// SPDX-License-Identifier: MIT OR Apache-2.0
//
// Copyright (c) 2021-2023 Andre Richter <andre.o.richter@gmail.com>
//--------------------------------------------------------------------------------------------------
// Definitions
//--------------------------------------------------------------------------------------------------
// Load the address of a symbol into a register, PC-relative.
//
// The symbol must lie within +/- 4 GiB of the Program Counter.
//
// # Resources
//
// - https://sourceware.org/binutils/docs-2.36/as/AArch64_002dRelocations.html
.macro ADR_REL register, symbol
adrp \register, \symbol
add \register, \register, #:lo12:\symbol
.endm
// Load the address of a symbol into a register, absolute.
//
// # Resources
//
// - https://sourceware.org/binutils/docs-2.36/as/AArch64_002dRelocations.html
.macro ADR_ABS register, symbol
movz \register, #:abs_g3:\symbol
movk \register, #:abs_g2_nc:\symbol
movk \register, #:abs_g1_nc:\symbol
movk \register, #:abs_g0_nc:\symbol
.endm
//--------------------------------------------------------------------------------------------------
// Public Code
//--------------------------------------------------------------------------------------------------
.section .text._start
//------------------------------------------------------------------------------
// fn _start()
//------------------------------------------------------------------------------
_start:
// Only proceed if the core executes in EL2. Park it otherwise.
mrs x0, CurrentEL
cmp x0, {CONST_CURRENTEL_EL2}
b.ne .L_parking_loop
// Only proceed on the boot core. Park it otherwise.
mrs x1, MPIDR_EL1
and x1, x1, {CONST_CORE_ID_MASK}
ldr x2, BOOT_CORE_ID // provided by bsp/__board_name__/cpu.rs
cmp x1, x2
b.ne .L_parking_loop
// If execution reaches here, it is the boot core.
// Initialize DRAM.
ADR_REL x0, __bss_start
ADR_REL x1, __bss_end_exclusive
.L_bss_init_loop:
cmp x0, x1
b.eq .L_prepare_rust
stp xzr, xzr, [x0], #16
b .L_bss_init_loop
// Prepare the jump to Rust code.
.L_prepare_rust:
// Load the base address of the kernel's translation tables.
ldr x0, PHYS_KERNEL_TABLES_BASE_ADDR // provided by bsp/__board_name__/memory/mmu.rs
// Load the _absolute_ addresses of the following symbols. Since the kernel is linked at
// the top of the 64 bit address space, these are effectively virtual addresses.
ADR_ABS x1, __boot_core_stack_end_exclusive
ADR_ABS x2, kernel_entry
// Load the PC-relative address of the stack and set the stack pointer.
//
// Since _start() is the first function that runs after the firmware has loaded the kernel
// into memory, retrieving this symbol PC-relative returns the "physical" address.
//
// Setting the stack pointer to this value ensures that anything that still runs in EL2,
// until the kernel returns to EL1 with the MMU enabled, works as well. After the return to
// EL1, the virtual address of the stack retrieved above will be used.
ADR_REL x3, __boot_core_stack_end_exclusive
mov sp, x3
// Read the CPU's timer counter frequency and store it in ARCH_TIMER_COUNTER_FREQUENCY.
// Abort if the frequency read back as 0.
ADR_REL x4, ARCH_TIMER_COUNTER_FREQUENCY // provided by aarch64/time.rs
mrs x5, CNTFRQ_EL0
cmp x5, xzr
b.eq .L_parking_loop
str w5, [x4]
// Jump to Rust code. x0, x1 and x2 hold the function arguments provided to _start_rust().
b _start_rust
// Infinitely wait for events (aka "park the core").
.L_parking_loop:
wfe
b .L_parking_loop
.size _start, . - _start
.type _start, function
.global _start