Create fat16.c

Add implementation for fat16 filesystem

Makefile

@@ -8,8 +8,13 @@ OBJCOPY = i386-elf-objcopy
 BUILD_DIR = build
 CROSS_DIR = cross
 DISK_IMG = $(BUILD_DIR)/disk.img
+
+STAGE2_ADDR = 0x7e00
 STAGE2_SIZE = 2048
 
+# Place the memory map (e820) past stage2 bl in memory
+MEMMAP_BASE = $(shell echo $$(($(STAGE2_ADDR) + $(STAGE2_SIZE))))
+
 KERNEL_C_SRC = $(wildcard kernel/*.c)
 KERNEL_ASM_SRC = $(wildcard kernel/*.asm)
 KERNEL_OBJ = $(patsubst kernel/%.c, $(BUILD_DIR)/%.o, $(KERNEL_C_SRC))
@@ -29,7 +34,7 @@ stage1: $(BUILD_DIR)
 # NOTE: Stage2 final size should be checked against `$(STAGE2_SIZE)` by the build system to avoid an overflow.
 # Alternatively, convey the final stage2 size through other means to stage1.
 stage2: $(BUILD_DIR)
-	$(AS) $(ASFLAGS) -o $(BUILD_DIR)/stage2.o bootloader/stage2.asm
+	$(AS) $(ASFLAGS) -DMEMMAP_BASE=$(MEMMAP_BASE) -o $(BUILD_DIR)/stage2.o bootloader/stage2.asm
 	$(CC) -std=c11 -ffreestanding -nostdlib -nostdinc -fno-stack-protector -m32 -Iklibc/include -g -c -o $(BUILD_DIR)/stage2_load.o bootloader/stage2_load.c
 	$(LD) -Tbootloader/stage2.ld -melf_i386 -o $(BUILD_DIR)/$@.elf $(BUILD_DIR)/stage2.o $(BUILD_DIR)/stage2_load.o
 	$(OBJCOPY) -O binary $(BUILD_DIR)/$@.elf $(BUILD_DIR)/$@.bin
@@ -39,7 +44,7 @@ $(BUILD_DIR)/asm_%.o: kernel/%.asm
 	$(AS) $(ASFLAGS) -o $@ $<
 
 $(BUILD_DIR)/%.o: kernel/%.c
-	$(CC) -std=c11 -ffreestanding -nostdlib -nostdinc -fno-stack-protector -m32 -Iklibc/include -g -c -o $@ $<
+	$(CC) -DMEMMAP_BASE=$(MEMMAP_BASE) -std=c11 -ffreestanding -nostdlib -nostdinc -fno-stack-protector -m32 -Iklibc/include -g -c -o $@ $<
 
 $(BUILD_DIR)/klibc/%.o: klibc/src/%.c
 	$(CC) -std=c11 -ffreestanding -nostdlib -nostdinc -fno-stack-protector -m32 -Iklibc/include -g -c -o $@ $<

bootloader/README.md

@@ -11,16 +11,16 @@ Bootloader documentation for ClassicOS
 
 ## Stage 1 (`stage1.asm`)
 
-Responsible for loading the second stage using BIOS routines, and switching to protected mode.
-
 - Queries CHS parameters from BIOS
 - Loads the second stage bootloader (2048 B) to `0x7c00`
-- Sets up a GDT with descriptor entries for code and data both covering the whole 32-bit address space
 - Enables A20
-- Set CR0.PE (enable protected mode) and jump to stage 2
+- Jumps to stage2
 
 ## Stage 2 (`stage2.asm, stage2_load.c`)
 
+- Read and store E820 memory map from BIOS
+- Sets up a GDT with descriptor entries for code and data both covering the whole 32-bit address space
+- Set CR0.PE (enable protected mode)
 - Set up segment registers
 - Load the kernel ELF header
 - Parse the program headers, and load all `PT_LOAD` segments from disk

bootloader/stage1.asm

@@ -40,11 +40,8 @@ _start:
     call enable_a20
     jc a20_error                ; Jump if A20 enable fails
 
