Added <errno.h> and made kernel use it

docs/errors.txt

@@ -0,0 +1,32 @@
+Error handling
+==============
+
+Functions that can fail must have a way of telling the caller that something
+went wrong and preferably what went wrong. The simplest and cleanest way of 
+indicating an error is a return code. Error codes are defined in the <errno.h>
+header alongside some helpfull macros.
+
+Error codes have identifiers like these: ENOMEM, ENOENT, EALIGN, ...
+They are defined as positive values, however all functions should return a
+negative integer on error, so it would look something like 'return -EFAULT;'.
+Also theres SUCCESS which is just 0. You can use it, but don't need to.
+
+If you are returning a pointer/address, the highest address is almost certainly
+unused, so returning '(void*)-EINVAL', should work just fine. This is quite an
+eyesore, so there are three macros for working with these "errno-in-pointer"s.
+IS_ERR(ptr) just returns 1 if the pointer is an errno. Otherwise 0.
+ERR_PTR(err) does that void* cast mentioned above so it would be ERR_PTR(-EINVAL).
+PTR_ERR(ptr) is the inverse of ERR_PTR(), as it converts a errno-in-pointer to
+an errno value. PTR_ERR(ERR_PTR(-EIO)) == -EIO
+
+
+Here are some usage examples:
+	int pag_init(void) {
+		if (...) return -ENOMEM; // Not enough memory
+		
+		void* paddr = pmm_alloc();
+		if (IS_ERR(paddr)) return PTR_ERR(paddr); // Pass the error down
+
+		return SUCCESS;
+	}
+

kernel/include/errno.h

@@ -0,0 +1,35 @@
+#ifndef _ERRNO_H
+#define _ERRNO_H
+
+#include <kernel.h>
+
+#define ERRNO_MAX 4095
+
+#define IS_ERR(_ptr) ((uintptr_t)(_ptr) >= (uintptr_t)(-ERRNO_MAX))
+
+#define ERR_PTR(_err) ((void*)(_err))
+#define PTR_ERR(_ptr) ((int)(intptr_t)(_ptr))
+
+// TODO: Add correct errno.h numbers
+enum {
+	SUCCESS = 0,
+	ENOMEM,		// Cannot allocate memory
+	EPERM,		// Operation not permitted
+	ENOENT,		// No entry (no such file or directory)
+	EIO,		// Input/Output error
+	ENXIO,		// No such device or address
+	EAGAIN,		// Resource temporarly busy
+	EACCES,		// Permission denied
+	EFAULT,		// Bad address
+	ENODEV,		// No such device
+	EINVAL,		// Invalid argument
+	EDOM,		// Numerical argument out of domain
+	ERANGE,		// Numerical result out of range
+	ENOSYS,		// Function not implemented
+	ENOTSUP,	// Not supported
+	EILLSEQ,	// Illegal byte sequence
+	EOVERFLOW,	// 
+	EALIGN,		// Not aligned
+};
+
+#endif

kernel/include/idt.h

@@ -32,6 +32,6 @@ struct idt_pointer {
 } __packed;
 
 int idt_init(void);
-void idt_set_gate(uint8_t i, void* handler, uint8_t flags);
+void idt_set_gate(uint8_t i, void* handler, uint8_t flags, uint8_t ist);
 
