Interrupt Dispatch and Handling (for first common vectors)

GDT init (load + flush)

.gitignore

@@ -4,3 +4,6 @@ pepperk
 iso_root
 *.o
 *.iso
+*.gch
+*/*.gch
+*/*/*.gch

Makefile

@@ -1,7 +1,8 @@
 build:
 	rm -f *.o
-	x86_64-elf-gcc -g -c -I src src/io/serial.c src/io/term.c src/io/printf.c src/kmain.c -Wall -Wextra -std=gnu99 -nostdlib -ffreestanding -fno-stack-protector -fno-stack-check -fno-PIC -ffunction-sections -fdata-sections -mcmodel=kernel
+	x86_64-elf-gcc -g -c -I src src/idt/idt.c src/mem/utils.c src/mem/gdt.c src/io/serial.c src/io/term.c src/io/printf.c src/kmain.c -Wall -Wextra -std=gnu99 -nostdlib -ffreestanding -fno-stack-protector -fno-stack-check -fno-PIC -ffunction-sections -fdata-sections -mcmodel=kernel
 	objcopy -O elf64-x86-64 -B i386 -I binary zap-light16.psf zap-light16.o
+	nasm -f elf64 src/idt/idt.S -o idt_stub.o
 	x86_64-elf-ld -o pepperk -T linker.ld *.o
 
 limine/limine:
@@ -27,7 +28,7 @@ build-iso: limine/limine build
 	./limine/limine bios-install pepper.iso
 
 debug:
-	qemu-system-x86_64 -drive file=pepper.iso -s -S &
+	qemu-system-x86_64 -drive file=pepper.iso -s -S -d int -no-reboot &
 	gdb pepperk --command=debug.gdb
 
