Add simple kernel logging and improve error messages

meson.build

@@ -74,6 +74,7 @@ kernel_sources = files([
   'src/kernel/idt.c',
   'src/kernel/kernel.c',
   'src/kernel/keyboard.c',
+  'src/kernel/log.c',
   'src/kernel/memory.c',
   'src/kernel/panic.c',
   'src/kernel/path.c',

src/kernel/idt.c

@@ -38,3 +38,7 @@ void idt_set_entry(int vector, void (*handler)(struct interrupt_frame *), uint8_
   idt[vector].offset_high = (addr >> 32) & 0xFFFFFFFF;
   idt[vector].zero = 0;
 }
+
+void idt_set_entry_ec(int vector, void (*handler)(struct interrupt_frame *, uint64_t error), uint8_t flags) {
+  idt_set_entry(vector, (void *)handler, flags);
+}

src/kernel/idt.h

@@ -13,3 +13,5 @@ struct interrupt_frame {
 void idt_init();
 
 void idt_set_entry(int vector, void (*handler)(struct interrupt_frame *), uint8_t flags);
+
+void idt_set_entry_ec(int vector, void (*handler)(struct interrupt_frame *, uint64_t error), uint8_t flags);

src/kernel/kernel.c

@@ -2,11 +2,13 @@
 #include "src/kernel/gdt.h"
 #include "src/kernel/idt.h"
 #include "src/kernel/keyboard.h"
+#include "src/kernel/log.h"
 #include "src/kernel/panic.h"
 #include "src/kernel/path.h"
 #include "src/kernel/pic.h"
 #include "src/kernel/pipe.h"
 #include "src/kernel/process.h"
+#include "src/kernel/stream.h"
 #include "src/kernel/syscall.h"
 #include "src/kernel/timer.h"
 #include "src/kernel/tss.h"
@@ -22,8 +24,14 @@ __attribute__((interrupt)) void isr_divide_by_zero(__attribute__((unused)) struc
     ;
 }
 
-__attribute__((interrupt)) void isr_page_fault(__attribute__((unused)) struct interrupt_frame *frame) {
+__attribute__((interrupt)) void isr_page_fault(__attribute__((unused)) struct interrupt_frame *frame, uint64_t error_code) {
-  vga_set_string(VGA_HEIGHT - 1, 0, "EXCEPTION: page fault", 0x4F);
+  uint64_t cr2;
+  __asm__ volatile("mov %%cr2, %0" : "=r"(cr2));
+
+  char msg[80];
+  string_format("EXCEPTION: page fault; addr=%x err=%x", 80, msg, cr2, error_code);
+
+  vga_set_string(VGA_HEIGHT - 1, 0, msg, 0x4F);
   while (1)
     ;
 }
@@ -40,11 +48,14 @@ __attribute__((interrupt)) void isr_ata_primary(__attribute__((unused)) struct i
 }
 
 void kernel_main() {
+  stream_t *vga = vga_init();
+  log_init(vga);
+
   pic_init();
   idt_init();
   outb(0x21, inb(0x21) | 0x01); // mask out timer interrupt
   idt_set_entry(0, isr_divide_by_zero, 0x8E);
-  idt_set_entry(0x0E, isr_page_fault, 0x8E);
+  idt_set_entry_ec(0x0E, isr_page_fault, 0x8E);
   idt_set_entry(0x0D, isr_general_violation, 0x8E);
   idt_set_entry(46, isr_ata_primary, 0x8E);
 
@@ -59,8 +70,7 @@ void kernel_main() {
   kernel->user_stack = kernel->user_rsp = (uint8_t *)memory_allocate(PAGE_SIZE) + PAGE_SIZE;
   kernel->cwd = memory_allocate(sizeof(path_t));
   kernel->fds[STDIN] = keyboard_init();
-  kernel->fds[STDOUT] = vga_init();
+  kernel->fds[STDOUT] = kernel->fds[STDERR] = vga;
-  kernel->fds[STDERR] = kernel->fds[STDOUT];
   kernel->free_fd = STDERR + 1;
   kernel->code = EXIT_CODE_OK;
 

src/kernel/log.c

@@ -0,0 +1,8 @@
+#include "src/kernel/log.h"
+#include "src/kernel/stream.h"
+
+stream_t *kernel_log;
+
+void log_init(stream_t *log) {
+  kernel_log = log;
+}