-    ; Setup Global Descriptor Table
-    call setup_gdt
-
-    ; Switch to protected mode and jump to second stage at 0x08:0x7E00
-    call switch_to_pm
+    ; Jump to s2
+    jmp 0x7e00
 
 disk_error:
     mov si, disk_error_msg
@@ -241,30 +238,6 @@ check_a20:
     clc                      ; Clear carry flag to indicate success
     ret
 
-; ----------------------------------------------------------------
-gdt_start:
-    dq 0x0000000000000000         ; Null descriptor
-    dq 0x00CF9A000000FFFF         ; 32-bit code segment (selector 0x08)
-    dq 0x00CF92000000FFFF         ; 32-bit data segment (selector 0x10)
-    dq 0x00009A000000FFFF         ; 16-bit code segment for real mode (selector 0x18)
-
-gdt_descriptor:
-    dw gdt_end - gdt_start - 1
-    dd gdt_start
-gdt_end:
-
-setup_gdt:
-    lgdt [gdt_descriptor]
-    ret
-
-; ----------------------------------------------------------------
-switch_to_pm:
-    cli
-    mov eax, cr0
-    or eax, 1
-    mov cr0, eax
-    jmp 0x08:0x7E00             ; jump to S2
-
 ; ----------------------------------------------------------------
 print_string_16:
 .loop:

bootloader/stage2.asm

@@ -1,10 +1,80 @@
-[BITS 32]
 global _start
-global ata_lba_read
-
 extern load_kernel
 
+%define e820_magic 0x534d4150 ; "SMAP"
+%define e820_entry_size 24
+%define e820_max_entries 128
+
+; ----------------------------------------------------------------
+; Real mode
+; ----------------------------------------------------------------
+[BITS 16]
 _start:
+    call read_e820
+    call setup_gdt
+    call switch_to_pm
+
+read_e820:
+    xor ebx, ebx
+    mov es, bx
+    mov di, MEMMAP_BASE+4       ; ES=0 DI=MEMMAP_BASE+4
+    xor bp, bp                  ; Keeping count in bp
+
+.e820_loop:
+    mov eax, 0xe820
+    mov ecx, e820_entry_size
+    mov edx, e820_magic
+    int 0x15
+    jc .done                    ; Error?
+
+    cmp eax, e820_magic         ; Verify "SMAP"
+    jne .done
+
+    test ecx, ecx               ; Skip 0-sized entries
+    jz .skip
+
+    add di, e820_entry_size     ; Advance write addr
+    inc bp                      ; Increment count
+
+    cmp bp, e820_max_entries    ; Stop if we're at capacity
+    jae .done
+.skip:
+    test ebx, ebx
+    jne .e820_loop
+.done:
+    mov [MEMMAP_BASE], bp       ; Store count
+    ret
+
+setup_gdt:
+    lgdt [gdt_descriptor]
+    ret
+
+switch_to_pm:
+    cli
+    mov eax, cr0
+    or eax, 1
+    mov cr0, eax
+    jmp 0x08:pm_entry
+
+e820_count:
+    dw 0
+
+gdt_start:
+    dq 0x0000000000000000         ; Null descriptor
+    dq 0x00CF9A000000FFFF         ; 32-bit code segment (selector 0x08)
+    dq 0x00CF92000000FFFF         ; 32-bit data segment (selector 0x10)
+    dq 0x00009A000000FFFF         ; 16-bit code segment for real mode (selector 0x18)
+gdt_descriptor:
+    dw gdt_end - gdt_start - 1
+    dd gdt_start
+gdt_end:
+
+; ----------------------------------------------------------------
+; Protected mode
+; ----------------------------------------------------------------
+[BITS 32]
+
+pm_entry:
     ; Set up segments
     ; Data segments
     mov ax, 0x10
@@ -18,9 +88,8 @@ _start:
     mov ax, 0x08
     mov cs, ax
 
