mirror of https://github.com/tailix/libkernaux.git
119 lines
4.8 KiB
C
119 lines
4.8 KiB
C
#include <stdint.h>
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#include <stddef.h>
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#include <kernaux/console.h>
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#include "stivale2.h"
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static void poweroff();
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// We need to tell the stivale bootloader where we want our stack to be.
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// We are going to allocate our stack as an array in .bss.
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static uint8_t stack[8192];
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// stivale2 uses a linked list of tags for both communicating TO the
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// bootloader, or receiving info FROM it. More information about these tags
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// is found in the stivale2 specification.
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// stivale2 offers a runtime terminal service which can be ditched at any
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// time, but it provides an easy way to print out to graphical terminal,
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// especially during early boot.
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// Read the notes about the requirements for using this feature below this
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// code block.
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static struct stivale2_header_tag_terminal terminal_hdr_tag = {
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// All tags need to begin with an identifier and a pointer to the next tag.
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.tag = {
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// Identification constant defined in stivale2.h and the specification.
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.identifier = STIVALE2_HEADER_TAG_TERMINAL_ID,
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// If next is 0, it marks the end of the linked list of header tags.
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.next = 0
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},
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// The terminal header tag possesses a flags field, leave it as 0 for now
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// as it is unused.
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.flags = 0
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};
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// We are now going to define a framebuffer header tag.
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// This tag tells the bootloader that we want a graphical framebuffer instead
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// of a CGA-compatible text mode. Omitting this tag will make the bootloader
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// default to text mode, if available.
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static struct stivale2_header_tag_framebuffer framebuffer_hdr_tag = {
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// Same as above.
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.tag = {
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.identifier = STIVALE2_HEADER_TAG_FRAMEBUFFER_ID,
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// Instead of 0, we now point to the previous header tag. The order in
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// which header tags are linked does not matter.
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.next = (uint64_t)&terminal_hdr_tag
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},
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// We set all the framebuffer specifics to 0 as we want the bootloader
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// to pick the best it can.
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.framebuffer_width = 0,
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.framebuffer_height = 0,
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.framebuffer_bpp = 0
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};
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// The stivale2 specification says we need to define a "header structure".
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// This structure needs to reside in the .stivale2hdr ELF section in order
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// for the bootloader to find it. We use this __attribute__ directive to
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// tell the compiler to put the following structure in said section.
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__attribute__((section(".stivale2hdr"), used))
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static struct stivale2_header stivale_hdr = {
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// The entry_point member is used to specify an alternative entry
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// point that the bootloader should jump to instead of the executable's
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// ELF entry point. We do not care about that so we leave it zeroed.
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.entry_point = 0,
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// Let's tell the bootloader where our stack is.
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// We need to add the sizeof(stack) since in x86(_64) the stack grows
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// downwards.
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.stack = (uintptr_t)stack + sizeof(stack),
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// Bit 1, if set, causes the bootloader to return to us pointers in the
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// higher half, which we likely want since this is a higher half kernel.
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// Bit 2, if set, tells the bootloader to enable protected memory ranges,
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// that is, to respect the ELF PHDR mandated permissions for the executable's
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// segments.
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// Bit 3, if set, enables fully virtual kernel mappings, which we want as
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// they allow the bootloader to pick whichever *physical* memory address is
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// available to load the kernel, rather than relying on us telling it where
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// to load it.
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// Bit 4 disables a deprecated feature and should always be set.
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.flags = (1 << 1) | (1 << 2) | (1 << 3) | (1 << 4),
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// This header structure is the root of the linked list of header tags and
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// points to the first one in the linked list.
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.tags = (uintptr_t)&framebuffer_hdr_tag
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};
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// We will now write a helper function which will allow us to scan for tags
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// that we want FROM the bootloader (structure tags).
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void *stivale2_get_tag(struct stivale2_struct *stivale2_struct, uint64_t id) {
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struct stivale2_tag *current_tag = (void *)stivale2_struct->tags;
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for (;;) {
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// If the tag pointer is NULL (end of linked list), we did not find
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// the tag. Return NULL to signal this.
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if (current_tag == NULL) {
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return NULL;
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}
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// Check whether the identifier matches. If it does, return a pointer
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// to the matching tag.
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if (current_tag->identifier == id) {
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return current_tag;
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}
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// Get a pointer to the next tag in the linked list and repeat.
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current_tag = (void *)current_tag->next;
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}
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}
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// The following will be our kernel's entry point.
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void _start(struct stivale2_struct *stivale2_struct __attribute__((unused))) {
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kernaux_console_puts("Hello, World!");
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poweroff();
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}
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void poweroff()
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{
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const uint16_t port = 0x604;
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const uint16_t value = 0x2000;
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__asm__ volatile("outw %1, %0" : : "dN" (port), "a" (value));
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}
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