 run: build-iso

debug.gdb

@@ -1 +1,2 @@
 target remote localhost:1234
+set disassembly-flavor intel

src/idt/idt.S

@@ -0,0 +1,236 @@
+; Assembly stub for the IDT
+
+bits 64
+
+extern interrupt_dispatch
+
+global interrupt_stub
+global vector_0_handler
+global vector_1_handler
+global vector_2_handler
+global vector_3_handler
+global vector_4_handler
+global vector_5_handler
+global vector_6_handler
+global vector_7_handler
+global vector_8_handler
+global vector_9_handler
+global vector_10_handler
+global vector_11_handler
+global vector_12_handler
+global vector_13_handler
+global vector_14_handler
+global vector_15_handler
+global vector_16_handler
+global vector_17_handler
+global vector_18_handler
+global vector_19_handler
+global vector_20_handler
+global vector_21_handler
+
+interrupt_stub:
+    ; We'll push all general-purpose registers to the stack,
+    ; so they're intact and don't bother the code that was
+    ; executed when the interrupt happened.
+    ; (except rsp because it will already be saved in the iret frame)
+    
+    push rax
+    push rbx
+    push rcx
+    push rdx
+    push rsi 
+    push rdi
+    push rsp
+    push rbp
+    push r8
+    push r9
+    push r10
+    push r11
+    push r12
+    push r13
+    push r14
+    push r15
+
+    ; Put stack pointer as first argument of our function
+    mov rdi, rsp
+    call interrupt_dispatch
+    ; What the function returns (new stack pointer) is saved in rbp
+    mov rsp, rax
+
+    pop r15
+    pop r14
+    pop r13
+    pop r12
+    pop r11
+    pop r10
+    pop r9
+    pop r8
+    pop rbp
+    pop rsp
+    pop rdi
+    pop rsi
+    pop rdx
+    pop rcx
+    pop rbx
+    pop rax
+
+    ; Removing the error code and vector number so stack doesn't
+    ; get corrupted
+    add rsp, 16
+    
+    ; Restore ss, rsp, rflags, cs, rip of code that was executing
+    ; before the interrupt
+    iret
+
+; Vector handlers will be 16-byte aligned so that we can loop over them
+; like <vector_no> * 16 to get each one's address
+
+; Divide Error
+align 16
+vector_0_handler:
+    ; error code (nothing, so we push a dummy 0 quadword, 64bits/8bytes long)
+    push qword 0
+    ; vector number (so our interrupt stub knows which one it is)
+    push qword 0
+    jmp interrupt_stub
+
+; Debug Exception
+align 16
+vector_1_handler:
+    push qword 0
+    push qword 1
+    jmp interrupt_stub
+
+; NMI
+align 16
+vector_2_handler:
+    push qword 0
+    push qword 2
+    jmp interrupt_stub
+
+; Breakpoint
+align 16
+vector_3_handler:
+    push qword 0
+    push qword 3
+    jmp interrupt_stub
+
+; Overflow
+align 16
+vector_4_handler:
+    push qword 0
+    push qword 4
+    jmp interrupt_stub
+
+; BOUND Range exceeded
+align 16
+vector_5_handler:
+    push qword 0
+    push qword 5
+    jmp interrupt_stub
+
+; Invalid Opcode
+align 16
+vector_6_handler:
+    push qword 0
+    push qword 6
+    jmp interrupt_stub
+
+; Device Not Available
+align 16
+vector_7_handler:
+    push qword 0
+    push qword 7
+    jmp interrupt_stub
+
+; Double Fault
+align 16
+vector_8_handler:
+    ; No error code, we only push vector number
+    push qword 1
+    jmp interrupt_stub
+
+; Coprocessor Segment Overrun
+align 16
+vector_9_handler:
+    push qword 9
+    jmp interrupt_stub
+
+; Invalid TSS
+align 16
+vector_10_handler:
+    push qword 10
+    jmp interrupt_stub
+
+; Segment Not Present
+align 16
+vector_11_handler:
+    push qword 11
+    jmp interrupt_stub
+
+; Stack-Segment Fault
+align 16
+vector_12_handler:
+    push qword 12
+    jmp interrupt_stub
+
+; General Protection
+align 16
+vector_13_handler:
+    push qword 13
+    jmp interrupt_stub
+
+; Page Fault
+align 16
+vector_14_handler:
+    push qword 14
+    jmp interrupt_stub
+
+; Intel reserved
+align 16
+vector_15_handler:
+    push qword 0
+    push qword 15
+    jmp interrupt_stub
+
+; x87 FPU Floating-Point Error
+align 16
+vector_16_handler:
+    push qword 0
+    push qword 16
+    jmp interrupt_stub
+
+; Alignment Check
+align 16
+vector_17_handler:
+    push qword 17
+    jmp interrupt_stub
+
+; Machine Check
+align 16
+vector_18_handler:
+    push qword 0
+    push qword 18
+    jmp interrupt_stub
+
+; SIMD Floating-Point Exception
+align 16
+vector_19_handler:
+    push qword 0
+    push qword 19
+    jmp interrupt_stub
+
+; Virtualization Exception
+align 16
+vector_20_handler:
+    push qword 0
+    push qword 20
+    jmp interrupt_stub
+
+; Control Protection Exception
+align 16
+vector_21_handler:
+    push qword 21
+    jmp interrupt_stub
+
+; The others are reserved (22->31) or external (32->255) interrupts

