wtorek

.gitignore

@@ -0,0 +1,3 @@
+/kernel
+/loader
+*.o

Makefile

@@ -1,6 +1,6 @@
 all: kernel loader
 
-OBJS := main.o
+OBJS := main.o gdt.o page.o
 
 kernel: kernel.lds kernel.o $(OBJS)
 	ld -Tkernel.lds kernel.o -o kernel $(OBJS)
@@ -15,4 +15,4 @@ loader.o: loader.s kernel
 	gcc -m32 loader.s -c -o loader.o
 
 %.o: %.c
-	clang $< -o $@ -c -ffreestanding -O3 -Wall
+	clang $< -o $@ -c -ffreestanding -O3 -Wall --target=x86_64-unknown -mcmodel=large -mno-mmx -mno-sse

gdt.c

@@ -0,0 +1,89 @@
+#include <stdint.h>
+#include "gdt.h"
+
+extern void stack;
+
+struct tss {
+	uint32_t _pad;
+	uint64_t rsp[3];
+	uint64_t _pad2;
+	uint64_t ist_rsp[7];
+	uint32_t _pad3[3];
+} __attribute__((packed)) tss = {
+	.rsp[0] = &stack,
+};
+
+_Static_assert(sizeof tss == 0x68, "meh");
+
+struct gdt_entry {
+	uint16_t limit_lo;
+	uint16_t base_lo;
+	uint8_t base_mid;
+	uint8_t flags_a;
+	uint8_t flags_b;
+	uint8_t base_hi;
+} gdt[] = {
+	// 0
+	{ 0 },
+	// 8: kernel code
+	{ 0, 0, 0, 0x9b, 0xa0, 0 },
+	// 0x10: user code 32-bit
+	{ 0xffff, 0, 0, 0xfb, 0xcf, 0 },
+	// 0x18: user data
+	{ 0xffff, 0, 0, 0xf3, 0xcf, 0 },
+	// 0x20: user code 64-bit
+	{ 0, 0, 0, 0xfb, 0xa0, 0 },
+	// 0x28: TSS
+	{ sizeof tss - 1, 0, 0, 0x89, 0, 0 },
+	{ 0, 0, 0, 0, 0, 0 },
+};
+
+struct idt_entry {
+	uint16_t addr_lo;
+	uint16_t segment;
+	uint8_t ist;
+	uint8_t flags;
+	uint16_t addr_mid;
+	uint32_t addr_hi;
+	uint32_t _pad;
+} idt[256] = {
+	{0},
+};
+
+void init_gdt() {
+	uint64_t tss_addr = (uint64_t)&tss;
+	gdt[5].base_lo = tss_addr;
+	gdt[5].base_mid = tss_addr >> 16;
+	gdt[5].base_hi = tss_addr >> 24;
+	gdt[6].limit_lo = tss_addr >> 32;
+	gdt[6].base_lo = tss_addr >> 48;
+	struct gdtr {
+		uint16_t _pad[3];
+		uint16_t limit;
+		void *addr;
+	} gdtr = {
+		{0, 0, 0}, sizeof gdt - 1, &gdt,
+	};
+	struct idtr {
+		uint16_t _pad[3];
+		uint16_t limit;
+		void *addr;
+	} idtr = {
+		{0, 0, 0}, sizeof idt - 1, &idt,
+	};
+	__asm__ volatile (
+		"lgdt (%0)"
+		:
+		: "r"(&gdtr.limit)
+	);
+	__asm__ volatile (
+		"lidt (%0)"
+		:
+		: "r"(&idtr.limit)
+	);
+	__asm__ volatile (
+		"ltr %0"
+		:
+		: "r"((uint16_t)0x28)
+	);
+}

gdt.h

@@ -0,0 +1 @@
+void init_gdt();

kernel.s

@@ -20,4 +20,5 @@ hlt
 .section .bss
 
 .skip 0x1000
+.global stack
 stack:

main.c

@@ -1,8 +1,30 @@
 #include <stdint.h>
+#include "gdt.h"
+#include "page.h"
 char hello[] = "Hello, C world!";
 
+__asm__(
+	".text\n"
+	"go_user:\n"
+	"pushq $0x1b\n"
+	"pushq $0\n"
+	"pushq $0x2\n"
+	"pushq $0x23\n"
+	"pushq %rdi\n"
+	"iretq\n"
+);
+
+_Noreturn void go_user(void *);
+
 void main() {
+	init_gdt();
+	init_pg();
+	map_page(0x31337000, phys_alloc(), 7);
+	uint8_t *upage = (void *)0x31337000ull;
+	upage[0] = 0xeb;
+	upage[1] = 0xfe;
+	go_user(upage);
 	for (int i = 0; i < sizeof hello; i++) {
-		*(uint16_t *)(0xffff8000000b8000 + i * 2) = hello[i] | 0x0f00;
+		*(uint16_t *)(0x31337000 + i * 2) = hello[i] | 0x0f00;
 	}
 }

page.c

@@ -0,0 +1,43 @@
+#include "page.h"
+
+extern void kbss_end;
+uint64_t phys_next = (uint64_t)(&kbss_end - 0xffff800000000000ull);
+
+uint64_t phys_alloc() {
+	if (phys_next & 0xfff) {
+		phys_next |= 0xfff;
+		phys_next++;
+	}
+	uint64_t res = phys_next;
+	phys_next += 0x1000;
+	return res;
+}
+
+void map_page(uint64_t virt, uint64_t phys, int flags) {
+	uint64_t p_ptl4 = read_cr3() & ~0xfffull;
+	uint64_t *v_ptl4 = P2V(p_ptl4);
+	int idx1 = virt >> 12 & 0x1ff;
+	int idx2 = virt >> 21 & 0x1ff;
+	int idx3 = virt >> 30 & 0x1ff;
+	int idx4 = virt >> 39 & 0x1ff;
+	if (!v_ptl4[idx4])
+		v_ptl4[idx4] = phys_alloc() | 7;
+	uint64_t p_ptl3 = v_ptl4[idx4] & ~0xfffull;
+	uint64_t *v_ptl3 = P2V(p_ptl3);
+	if (!v_ptl3[idx3])
+		v_ptl3[idx3] = phys_alloc() | 7;
+	uint64_t p_ptl2 = v_ptl3[idx3] & ~0xfffull;
+	uint64_t *v_ptl2 = P2V(p_ptl2);
+	if (!v_ptl2[idx2])
+		v_ptl2[idx2] = phys_alloc() | 7;
+	uint64_t p_ptl1 = v_ptl2[idx2] & ~0xfffull;
+	uint64_t *v_ptl1 = P2V(p_ptl1);
+	v_ptl1[idx1] = phys | flags;
+}
+
+void init_pg() {
+	uint64_t p_ptl4 = read_cr3() & ~0xfffull;
+	uint64_t *v_ptl4 = P2V(p_ptl4);
+	v_ptl4[0] = 0;
+	write_cr3(read_cr3());
+}

page.h

@@ -0,0 +1,27 @@
+#include <stdint.h>
+
+static inline void *P2V(uint64_t p) {
+	return (void *)(0xffff800000000000ull + p);
+}
+
+static inline uint64_t read_cr3() {
+	uint64_t res;
+	__asm__ volatile(
+		"movq %%cr3, %0"
+		: "=r"(res)
+		:
+	);
+	return res;
+}
+
+static inline void write_cr3(uint64_t val) {
+	__asm__ volatile(
+		"movq %0, %%cr3"
+		:
+		: "r"(val)
+	);
+}
+
+uint64_t phys_alloc();
+void init_pg();
+void map_page(uint64_t virt, uint64_t phys, int flags);