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// MIT License, Copyright (c) 2021 Marvin Borner
// Everything according to spec
#include <elf.h>
#include <impl/mb1.h>
#include <lib.h>
#include <pnc.h>
// The address where data gets stored
#define MB1_LOAD_ADDRESS 0x10000
struct mb1_entry {
u32 magic;
u32 flags;
u32 checksum; // Everything after that is optional
u32 header_addr;
u32 load_addr;
u32 load_end_addr;
u32 bss_end_addr;
u32 entry_addr;
u32 mode_type;
u32 width;
u32 height;
u32 depth;
};
// The (really simple) multiboot checksum algorithm
static u32 mb1_checksum(struct mb1_entry *entry)
{
return -(entry->magic + entry->flags);
}
// Load data into memory and return address (not overlapping
static u32 mb1_store(void *data, u32 size)
{
static u32 offset = 0;
memcpy((void *)(MB1_LOAD_ADDRESS + offset), data, size);
offset += size;
return MB1_LOAD_ADDRESS + (offset - size);
}
// Load the mb1 structs into memory
static void mb1_load(struct mb1_entry *entry)
{
(void)entry;
struct mb1_info info_struct = { 0 };
struct mb1_info *info = (void *)mb1_store(&info_struct, sizeof(info_struct));
// Set boot device
info->flags |= MB1_INFO_BOOTDEV;
info->boot_device = boot_disk;
// Set bootloader name
info->flags |= MB1_INFO_BOOT_LOADER_NAME;
char loader_name[] = "SegelBoot";
info->boot_loader_name = mb1_store(loader_name, sizeof(loader_name));
}
// Jump to kernel with correct info pointer in eax
static void mb1_jump(u32 entry, u32 info)
{
log("Jumping. So long and thanks for all the fish!\n");
// Move and jump!
__asm__ volatile("movl $" STRINGIFY(MB1_LOAD_MAGIC) ", %%eax\n\t"
"jmpl *%%edi\n\t"
:
: "D"(entry), "b"(info)
: "memory");
panic("Jumper returned\n");
}
// Detect and verify mb1
u8 mb1_detect(struct cfg_entry *cfg)
{
u8 header[8192] = { 0 };
s32 ret = cfg->dev->p.disk.fs.read(cfg->path, header, 0, sizeof(header), cfg->dev);
if (ret < 12)
return 0;
// Find start of multiboot entry by searching for magic
struct mb1_entry *entry = 0;
for (u32 i = 0; i < sizeof(header); i++) {
u32 *p = (u32 *)&header[i];
if (*p == MB1_MAGIC) {
entry = (void *)p;
break;
}
}
if (!entry)
return 0;
u32 checksum = mb1_checksum(entry);
if (checksum != entry->checksum)
return 0;
cfg->impl.type = IMPL_MB1;
cfg->impl.start = entry;
return 1;
}
#include <pic.h>
// Execute mb1 type kernel
void mb1_exec(struct cfg_entry *cfg)
{
u32 entry = elf_load(cfg->dev, cfg->path);
mb1_load(cfg->impl.start);
// This is a kind of hacky parameter stack pushing thing, just disable warning :)
#pragma GCC diagnostic ignored "-Wpedantic"
jmp_kernel((void *)mb1_jump, 2, entry, MB1_LOAD_ADDRESS);
#pragma GCC diagnostic pop
}
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