src/idt/idt.c

@@ -0,0 +1,128 @@
+#include "idt.h"
+#include <stdint.h>
+#include <stddef.h>
+#include "../io/serial.h"
+
+struct interrupt_descriptor idt[256];
+struct idtr idt_reg;
+
+// Address to our first interrupt handler
+extern char vector_0_handler[];
+
+void idt_set_entry(uint8_t vector, void* handler, uint8_t dpl)
+{
+    uint64_t handler_addr = (uint64_t)handler;
+
+    struct interrupt_descriptor* entry = &idt[vector];
+    // Address is split in three parts so we right-shift progressively to get it all
+    entry->address_low = handler_addr & 0xFFFF;
+    entry->address_mid = (handler_addr >> 16) & 0xFFFF;
+    entry->address_high = handler_addr >> 32;
+
+    // Kernel code selector (as set in GDT)
+    entry->selector = 0x8;
+    // Interrupt gate, present, DPL (having: max DPL = 3)
+    entry->flags = 0b1110 | ((dpl & 0b11) << 5) | (1 << 7);
+    // We won't use IST for now
+    entry->ist = 0;
+}
+
+void idt_load(void* idt_addr)
+{
+    // "limit" = "size" = Size of the IDT - 1 byte = (16*256)-1 = 0xFFF
+    idt_reg.limit = 0xFFF;
+    idt_reg.base = (uint64_t)idt_addr;
+    asm volatile("lidt %0" :: "m"(idt_reg));
+}
+
+void idt_init()
+{
+    // We set 256 entries, but we have only the first few stubs.
+    // Undefined behavior?
+    for (size_t i=0; i<256; i++)
+    {
+        // Each vector handler is 16-byte aligned, so <vector_no>*16 = address of that handler
+        idt_set_entry(i, vector_0_handler + (i*16), 0);
+    }
+    idt_load(&idt);
+    serial_kputs("kernel: idt: Initialized IDT!\n");
+}
+
+struct cpu_status_t* interrupt_dispatch(struct cpu_status_t* context)
+{
+    switch(context->vector_number)
+    {
+        case 0:
+            serial_kputs("kernel: idt: Divide Error!\n");
+            break;
+        case 1:
+            serial_kputs("kernel: idt: Debug Exception!\n");
+            break;
+        case 2:
+            serial_kputs("kernel: idt: NMI Interrupt!\n");
+            break;
+        case 3:
+            serial_kputs("kernel: idt: Breakpoint Interrupt!\n");
+            break;
+        case 4:
+            serial_kputs("kernel: idt: Overflow Trap!\n");
+            break;
+        case 5:
+            serial_kputs("kernel: idt: BOUND Range Exceeded!\n");
+            break;
+        case 6:
+            serial_kputs("kernel: idt: Invalid Opcode!\n");
+            break;
+        case 7:
+            serial_kputs("kernel: idt: Device Not Available!\n");
+            break;
+        case 8:
+            serial_kputs("kernel: idt: Double Fault!\n");
+            break;
+        case 9:
+            serial_kputs("kernel: idt: Coprocessor Segment Overrun!\n");
+            break;
+        case 10:
+            serial_kputs("kernel: idt: Invalid TSS!\n");
+            break;
+        case 11:
+            serial_kputs("kernel: idt: Segment Not Present!\n");
+            break;
+        case 12:
+            serial_kputs("kernel: idt: Stack-Segment Fault!\n");
+            break;
+        case 13:
+            serial_kputs("kernel: idt: General Protection Fault!\n");
+            break;
+        case 14:
+            serial_kputs("kernel: idt: Page Fault!\n");
+            break;
+        case 15:
+            serial_kputs("kernel: idt: Intel Reserved Interrupt! (Achievement unlocked: How Did We Get Here?)\n");
+            break;
+        case 16:
+            serial_kputs("kernel: idt: x87 Floating-Point Error!\n");
+            break;
+        case 17:
+            serial_kputs("kernel: idt: Alignment Check Fault!\n");
+            break;
+        case 18:
+            serial_kputs("kernel: idt: Machine Check!\n");
+            break;
+        case 19:
+            serial_kputs("kernel: idt: SIMD Floating-Point Exception!\n");
+            break;
+        case 20:
+            serial_kputs("kernel: idt: Virtualization Exception!\n");
+            break;
+        case 21:
+            serial_kputs("kernel: idt: Control Protection Exception!\n");
+            break;
+
+        default:
+            serial_kputs("kernel: idt: Unexpected interrupt\n");
+            break;
+    }
+
+    return context;
+}

