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First commit, Vystem v0.1

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2026-03-31 22:15:00 +02:00
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# Kernel bootstrapping using keycard
## Introduction
Shelter being a kernel that need to start with pagging enabled, it need to have a intermediary program to safely jump to it: Keycard. Keycard and Shelter have been designed and thinked for x86-64 only.
## Overview
Keycard is a very simple assembly program with the following role in the following order:
- loading the kernel page table and enabling pagging
- loading and aligning the kernel stack
- jumping to kernel entry point
In order to achieve that, it need to be identity mapped into virtual lower half into the kernel page table, using a physical address provided by UEFI firmware. The bootloader map it into a page (keycard compiled code fit into a single page) with allowed execution but read-only. It also have a kind of 'ABI' which specify which value to put into which register before jumping to Keycard:
- `rax`: should contain the stack top virtual address (VA)
- `rbx`: should contain the physical adrdess of the page table root
- `rcx`: should contain the VA of the kernel entry point
Due to security concerns, the `keycard.bin` file contain the compiled code of Keycard and is stored inside the InitFS with the kernel VYX executable.
The Keycard source code is stored inside `Blastproof/src/keycard.asm`.