 #endif

kernel/include/paging.h

@@ -41,11 +41,11 @@ static inline bool pag_is_user_addr(void* vaddr) { return (uintptr_t)vaddr < 0x0
 // NOTE: All uint64_t* are VIRTUAL addresses
 int	  pag_init(void);
 uint64_t* pag_get_pte(uint64_t* pml4, void* vaddr);
-void	  pag_map(uint64_t* pml4, void* vaddr, void* paddr, uint64_t flags);
-void	  pag_map_region(uint64_t* pml4, void* vaddr, void* paddr, size_t count, uint64_t flags);
-void	  pag_unmap(uint64_t* pml4, void* vaddr);
-void	  pag_unmap_region(uint64_t* pml4, void* vaddr, size_t count);
-void	  pag_protect(uint64_t* pml4, void* vaddr, uint64_t flags);
+int	  pag_map(uint64_t* pml4, void* vaddr, void* paddr, uint64_t flags);
+int	  pag_map_region(uint64_t* pml4, void* vaddr, void* paddr, size_t count, uint64_t flags);
+int	  pag_unmap(uint64_t* pml4, void* vaddr);
+int	  pag_unmap_region(uint64_t* pml4, void* vaddr, size_t count);
+int	  pag_protect(uint64_t* pml4, void* vaddr, uint64_t flags);
 void*	  pag_get_phys(uint64_t* pml4, void* vaddr);
 void	  pag_set_pml4(uint64_t* pml4);
 uint64_t* pag_get_pml4(void);

kernel/include/pmm.h

@@ -5,6 +5,6 @@
 
 int pmm_init(void);
 void* pmm_alloc(void);
-void pmm_free(void*);
+int pmm_free(void*);
 
 #endif

kernel/include/serial.h

@@ -18,6 +18,7 @@ int  serial_rcvd(int dev);
 char serial_recv(int dev);
 void serial_write(int dev, char* buf, size_t len);
 void serial_puts(int dev, char* s);
+void serial_cls(int dev);
 
 int debugf(char* fmt, ...);
 int vdebugf(char* fmt, va_list args);

kernel/makefile

@@ -18,7 +18,7 @@ $(OUT): $(OBJS_C) $(OBJS_S)
 
 $(BIN)/%.c.o: $(SRC)/%.c $(SSP)
 	@mkdir -p $(dir $@)
-	$(CC) $(CCFLAGS) -DSTACK_CHK_GUARD=$(shell cat $(SSP)) -I$(INC) -c -o $@ $<
+	$(CC) $(CCFLAGS) -DSTACK_CHK_GUARD="$$(cat $(SSP))" -I$(INC) -c -o $@ $<
 
 $(BIN)/%.s.o: $(SRC)/%.s
 	@mkdir -p $(dir $@)

kernel/src/bootloader.c

@@ -1,14 +1,12 @@
 #include <bootloader.h>
 #include <kernel.h>
 #include <limine.h>
+#include <errno.h>
 
-/*
- * This defines our expected Limine version
- */
+// This defines our expected Limine version
 static volatile uint64_t lim_base_revision[] = LIMINE_BASE_REVISION(4);
 
-struct bootloader bootloader = { 0 };
-
+// Limine requests
 static struct limine_paging_mode_request lim_paging_req =
 	{ .id = LIMINE_PAGING_MODE_REQUEST_ID, .revision = 4,
 	  .mode = LIMINE_PAGING_MODE_X86_64_4LVL, };
@@ -28,6 +26,9 @@ static struct limine_framebuffer_request lim_fbuf_req =
 static struct limine_executable_file_request lim_exe_req =
 	{ .id = LIMINE_EXECUTABLE_FILE_REQUEST_ID, .revision = 4 };
 
+// Bootloader data struct
+struct bootloader bootloader = { 0 };
+
 int boot_init(void) {
 	if (LIMINE_BASE_REVISION_SUPPORTED(lim_base_revision) == false) panic("Unsupported Limine base revision.");
 
@@ -38,10 +39,7 @@ int boot_init(void) {
 	struct limine_framebuffer_response* lim_fbuf_res = lim_fbuf_req.response;
 	struct limine_executable_file_response* lim_exe_res = lim_exe_req.response;
 
-	if (lim_paging_res->mode != LIMINE_PAGING_MODE_X86_64_4LVL) {
-		debugf("[boot] Expected 4 level paging.\n");
-		return 1;
-	}
+	if (lim_paging_res->mode != LIMINE_PAGING_MODE_X86_64_4LVL) panic("Expected 4 level paging.");
 	bootloader.hhdm_offset = lim_hhdm_res->offset;
 	bootloader.kernel_phys_base = lim_kaddr_res->physical_base;
 	bootloader.kernel_virt_base = lim_kaddr_res->virtual_base;
@@ -58,6 +56,6 @@ int boot_init(void) {
 	bootloader.fb_entries = lim_fbuf_res->framebuffers;
 	bootloader.fb_entry_count = lim_fbuf_res->framebuffer_count;
 