src/idt/idt.h

@@ -0,0 +1,57 @@
+#ifndef IDT_H
+#define IDT_H
+
+#include <stdint.h>
+
+void idt_init();
+
+struct interrupt_descriptor
+{
+    uint16_t address_low;
+    uint16_t selector;
+    uint8_t ist;
+    uint8_t flags;
+    uint16_t address_mid;
+    uint32_t address_high;
+    uint32_t reserved;
+} __attribute__((packed));
+
+struct idtr 
+{
+    uint16_t limit;
+    uint64_t base;
+} __attribute__((packed));
+
+// All general-purpose registers (except rsp) as stored on the stack,
+// plus the values we pushed (vector number, error code) and the iret frame
+// In reverse order because the stack grows downwards.
+struct cpu_status_t
+{
+    uint64_t r15;
+    uint64_t r14;
+    uint64_t r13;
+    uint64_t r12;
+    uint64_t r11;
+    uint64_t r10;
+    uint64_t r9;
+    uint64_t r8;
+    uint64_t rbp;
+    uint64_t rsp;
+    uint64_t rdi;
+    uint64_t rsi;
+    uint64_t rdx;
+    uint64_t rcx;
+    uint64_t rbx;
+    uint64_t rax;
+
+    uint64_t vector_number;
+    uint64_t error_code;
+
+    uint64_t iret_rip;
+    uint64_t iret_cs;
+    uint64_t iret_flags;
+    uint64_t iret_rsp;
+    uint64_t iret_ss;
+};
+
+#endif

src/io/serial.c

@@ -1,4 +1,5 @@
 #include "../kernel.h"
+#include "serial.h"
 
 void outb(int port, unsigned char data)
 {
@@ -34,6 +35,8 @@ int serial_init()
 
     // Set normal operation mode
     outb(PORT + 4, 0x0F);
+
+    serial_kputs("\n\nkernel: serial: Serial initialization OK!\n");
     return 0;
 }
 

src/kmain.c

@@ -4,6 +4,9 @@
 #include "io/term.h"
 #include "io/printf.h"
 #include "io/serial.h"
+#include "mem/gdt.h"
+#include "mem/utils.h"
+#include "idt/idt.h"
 
 // Limine version used
 __attribute__((used, section(".limine_requests")))
@@ -24,74 +27,6 @@ static volatile LIMINE_REQUESTS_END_MARKER;
 
 struct limine_framebuffer* framebuffer;
 
-// We won't be linked to standard library, but still need the basic mem* functions
-// so everything goes allright with the compiler
-
-// We use the "restrict" keyword on pointers so that the compiler knows it can
-// do more optimization on them (and as it's a much used function, it's good to
-// be able to do that)
-void* memcpy(void* restrict dest, const void* restrict src, size_t n)
-{
-	uint8_t* restrict pdest = (uint8_t* restrict)dest;
-	const uint8_t* restrict psrc = (const uint8_t* restrict)src;
-
-	for (size_t i=0; i<n; i++)
-	{
-		pdest[i] = psrc[i];
-	}
-
-	return dest;
-}
-
-void* memset(void* s, int c, size_t n)
-{
-	uint8_t* p = (uint8_t*)s;
-
-	for (size_t i=0; i<n; i++)
-	{
-		p[i] = (uint8_t)c;
-	}
-
-	return s;
-}
-
-void* memmove(void *dest, const void* src, size_t n)
-{
-	uint8_t* pdest = (uint8_t*)dest;
-	const uint8_t* psrc = (uint8_t*)src;
-
-	if (src > dest)
-	{
-		for (size_t i=0; i<n; i++)
-		{
-			pdest[i] = psrc[i];
-		}
-	} else if (src < dest) 
-	{
-		for (size_t i=n; i>0; i--)
-		{
-			pdest[i-1] = psrc[i-1];
-		}
-	}
-	return dest;	
-}
-
-int memcmp(const void* s1, const void* s2, size_t n)
-{
-	const uint8_t* p1 = (const uint8_t*)s1;
-	const uint8_t* p2 = (const uint8_t*)s2;
-
-	for (size_t i=0; i<n; i++)
-	{
-		if (p1[i] != p2[i])
-		{
-			return p1[i] < p2[i] ? -1 : 1;
-		}
-	}
-
-	return 0;
-}
-
 // Panic 
 static void hcf()
 {
@@ -101,6 +36,20 @@ static void hcf()
 	}
 }
 
