8 Foundation model

## Introduction

A bootstrap can be used to change the model state, like the Exception Level (EL), before executing the UEFI binary.

For the ARMv8 RTSM and FVP models this can be used to show/test the UEFI binary starting at different exception levels. The ARMv8 models start at EL3 by default.

In the case of the Foundation model a bootstrap is required to jump to the UEFI binary as loaded in RAM. This is required as the Foundation model cannot load and execute UEFI binaries directly. The Foundation model can only load and execute ELF binaries.

## Build

Build the bootstraps using a AArch64 GCC cross-compiler. By default the `Makefile` is configured to assume a GCC bare-metal toolchain:

    PATH=$PATH:<path/to/baremetal-tools/bin/> make clean
    PATH=$PATH:<path/to/baremetal-tools/bin/> make

To build the bootstraps with a Linux GCC toolchain use the following commands:

    PATH=$PATH:<path/to/aarch64-linux-gnu-tools/bin/> make clean
    PATH=$PATH:<path/to/aarch64-linux-gnu-tools/bin/> CROSS_COMPILE=<gcc-prefix> make

The `gcc-prefix` depends on the specific toolchain distribution used. It can be "aarch64-linux-gnu-" for example.

This will result in four `axf` files:

- uefi-bootstrap-el3 : The bootstrap jumps to the UEFI code in FLASH without changing anything.

- uefi-bootstrap-el2 : Setup EL3 and switch the model to EL2 before jumping to the UEFI code in FLASH.

- uefi-bootstrap-el1 : Setup EL3 and prepare to run at non-secure EL1. Switch to non-secure EL1 and run the UEFI code in FLASH.

- uefi-bootstrap-el3-foundation : The bootstrap jumps to the UEFI code in RAM without changing anything. Only to be used with the Foundation model. The Foundation model does not have non-secure memory at address `0x0` and thus the UEFI image should be pre-loaded into non-secure RAM at address `0xA0000000`.

## Use on ARMv8 RTSM and FVP models

Add the '-a' option to the model start script and point to the required bootstrap:

    < ... model start script as described in top-level readme file ... >
     -a <path/to/bootstrap-binary-file>

NOTE: The Foundation model bootstrap should not be used with these models.

## Use on ARMv8 Foundation model

The Foundation model takes an option for an ELF file to be loaded as well as an option to load a binary data blob into RAM. This can be used to run UEFI in the following manner:

    <PATH_TO_INSTALLED_FOUNDATION_MODEL>/Foundation_v8 --cores=2 --visualization
      --image=uefi-bootstrap-el3-foundation.axf --nsdata=RTSM_VE_FOUNDATIONV8_EFI.fd@0xA0000000

NOTE: The RTSM version of the bootstraps and UEFI image will not work as expected on the Foundation model. Foundation model specific versions should be used.