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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 multiboot_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 multiboot_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, data, size);
offset += size;
return MB1_LOAD_ADDRESS + (size - offset);
}
// Load the mb1 structs into memory
static void mb1_load(struct multiboot_entry *entry)
{
(void)mb1_store;
(void)entry;
}
// 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 multiboot_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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