+static inline void trigger_div0(void)
+{
+    asm volatile (
+        "mov $1, %%rax\n"
+        "xor %%rdx, %%rdx\n"
+        "xor %%rcx, %%rcx\n"  // divisor = 0
+        "idiv %%rcx\n"
+        :
+        :
+        : "rax", "rcx", "rdx"
+    );
+}
+
+
 // This is our entry point
 void kmain()
 {
@@ -114,10 +63,12 @@ void kmain()
 
 	if (serial_init()) kputs("kernel: serial: error: Cannot init serial communication!");
 
-	serial_kputs("\n\nkernel: serial: Hello, world from serial!");
+	gdt_init();
+	idt_init();
 
 	// Draw something
 	printf("%s, %s!", "Hello", "world");
 
+	trigger_div0();
 	hcf();
 }

src/mem/gdt.c

@@ -0,0 +1,82 @@
+#include "gdt.h"
+#include <stdint.h>
+#include "../io/serial.h"
+
+// Descriptors are 8-byte wide (64bits)
+// So the selectors will be (in bytes): 0x0, 0x8, 0x10, 0x18, etc..
+uint64_t gdt_entries[NUM_GDT_ENTRIES];
+struct GDTR gdtr;
+
+static void gdt_load()
+{
+    asm("lgdt %0" : : "m"(gdtr));
+}
+
+static void gdt_flush()
+{
+    // Here, 0x8 is the kernel code selector
+    // and 0x10 is the kernel data selector
+    asm volatile (
+        "mov $0x10, %%ax \n" // Reload segments with kernel data selector
+        "mov %%ax, %%ds \n"
+        "mov %%ax, %%es \n"
+        "mov %%ax, %%fs \n"
+        "mov %%ax, %%gs \n"
+        "mov %%ax, %%ss \n"
+
+        "pushq $0x8      \n"   // CS reload
+        "lea 1f(%%rip), %%rax \n"
+        "push %%rax     \n"
+        "lretq          \n"
+        "1:             \n" // Execution continues here after CS reload
+        :
+        :
+        : "rax", "memory"
+    );
+}
+
+void gdt_init()
+{
+    // Null descriptor (required)
+    gdt_entries[0] = 0;
+
+    // Kernel code segment
+    uint64_t kernel_code = 0;
+    kernel_code |= 0b1101 << 8; // Selector type: accessed, read-enable, no conforming
+    kernel_code |= 1 << 12; // not a system descriptor
+    kernel_code |= 0 << 13; // DPL field = 0
+    kernel_code |= 1 << 15; // Present
+    kernel_code |= 1 << 21; // Long mode
+
+    // Left shift 32 bits so we place our stuff in the upper 32 bits of the descriptor.
+    // The lower 32 bits contain limit and part of base and therefore are ignored in Long Mode
+    // (because we'll use paging; segmentation is used only for legacy)
+    gdt_entries[1] = kernel_code << 32;
+
+    uint64_t kernel_data = 0;
+    kernel_data |= 0b0011 << 8;
+    kernel_data |= 1 << 12;
+    kernel_data |= 0 << 13;
+    kernel_data |= 1 << 15;
+    kernel_data |= 1 << 21;
+
+    gdt_entries[2] = kernel_data << 32;
+
+    // We re-use the kernel descriptors here, and just update their DPL fields
+    // (Descriptor privilege level) from ring 0 -> to ring 3 (userspace)
+    uint64_t user_code = kernel_code | (3 << 13);
+    gdt_entries[3] = user_code;
+
+    uint64_t user_data = kernel_data | (3 << 13);
+    gdt_entries[4] = user_data;
+
+    // The -1 subtraction is some wizardry explained in the OSDev wiki -> GDT
+    gdtr.limit = NUM_GDT_ENTRIES * sizeof(uint64_t) - 1;
+    gdtr.address = (uint64_t)gdt_entries;
+
+    // Load the GDT we created, flush the old one
+    gdt_load();
+    gdt_flush();
+
+    serial_kputs("kernel: gdt: Initialized GDT!\n");
+}

