Hello world over serial

2025-12-16 23:09:13 +01:00
parent c4c1939637
commit 13fee12f59
23 changed files with 2272 additions and 5 deletions
--- a/kernel/amd64/init.c
+++ b/kernel/amd64/init.c
@@ -0,0 +1,105 @@
+#include <libk/std.h>
+#include <libk/string.h>
+#include <amd64/init.h>
+#include <amd64/tss.h>
+#include <amd64/debug.h>
+
+#define GDT_KCODE     0x08
+#define GDT_KDATA     0x10
+#define GDT_UCODE     0x18
+#define GDT_UDATA     0x20
+#define GDT_TSS       0x28
+
+#define TSS         0x80
+#define TSS_PRESENT 0x89
+
+#define KSTACK_SIZE   (8*1024)
+
+struct gdt_entry {
+  uint16_t limitlow;
+  uint16_t baselow;
+  uint8_t basemid;
+  uint8_t access;
+  uint8_t gran;
+  uint8_t basehigh;
+} __attribute__((packed));
+
+struct gdt_ptr {
+  uint16_t limit;
+  uint64_t base;
+} __attribute__((packed));
+
+struct gdt_extended {
+  struct gdt_entry old[5];
+  struct gdt_entry tsslow;
+  struct gdt_entry tsshigh;
+} __attribute__((packed));
+
+__attribute__((aligned(16))) static volatile uint8_t kernel_stack[KSTACK_SIZE];
+__attribute__((aligned(16))) static volatile struct gdt_extended gdt;
+
+static void amd64_gdt_set(volatile struct gdt_entry *ent, uint32_t base,
+                          uint32_t limit, uint8_t acc, uint8_t gran) {
+  ent->baselow = (base & 0xFFFF);
+  ent->basemid = (base >> 16) & 0xFF;
+  ent->basehigh = (base >> 24) & 0xFF;
+  ent->limitlow = (limit & 0xFFFF);
+  ent->gran = ((limit >> 16) & 0x0F) | (gran & 0xF0);
+  ent->access = acc;
+}
+
+static void amd64_gdt_init(void) {
+  volatile struct tss *tss = amd64_get_tss();
+
+  memset((void *)&gdt, 0, sizeof(gdt));
+  memset((void *)kernel_stack, 0, sizeof(kernel_stack));
+  memset((void *)tss, 0, sizeof(*tss));
+
+  tss->iopb_off = sizeof(*tss);
+  tss->rsp0 = (uint64_t)((uintptr_t)kernel_stack + sizeof(kernel_stack));
+
+  uint64_t tssbase = (uint64_t)&tss;
+  uint64_t tsslimit = sizeof(*tss) - 1;
+
+  amd64_gdt_set(&gdt.old[0], 0, 0, 0, 0);
+  amd64_gdt_set(&gdt.old[1], 0, 0xFFFFF, 0x9A, 0xA0);
+  amd64_gdt_set(&gdt.old[2], 0, 0xFFFFF, 0x92, 0xC0);
+  amd64_gdt_set(&gdt.old[3], 0, 0xFFFFF, 0xFA, 0xA0);
+  amd64_gdt_set(&gdt.old[4], 0, 0xFFFFF, 0xF2, 0xC0);
+  amd64_gdt_set(&gdt.tsslow, (tssbase & 0xFFFFFFFF), tsslimit, TSS_PRESENT | TSS, 0);
+
+  uint32_t tssbasehigh = (tssbase >> 32);
+  gdt.tsshigh.limitlow = (tssbasehigh & 0xFFFF);
+  gdt.tsshigh.baselow = (tssbasehigh >> 16) & 0xFFFF;
+  gdt.tsshigh.basemid = 0;
+  gdt.tsshigh.basehigh = 0;
+  gdt.tsshigh.access = 0;
+  gdt.tsshigh.gran = 0;
+
+  struct gdt_ptr gdtr;
+  gdtr.limit = sizeof(gdt) - 1;
+  gdtr.base = (uint64_t)&gdt;
+  __asm__ volatile("lgdt %0" :: "m"(gdtr) : "memory");
+
+  __asm__ volatile(
+    "pushq %[kcode]\n"
+    "lea 1f(%%rip), %%rax\n"
+    "pushq %%rax\n"
+    "lretq\n"
+    "1:\n"
+    "movw %[kdata], %%ax\n"
+    "movw %%ax, %%ds\n"
+    "movw %%ax, %%es\n"
+    "movw %%ax, %%ss\n"
+    :
+    : [kcode] "i"(GDT_KCODE), [kdata] "i"(GDT_KDATA)
+    : "rax", "memory"
+  );
+
+  __asm__ volatile("ltr %0" :: "r"((uint16_t)GDT_TSS));
+}
+
+void amd64_init(void) {
+  amd64_gdt_init();
+  amd64_debug_init();
+}