-	return 0;
+	return SUCCESS;
 }
 

kernel/src/gdt.c

@@ -1,7 +1,6 @@
-#include "paging.h"
-#include "pmm.h"
 #include <kernel.h>
 #include <string.h>
+#include <errno.h>
 #include <gdt.h>
 
 static struct gdt_entries gdt;
@@ -105,8 +104,6 @@ int gdt_init(void) {
 	memset(&tss, 0, sizeof(tss));
 	tss_load(&tss);
 
-	debugf("[gdt] GDT loaded.\n");
-
-	return 0;
+	return SUCCESS;
 }
 

kernel/src/idt.c

@@ -1,5 +1,7 @@
 #include <kernel.h>
 #include <string.h>
+#include <system.h>
+#include <errno.h>
 #include <gdt.h>
 #include <idt.h>
 
@@ -7,25 +9,27 @@ __align(16) // performace
 static struct idt_entry idt[IDT_ENTRIES];
 static struct idt_pointer idtp;
 
-void idt_set_gate(uint8_t i, void* handler, uint8_t attrib) {
+void idt_set_gate(uint8_t i, void* handler, uint8_t attrib, uint8_t ist) {
 	size_t addr = (size_t)handler;
 	idt[i].offset_low = (uint16_t)addr;
 	idt[i].selector = GDT_KERNEL_CODE;
-	idt[i].ist = 0;
-	idt[i].__reserved = 0;
+	idt[i].ist = ist & 7;
 	idt[i].attrib = attrib;
 	idt[i].offset_mid = (uint16_t)(addr >> 16);
 	idt[i].offset_high = (uint32_t)(addr >> 32);
+	idt[i].__reserved = 0;
 }
 
 int idt_init(void) {
+	memset(idt, 0, sizeof(idt));
+
 	idtp.size = sizeof(idt) - 1;
-	idtp.offset = (size_t)&idt;
+	idtp.offset = (uintptr_t)&idt;
 
 	// Load IDT instruction
+	cli();
 	__asm__ volatile ("lidt %0" : : "m"(idtp));
 
-	debugf("[idt] IDT initalized.\n");
-	return 0;
+	return SUCCESS;
 }
 

kernel/src/isr.c

@@ -2,6 +2,7 @@
 #include <serial.h>
 #include <string.h>
 #include <system.h>
+#include <errno.h>
 #include <idt.h>
 #include <isr.h>
 
@@ -64,24 +65,23 @@ void pic_remap(void) {
 int isr_init(void) {
 	memset(irq_handlers, 0, sizeof(irq_handlers));
 
-	if (idt_init() != 0) {
-		debugf("[isr] Could not load IDT.");
-		return 1;
-	}
+	idt_init();
 
 	for (int i = 0; i < 48; i++) {
 		// First 32 IRSs are exceptions (traps) and the next 16 are hardware interrupts
-		idt_set_gate(i, isr_redirect_table[i], IDT_FLAG_INT);
+		idt_set_gate(i, isr_redirect_table[i], i < 32 ? IDT_FLAG_TRAP : IDT_FLAG_INT, 0);
 	}
-	idt_set_gate(0x03, isr_redirect_table[3], IDT_FLAG_USER); // Allow breakpoints
-	idt_set_gate(0x80, isr128, IDT_FLAG_USER); // Syscall
+
+	idt_set_gate(0x02, isr_redirect_table[2], IDT_FLAG_TRAP, 2); // Use IST2 for NMIs
+	idt_set_gate(0x03, isr_redirect_table[3], IDT_FLAG_USER, 0); // Allow breakpoints
+	idt_set_gate(0x08, isr_redirect_table[8], IDT_FLAG_TRAP, 1); // Use IST1 for Double Faults
+	idt_set_gate(0x80, isr128, IDT_FLAG_USER, 0); // Syscall
 	
