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src/boot/start.c

@@ -0,0 +1,74 @@
+#include <def.h>
+#include "console.h"
+#include "multiboot2.h"
+#include "panic.h"
+#include "util.h"
+
+static void *multiboot_find_tag(uptr multiboot_info, u32 type) {
+    uptr next = multiboot_info + 8;
+
+    while (true) {
+        multiboot_tag *tag = (multiboot_tag*)next;
+
+        if (tag->type == MULTIBOOT_TAG_TYPE_END) {
+            return NULL;
+        }
+
+        if (tag->type == type) {
+            return tag;
+        }
+
+        next = align(next + tag->size, MULTIBOOT_TAG_ALIGN);
+    }
+}
+
+#define MAX_REGIONS 64
+
+typedef struct {
+    u64 base_address;
+    u64 length;
+} region;
+
+extern uptr kernel_start;
+extern uptr kernel_end;
+
+static region regions[MAX_REGIONS] = {0};
+static u32 region_count = 0;
+
+static void find_memory_regions(uptr multiboot_info) {
+    multiboot_tag_mmap *tag = multiboot_find_tag(multiboot_info, MULTIBOOT_TAG_TYPE_MMAP);
+    if (tag == NULL) {
+        boot_panic("Multiboot did not provide mmap tag");
+    }
+
+    u32 entry_count = (tag->size - 16) / tag->entry_size;
+    u8 *entry_ptr = (u8*)tag->entries;
+
+    for (u32 i = 0; i < entry_count; ++i) {
+        multiboot_mmap_entry *entry = (multiboot_mmap_entry*)entry_ptr;
+
+        if (entry->type == MULTIBOOT_MEMORY_AVAILABLE) {
+            if (region_count >= MAX_REGIONS) {
+                boot_panic("Too many memory regions");
+            }
+
+            regions[region_count++] = (region){ entry->base_address, entry->length };
+        }
+
+        entry_ptr += tag->entry_size;
+    }
+}
+
+void c_start(u32 magic, uptr multiboot_info) {
+    console_clear();
+
+    if (magic != MULTIBOOT_BOOTLOADER_MAGIC) {
+        boot_panic("Expected bootloader magic 0x%x, but got 0x%x", MULTIBOOT_BOOTLOADER_MAGIC, magic);
+    }
+
+    find_memory_regions(multiboot_info);
+
+    for (u32 i = 0; i < region_count; ++i) {
+        kprintf("base: 0x%X, length: 0x%X\n", regions[i].base_address, regions[i].length);
+    }
+}