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101 lines
3.2 KiB
ArmAsm
101 lines
3.2 KiB
ArmAsm
// SPDX-License-Identifier: MIT OR Apache-2.0
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//
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// Copyright (c) 2021-2022 Andre Richter <andre.o.richter@gmail.com>
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//--------------------------------------------------------------------------------------------------
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// Definitions
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//--------------------------------------------------------------------------------------------------
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// Load the address of a symbol into a register, PC-relative.
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//
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// The symbol must lie within +/- 4 GiB of the Program Counter.
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//
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// # Resources
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//
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// - https://sourceware.org/binutils/docs-2.36/as/AArch64_002dRelocations.html
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.macro ADR_REL register, symbol
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adrp \register, \symbol
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add \register, \register, #:lo12:\symbol
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.endm
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// Load the address of a symbol into a register, absolute.
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//
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// # Resources
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//
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// - https://sourceware.org/binutils/docs-2.36/as/AArch64_002dRelocations.html
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.macro ADR_ABS register, symbol
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movz \register, #:abs_g3:\symbol
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movk \register, #:abs_g2_nc:\symbol
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movk \register, #:abs_g1_nc:\symbol
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movk \register, #:abs_g0_nc:\symbol
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.endm
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.equ _EL2, 0x8
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.equ _core_id_mask, 0b11
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//--------------------------------------------------------------------------------------------------
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// Public Code
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//--------------------------------------------------------------------------------------------------
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.section .text._start
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//------------------------------------------------------------------------------
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// fn _start()
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//------------------------------------------------------------------------------
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_start:
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// Only proceed if the core executes in EL2. Park it otherwise.
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mrs x0, CurrentEL
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cmp x0, _EL2
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b.ne .L_parking_loop
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// Only proceed on the boot core. Park it otherwise.
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mrs x1, MPIDR_EL1
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and x1, x1, _core_id_mask
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ldr x2, BOOT_CORE_ID // provided by bsp/__board_name__/cpu.rs
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cmp x1, x2
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b.ne .L_parking_loop
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// If execution reaches here, it is the boot core.
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// Initialize DRAM.
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ADR_REL x0, __bss_start
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ADR_REL x1, __bss_end_exclusive
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.L_bss_init_loop:
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cmp x0, x1
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b.eq .L_prepare_rust
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stp xzr, xzr, [x0], #16
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b .L_bss_init_loop
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// Prepare the jump to Rust code.
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.L_prepare_rust:
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// Load the base address of the kernel's translation tables.
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ldr x0, PHYS_KERNEL_TABLES_BASE_ADDR // provided by bsp/__board_name__/memory/mmu.rs
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// Load the _absolute_ addresses of the following symbols. Since the kernel is linked at
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// the top of the 64 bit address space, these are effectively virtual addresses.
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ADR_ABS x1, __boot_core_stack_end_exclusive
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ADR_ABS x2, kernel_init
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// Load the PC-relative address of the stack and set the stack pointer.
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//
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// Since _start() is the first function that runs after the firmware has loaded the kernel
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// into memory, retrieving this symbol PC-relative returns the "physical" address.
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//
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// Setting the stack pointer to this value ensures that anything that still runs in EL2,
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// until the kernel returns to EL1 with the MMU enabled, works as well. After the return to
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// EL1, the virtual address of the stack retrieved above will be used.
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ADR_REL x4, __boot_core_stack_end_exclusive
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mov sp, x4
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// Jump to Rust code. x0, x1 and x2 hold the function arguments provided to _start_rust().
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b _start_rust
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// Infinitely wait for events (aka "park the core").
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.L_parking_loop:
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wfe
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b .L_parking_loop
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.size _start, . - _start
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.type _start, function
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.global _start
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