 	pic_remap();
 	// TODO: apic_init();
 
 	sti();
-	debugf("[isr] ISR initialized.\n");
-	return 0;
+	return SUCCESS;
 }
 
 void isr_register(uint8_t i, isr_handler_ptr handler) {

kernel/src/kernel.c

@@ -1,5 +1,4 @@
 #include <bootloader.h>
-#include <kmalloc.h>
 #include <paging.h>
 #include <serial.h>
 #include <splash.h>
@@ -13,10 +12,10 @@
 __noreturn
 void _start(void) {
 	// Serial console for debugging
-	if (serial_init(COM1) != 0) panic("Failed to initialize Serial driver.");
+	if (serial_init(COM1) < 0) panic("Failed to initialize Serial driver.");
 
 	// Load structures from bootloader
-	if (boot_init() != 0) panic("Failed to parse bootloader structures.");
+	if (boot_init() < 0) panic("Failed to parse bootloader structures.");
 
 	// The most important function in the world.
 	splash();
@@ -28,12 +27,12 @@ void _start(void) {
 	debugf("[kernel] CPUID_GETVENDORID: %s\n", s);
 
 	// System init
-	if (gdt_init() != 0) panic("Failed to initalize GDT.");
-	if (isr_init() != 0) panic("Failed to initalize ISRs.");
+	if (gdt_init() < 0) panic("Failed to initalize GDT.");
+	if (isr_init() < 0) panic("Failed to initalize ISRs.");
 
 	// Memory management
-	if (pmm_init() != 0) panic("Failed to initalize Physical Memory Manager.");
-	if (pag_init() != 0) panic("Failed to initalize Paging.");
+	if (pmm_init() < 0) panic("Failed to initalize Physical Memory Manager.");
+	if (pag_init() < 0) panic("Failed to initalize Paging.");
 
 	// Patiently wait for things to do :)
 	while (1);

kernel/src/paging.c

@@ -3,6 +3,7 @@
 #include <limine.h>
 #include <string.h>
 #include <serial.h>
+#include <errno.h>
 #include <pmm.h>
 
 #include <paging.h>
@@ -12,19 +13,17 @@ uint64_t* pag_kernel_pml4 = NULL;
 
 int pag_init(void) {
 	pag_kernel_pml4 = TO_VIRT(pmm_alloc());
-	if (pag_kernel_pml4 == NULL) {
-		debugf("[pag] Failed to allocate kernel PML4. Not enough memory.\n");
-		return 1;
-	}
+	if (IS_ERR(pag_kernel_pml4)) return PTR_ERR(pag_kernel_pml4);
 	memset(pag_kernel_pml4, 0, PAGE_SIZE);
 
-	pag_map_region(
+	int ret = pag_map_region(
 		pag_kernel_pml4, 
 		(void*)bootloader.kernel_virt_base, 
 		(void*)bootloader.kernel_phys_base, 
 		dceil(bootloader.executable->size, PAGE_SIZE), 
 		PTE_FLAG_WRITE | PTE_FLAG_PRESENT
 	);
+	if (ret != SUCCESS) return ret;
 
 	for (size_t i = 0; i < bootloader.mm_entry_count; i++) {
 		struct limine_memmap_entry* entry = bootloader.mm_entries[i];
@@ -48,115 +47,106 @@ int pag_init(void) {
 			continue;
 		}
 
-		pag_map_region(
+		ret = pag_map_region(
 			pag_kernel_pml4,
 			(void*)(entry->base + bootloader.hhdm_offset), (void*)entry->base,
 			dceil(entry->length, PAGE_SIZE),
 			flags | PTE_FLAG_PRESENT
 		);
+		if (ret != SUCCESS) return ret;
 	}
 
-	debugf("[pag] Switching to kernel PML4 at %p.\n", pag_kernel_pml4);
 	pag_set_pml4(pag_kernel_pml4);
 