src/kernel/log.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "src/kernel/stream.h"
+#include "src/lib/memory.h"
+#include "src/lib/string.h"
+
+extern stream_t *kernel_log;
+
+#define LOG(fmt, ...)                                                                                                                      \
+  do {                                                                                                                                     \
+    uint64_t _size = string_length(fmt) * 2;                                                                                               \
+    char *_string = memory_allocate(_size);                                                                                                \
+    _size = string_format(fmt, _size, _string, ##__VA_ARGS__);                                                                             \
+    kernel_log->write(kernel_log, _string, _size);                                                                                         \
+    memory_free(_string);                                                                                                                  \
+  } while (0)
+
+#define TRACE(fmt, ...)
+
+void log_init(stream_t *log);

src/kernel/memory.c

@@ -1,4 +1,5 @@
 #include "src/kernel/memory.h"
+#include "src/kernel/log.h"
 #include "src/kernel/panic.h"
 #include "src/lib/layout.h"
 #include "src/lib/memory.h"
@@ -66,7 +67,10 @@ void memory_page_map(uint64_t *pml4, void *virt, void *phys, uint64_t flags) {
   const uint64_t pd_index = (ivirt >> 21) & 0x1FF;
   const uint64_t pt_index = (ivirt >> 12) & 0x1FF;
 
+  TRACE("memory_page_map: Mapping physical %x to virtual %x / [%u, %u, %u, %u]...\n", phys, virt, pml4_index, pdpt_index, pd_index, pt_index);
+
   if (!(pml4[pml4_index] & PAGE_PRESENT)) {
+    TRACE("memory_page_map: PML4 entry %u does not exist, creating...\n", pml4_index);
     uint64_t *pdpt = memory_page_allocate();
     memory_set(0, PAGE_SIZE, PHYS_TO_VIRT(pdpt));
     pml4[pml4_index] = (uint64_t)pdpt | PAGE_PRESENT | PAGE_WRITABLE | PAGE_USER;
@@ -74,21 +78,32 @@ void memory_page_map(uint64_t *pml4, void *virt, void *phys, uint64_t flags) {
 
   uint64_t *pdpt = PHYS_TO_VIRT(pml4[pml4_index] & ~(uint64_t)0xFFF);
   if (!(pdpt[pdpt_index] & PAGE_PRESENT)) {
+    TRACE("memory_page_map: PDPT entry %u does not exist, creating...\n", pdpt_index);
     uint64_t *pd = memory_page_allocate();
     memory_set(0, PAGE_SIZE, PHYS_TO_VIRT(pd));
     pdpt[pdpt_index] = (uint64_t)pd | PAGE_PRESENT | PAGE_WRITABLE | PAGE_USER;
   }
 
   uint64_t *pd = PHYS_TO_VIRT(pdpt[pdpt_index] & ~(uint64_t)0xFFF);
-  ASSERT(!(pd[pd_index] & 0x80), "memory_page_map: huge page in PD");
+  ASSERT(!(pd[pd_index] & 0x80), "memory_page_map: Huge page in PD.");
   if (!(pd[pd_index] & PAGE_PRESENT)) {
+    TRACE("memory_page_map: PD entry %u does not exist, creating...\n", pd_index);
     uint64_t *pt = memory_page_allocate();
     memory_set(0, PAGE_SIZE, PHYS_TO_VIRT(pt));
     pd[pd_index] = (uint64_t)pt | PAGE_PRESENT | PAGE_WRITABLE | PAGE_USER;
   }
 
   uint64_t *pt = PHYS_TO_VIRT(pd[pd_index] & ~(uint64_t)0xFFF);
+
+  ASSERT(!(pt[pt_index] & PAGE_PRESENT), "memory_page_map: Page already mapped.")
+
+  TRACE("memory_page_map: PT entry %u does not exist, creating...\n", pt_index);
+
   pt[pt_index] = (uint64_t)phys | flags | PAGE_PRESENT;
+
+  TRACE("memory_page_map: Created %x.\n", pt[pt_index]);
+
+  TRACE("memory_page_map: Done.\n");
 }
 
 void memory_page_unmap(uint64_t *pml4, void *virt) {