src/mem/gdt.h

@@ -0,0 +1,26 @@
+#ifndef GDT_H
+#define GDT_H
+
+#include <stdint.h>
+
+// We're using the GDT for segmentation, but as we want to target Long Mode,
+// we'll only use this as a requirement for paging, not more.
+// This means base 0 and no limit (whole address space)
+
+#define NUM_GDT_ENTRIES 5
+
+#define NULL_SELECTOR 0x00
+#define KERNEL_CODE_SEGMENT 0x08
+#define KERNEL_DATA_SEGMENT 0x10
+#define USER_CODE_SEGMENT 0x18
+#define USER_DATA_SEGMENT 0x20
+
+struct GDTR 
+{
+    uint16_t limit;
+    uint64_t address;
+} __attribute__((packed));
+
+void gdt_init();
+
+#endif

src/mem/utils.c

@@ -0,0 +1,70 @@
+#include <stddef.h>
+#include <stdint.h>
+
+// We won't be linked to standard library, but still need the basic mem* functions
+// so everything goes allright with the compiler
+
+// We use the "restrict" keyword on pointers so that the compiler knows it can
+// do more optimization on them (and as it's a much used function, it's good to
+// be able to do that)
+void* memcpy(void* restrict dest, const void* restrict src, size_t n)
+{
+	uint8_t* restrict pdest = (uint8_t* restrict)dest;
+	const uint8_t* restrict psrc = (const uint8_t* restrict)src;
+
+	for (size_t i=0; i<n; i++)
+	{
+		pdest[i] = psrc[i];
+	}
+
+	return dest;
+}
+
+void* memset(void* s, int c, size_t n)
+{
+	uint8_t* p = (uint8_t*)s;
+
+	for (size_t i=0; i<n; i++)
+	{
+		p[i] = (uint8_t)c;
+	}
+
+	return s;
+}
+
+void* memmove(void *dest, const void* src, size_t n)
+{
+	uint8_t* pdest = (uint8_t*)dest;
+	const uint8_t* psrc = (uint8_t*)src;
+
+	if (src > dest)
+	{
+		for (size_t i=0; i<n; i++)
+		{
+			pdest[i] = psrc[i];
+		}
+	} else if (src < dest) 
+	{
+		for (size_t i=n; i>0; i--)
+		{
+			pdest[i-1] = psrc[i-1];
+		}
+	}
+	return dest;	
+}
+
+int memcmp(const void* s1, const void* s2, size_t n)
+{
+	const uint8_t* p1 = (const uint8_t*)s1;
+	const uint8_t* p2 = (const uint8_t*)s2;
+
+	for (size_t i=0; i<n; i++)
+	{
+		if (p1[i] != p2[i])
+		{
+			return p1[i] < p2[i] ? -1 : 1;
+		}
+	}
+
+	return 0;
+}

src/mem/utils.h

@@ -0,0 +1,11 @@
+#ifndef MEM_UTILS_H
+#define MEM_UTILS_H
+
+#include <stddef.h>
+
+void* memcpy(void* restrict dest, const void* restrict src, size_t n);
+void* memset(void* s, int c, size_t n);
+void* memmove(void *dest, const void* src, size_t n);
+int memcmp(const void* s1, const void* s2, size_t n);
+
+#endif