-	debugf("[pag] Paging initialized.\n");
 	return 0;
 }
 
 uint64_t* pag_get_pte(uint64_t* pml4, void* vaddr) {
 	uintptr_t v = (uintptr_t)vaddr;
-	if (v % PAGE_SIZE != 0) {
-		debugf("[pag] Could not get PTE from non-aligned virtual address %p.\n", vaddr);
-		return NULL;
-	}
+	if (v % PAGE_SIZE != 0) return ERR_PTR(-EALIGN);
 
 	uint64_t* pdpt = pag_get_next_tab(pml4,	PML4_IDX(v));
-	if (pdpt == NULL) {
-		debugf("[pag] Could not get PTE. %p was not found in PML4.\n");
-		return NULL;
-	}
+	if (IS_ERR(pdpt)) return pdpt;
+
 	uint64_t* pd = pag_get_next_tab(pdpt, PDPT_IDX(v));
-	if (pd == NULL) {
-		debugf("[pag] Could not get PTE. %p was not found in PDPT.\n");
-		return NULL;
-	}
+	if (IS_ERR(pd)) return pd;
+
 	uint64_t* pt = pag_get_next_tab(pd, PD_IDX(v));
-	if (pt == NULL) {
-		debugf("[pag] Could not get PTE. %p was not found in PD.\n");
-		return NULL;
-	}
+	if (IS_ERR(pt)) return pt;
 
 	return &pt[PT_IDX(v)];
 }
 
 uint64_t* pag_new_pte(uint64_t* pml4, void* vaddr) {
 	uintptr_t v = (uintptr_t)vaddr;
-	if (v % PAGE_SIZE != 0) {
-		debugf("[pag] Could not create PTE for non-aligned virtual address %p.\n", vaddr);
-		return NULL;
-	}
+	if (v % PAGE_SIZE != 0) return ERR_PTR(-EALIGN);
 
 	uint64_t* pdpt = pag_new_next_tab(pml4,	PML4_IDX(v));
-	if (pdpt == NULL) {
-		debugf("[pag] Failed to create PDPT. Not enough memory.\n");
-		return NULL;
-	}
+	if (IS_ERR(pdpt)) return pdpt;
+
 	uint64_t* pd = pag_new_next_tab(pdpt, PDPT_IDX(v));
-	if (pd == NULL) {
-		debugf("[pag] Failed to create PD. Not enough memory.\n");
-		if (pdpt != NULL) pmm_free(pdpt);
-		return NULL;
-	}
+	if (IS_ERR(pd)) return pd;
+
 	uint64_t* pt = pag_new_next_tab(pd, PD_IDX(v));
-	if (pt == NULL) {
-		debugf("[pag] Failed to create PT. Not enough memory.\n");
-		if (pd != NULL) pmm_free(pd);
-		if (pdpt != NULL) pmm_free(pdpt);
-		return NULL;
-	}
+	if (IS_ERR(pt)) return pt;
 
 	return &pt[PT_IDX(v)];
 }
 
-void pag_map(uint64_t* pml4, void* vaddr, void* paddr, uint64_t flags) {
+int pag_map(uint64_t* pml4, void* vaddr, void* paddr, uint64_t flags) {
 	uintptr_t p = (uintptr_t)paddr;
-	if (p % PAGE_SIZE != 0) {
-		debugf("[pag] Could not map %p to %p. Physical address is not aligned.\n", paddr, vaddr);
-		return;
-	}
-	
-	uint64_t* page = pag_new_pte(pml4, vaddr);
-	*page = PTE_ADDR(p) | flags | PTE_FLAG_PRESENT;
+	if (p % PAGE_SIZE != 0) return -EALIGN;
+
+	uint64_t* pte = pag_new_pte(pml4, vaddr);
+	if (IS_ERR(pte)) return PTR_ERR(pte);
+
+	*pte = PTE_ADDR(p) | flags | PTE_FLAG_PRESENT;
 	pag_invalidate(vaddr);
+
+	return SUCCESS;
 }
 
