main.c File Reference

Main kernel entry point and primitive UART driver. More...

#include "allocator/kalloc.h"
#include "allocator/page_allocator.h"
#include "asm/asm_helper.h"
#include "drivers/uart.h"
#include "fdt/fdt.h"
#include "icu/icu.h"
#include "linker/symbols.h"
#include "mem_layout/mem_layout.h"
#include "mmu/mmu.h"
#include "page_table/page_table.h"
#include "timer/timer.h"
#include "utils/kprintf.h"
#include "utils/string.h"
#include "utils/utils.h"
#include <libfdt.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>

Include dependency graph for main.c:

Functions
void	switch_to_high_va (void)
	Switch to high virtual addresses.
static void	uart0_putchar (char chr)
	UART0 Character Output Function.
static void	timer_tick_handler (void *priv)
	Test handler invoked on every system timer tick.
static void	setup_system_timer (const void *fdt)
	Configure the system timer to tick once per second.
static void	high_half_main (phy_addr fdt_addr)
	High-half kernel entry, executed AFTER the switch to high VAs.
int	main (const uint64_t *boot_args_ptr)
	Kernel Main Entry Point.

Variables
static uart_device_t	uart0
uint64_t	boot_args [4]
	Captured bootloader arguments.

Detailed Description

Main kernel entry point and primitive UART driver.

Handles early kernel initialization, UART setup, FDT parsing, page allocator bootstrapping, and the transition into the kernel runtime loop.

Author

Abhin Parekadan Jose

Date

2026-04-25

Function Documentation

high_half_main()

static void high_half_main ( phy_addr  fdt_addr )

static

High-half kernel entry, executed AFTER the switch to high VAs.

Must be a separate, non-inlined function so that all PC-relative address materialisation (e.g. &uart0_putchar) happens while the PC is already in the high VA range. It must never return into the low-VA boot/exit path once TTBR0 is disabled.

Never returns: after initialization it parks the core in an infinite wfi loop. The trailing exit(0) is unreachable and exists only to satisfy the compiler/static analysis that every path terminates.

Parameters

fdt_addr

Physical address of the Device Tree Blob, passed through from main().

main()

int main

(

const uint64_t *

boot_args_ptr

)

Kernel Main Entry Point.

Called from primary_entry (boot.s) after the stack has been initialized and the BSS section has been cleared.

Note

On success this function never returns: it hands off to high_half_main()

Parameters

boot_args_ptr

Pointer to an array containing the bootloader arguments passed in registers x0-x3.

Returns

1 on initialization failure (id map setup, UART mapping, or FDT memory map parsing failed). Does not return on success.

setup_system_timer()

static void setup_system_timer ( const void *  fdt )

static

Configure the system timer to tick once per second.

Parameters

fdt	Pointer to the Flattened Device Tree (FDT) blob, which may be used to discover timer properties and configuration.

timer_tick_handler()

static void timer_tick_handler ( void *  priv )

static

Test handler invoked on every system timer tick.

Registered as the tick handler via setup_sys_timer() to verify that the timer driver correctly fires once per configured period.

Parameters

priv	Unused; registered with NULL private data.

uart0_putchar()

static void uart0_putchar ( char  chr )

static

UART0 Character Output Function.

This function is designed to be used as the 'putc' function in the serial_t structure for kprintf. It abstracts the hardware-specific details of writing a character to the UART0 data register.

Parameters

chr	The character to be transmitted over UART0.

Variable Documentation

boot_args

uint64_t boot_args[4]

Captured bootloader arguments.

boot.s only ever saves x0 into boot_args[0]; boot_args[1..3] are never written and simply read as 0 because the array lives in zeroed BSS.

• boot_args[0]: Physical address of the Device Tree Blob (FDT).
• boot_args[1]: Unused (reads as 0 due to BSS zero-init).
• boot_args[2]: Unused (reads as 0 due to BSS zero-init).
• boot_args[3]: Unused (reads as 0 due to BSS zero-init).

uart0

uart_device_t uart0

static

Global UART0 device instance