-void pag_map_region(uint64_t* pml4, void* vaddr, void* paddr, size_t count, uint64_t flags) {
+int pag_map_region(uint64_t* pml4, void* vaddr, void* paddr, size_t count, uint64_t flags) {
 	for (size_t i = 0; i < count; i++) {
-		pag_map(pml4, vaddr + i * PAGE_SIZE, paddr + i * PAGE_SIZE, flags);
+		int ret = pag_map(pml4, vaddr + i * PAGE_SIZE, paddr + i * PAGE_SIZE, flags);
+		if (ret != SUCCESS) return ret;
 	}
+	return SUCCESS;
 }
 
 // TODO: This is a pmm memory leak. If all pages in a PT are unmapped, remove
 // that PT from it's PD. This applies to PDs & PDPTs too.
-void pag_unmap(uint64_t* pml4, void* vaddr) {
+int pag_unmap(uint64_t* pml4, void* vaddr) {
 	uint64_t* pte = pag_get_pte(pml4, vaddr);
+	if (IS_ERR(pte)) return PTR_ERR(pte);
+
 	*pte = 0;
 	pag_invalidate(vaddr);
+
+	return SUCCESS;
 }
 
-void pag_unmap_region(uint64_t* pml4, void* vaddr, size_t count) {
+int pag_unmap_region(uint64_t* pml4, void* vaddr, size_t count) {
 	for (size_t i = 0; i < count; i++) {
-		pag_unmap(pml4, vaddr + i * PAGE_SIZE);
+		int ret = pag_unmap(pml4, vaddr + i * PAGE_SIZE);
+		if (ret != SUCCESS) return ret;
 	}
+	return SUCCESS;
 }
 
-void pag_protect(uint64_t* pml4, void* vaddr, uint64_t flags) {
+int pag_protect(uint64_t* pml4, void* vaddr, uint64_t flags) {
 	uint64_t* pte = pag_get_pte(pml4, vaddr);
+	if (IS_ERR(pte)) return PTR_ERR(pte);
+
 	*pte = PTE_ADDR(*pte) | flags | PTE_FLAG_PRESENT;
+
+	return SUCCESS;
 }
 
 void* pag_get_phys(uint64_t* pml4, void* vaddr) {
 	uint64_t* pte = pag_get_pte(pml4, vaddr);
+	if (IS_ERR(pte)) return pte;
+
 	return (void*)PTE_ADDR(*pte);
 }
 
@@ -171,21 +161,20 @@ uint64_t* pag_get_pml4(void) {
 }
 
 uint64_t* pag_get_next_tab(uint64_t* tab, offset_t index) {
-	if (index >= 512 || tab == NULL) return NULL;
-	else if (tab[index] & PTE_FLAG_PRESENT) return TO_VIRT(tab[index] & PTE_ADDR_MASK);
-	else return NULL;
+	if (tab == NULL || IS_ERR(tab)) return ERR_PTR(-EFAULT);
+	if (index >= 512) return ERR_PTR(-EINVAL);
+
+	if (tab[index] & PTE_FLAG_PRESENT) return TO_VIRT(PTE_ADDR(tab[index]));
+	else return ERR_PTR(-ENOENT);
 }
 
 uint64_t* pag_new_next_tab(uint64_t* tab, offset_t index) {
-	if (tab == NULL) return NULL;
 	uint64_t* vaddr = pag_get_next_tab(tab, index);
-	if (vaddr != NULL) return vaddr;
+	if (!IS_ERR(vaddr)) return vaddr;
+	if (PTR_ERR(vaddr) != -ENOENT) return vaddr;
 
 	void* paddr = pmm_alloc();
-	if (!paddr) {
-		debugf("[pag] Failed to allocate page for new table.\n");
-		return NULL;
-	}
+	if (IS_ERR(paddr)) return paddr;
 
 	vaddr = TO_VIRT(paddr);
 	memset(vaddr, 0, PAGE_SIZE);

kernel/src/pmm.c

@@ -3,6 +3,7 @@
 #include <limine.h>
 #include <paging.h>
 #include <serial.h>
+#include <errno.h>
 
 #include <pmm.h>
 
@@ -10,7 +11,6 @@ uint64_t* pmm_head = NULL;
 size_t pmm_total_mem = 0;
 
 int pmm_init(void) {
-
 	debugf("[pmm] Physical memory map:\n"); // We're gonna use the loop to also print the memmap
 	for (size_t i = 0; i < bootloader.mm_entry_count; i++) {
 		struct limine_memmap_entry* entry = bootloader.mm_entries[i];
@@ -39,37 +39,29 @@ int pmm_init(void) {
 	}
 
 	debugf("[pmm] %d bytes of available memory.\n", pmm_total_mem);
+	if (pmm_total_mem == 0) return -ENOMEM;
 
-	return 0;
+	return SUCCESS;
 }
 
 void* pmm_alloc() {
-	if (pmm_head == NULL) {
-		debugf("[pmm] Could not allocate page, not enough memory.\n");
-		return NULL;
-	}
+	if (pmm_head == NULL) return ERR_PTR(-ENOMEM);
+
 	uint64_t* addr = pmm_head;
-	if ((uintptr_t)addr % PAGE_SIZE != 0) {
-		debugf("[pmm] Tried to allocate non-aligned page.\n");
-		// It may fix itself if a page gets freed
-		// panic("pmm_head corrupted."); 
-		return NULL;
-	}
+	if ((uintptr_t)addr % PAGE_SIZE != 0) panic("pmm_head corrupted.");
 	pmm_head = (uint64_t*)(*addr);
+
 	return TO_PHYS(addr);
 }
 
-void pmm_free(void* page) {
-	if (page == NULL) {
-		debugf("[pmm] Tried to free NULL.\n");
-		return;
-	}
-	if ((uintptr_t)page % PAGE_SIZE != 0) {
-		debugf("[pmm] Tried to free non-aligned page.\n");
-		return;
-	}
+int pmm_free(void* page) {
+	if (page == NULL || IS_ERR(page)) return -EFAULT;
+	if ((uintptr_t)page % PAGE_SIZE != 0) return -EALIGN;
+
 	uint64_t* addr = TO_VIRT(page);
 	*addr = (uint64_t)pmm_head;
 	pmm_head = addr;
+
+	return SUCCESS;
 }
 

kernel/src/serial.c

@@ -1,3 +1,4 @@
+#include "errno.h"
 #include <vsnprintf.h>
 #include <kernel.h>
 #include <system.h>
@@ -11,13 +12,15 @@ int serial_init(int dev) {
 	outb(dev + 3, 0x03);	// 8 bits, no parity, one stop bit
 	outb(dev + 2, 0xC7);	// Enable FIFO, clear them, with 14 byte threshold
 	outb(dev + 4, 0x0B);	// IRQs enabled, RTS/DSR set
+
 	outb(dev + 4, 0x1E);	// Set in loopback mode, test the serial chip
 	outb(dev + 0, 0xAE);	// Test serial chip (send byte 0xAE and check if it returns)
-	
-	if (inb(dev + 0) != 0xAE) return 1;
+	if (inb(dev + 0) != 0xAE) return -ENODEV;
+
 	outb(dev + 4, 0x0F);	// non-loopback, IRQs enabled, OUT#1 and OUT#2 bits enabled
 	
-	debugf("\x1b[H\x1b[JSerial display initiated!\n\n");
+	serial_cls(COM1);
+	serial_puts(COM1, "Serial display (COM1)\n\n");
 	
 	return 0;
 }
@@ -54,6 +57,10 @@ void serial_puts(int dev, char* s) {
 	serial_write(dev, s, len);
 }
 
+void serial_cls(int dev) {
+	serial_write(dev, "\x1b[H\x1b[J", 6);
+}
+
 int debugf(char* fmt, ...) {
 	va_list args;
 	va_start(args, fmt);