-    ; Stack (must be identity-mapped)
+    ; Stack
     mov esp, 0x90000
 
     call load_kernel
-
     jmp eax

kernel/fat16.c

@@ -0,0 +1,107 @@
+#include "fat16.h"
+#include "ata.h"   // Use ata_read_sector and ata_write_sector
+#include "print.h" // For debugging
+#include <string.h> // For string manipulation
+
+// Global variables
+static fat16_boot_sector_t boot_sector;
+static uint32_t root_dir_sector = FAT16_ROOT_DIR_SECTOR;
+
+// Read a sector from the disk using ATA
+bool read_sector(uint32_t lba, uint8_t* buffer) {
+    return ata_read_sector(lba, buffer);
+}
+
+// Write a sector to the disk using ATA
+bool write_sector(uint32_t lba, const uint8_t* buffer) {
+    return ata_write_sector(lba, buffer);
+}
+
+// Parse the boot sector to retrieve basic file system info
+bool parse_fat16_boot_sector(void) {
+    uint8_t sector_buffer[FAT16_SECTOR_SIZE];
+
+    // Read the boot sector
+    if (!read_sector(FAT16_BOOT_SECTOR, sector_buffer)) {
+        print_string("[FAT16] Failed to read boot sector\n");
+        return false;
+    }
+
+    // Cast to boot sector structure
+    memcpy(&boot_sector, sector_buffer, sizeof(fat16_boot_sector_t));
+
+    // Check for FAT16 signature
+    if (boot_sector.oem_name[0] != 'F' || boot_sector.oem_name[1] != 'A' || boot_sector.oem_name[2] != 'T') {
+        print_string("[FAT16] Invalid FAT16 boot sector signature\n");
+        return false;
+    }
+
+    print_string("[FAT16] FAT16 boot sector parsed successfully\n");
+    return true;
+}
+
+// Parse the root directory
+bool parse_fat16_root_dir(void) {
+    uint8_t sector_buffer[FAT16_SECTOR_SIZE];
+
+    for (int i = 0; i < (boot_sector.max_root_entries / (FAT16_SECTOR_SIZE / sizeof(fat16_dir_entry_t))); i++) {
+        // Read root directory sector
+        if (!read_sector(root_dir_sector + i, sector_buffer)) {
+            print_string("[FAT16] Failed to read root directory sector\n");
+            return false;
+        }
+
+        // Parse the root directory entries
+        for (int j = 0; j < (FAT16_SECTOR_SIZE / sizeof(fat16_dir_entry_t)); j++) {
+            fat16_dir_entry_t* entry = (fat16_dir_entry_t*)&sector_buffer[j * sizeof(fat16_dir_entry_t)];
+            if (entry->name[0] == 0x00) {
+                // End of directory entries
+                return true;
+            }
+            if (entry->name[0] != 0xE5) {
+                // Print file name (8.3 format)
+                char filename[12];
+                strncpy(filename, (char*)entry->name, 8);
+                filename[8] = '.';
+                strncpy(&filename[9], (char*)entry->ext, 3);
+                filename[11] = '\0';
+                print_string(filename);
+                print_string("\n");
+            }
+        }
+    }
+    return true;
+}
+
+// Read a specific directory entry from the FAT16 root directory
+bool read_fat16_entry(uint16_t entry_index, fat16_dir_entry_t* entry) {
+    uint8_t sector_buffer[FAT16_SECTOR_SIZE];
+    uint32_t sector_num = FAT16_ROOT_DIR_SECTOR + (entry_index / (FAT16_SECTOR_SIZE / sizeof(fat16_dir_entry_t)));
+    uint16_t entry_offset = entry_index % (FAT16_SECTOR_SIZE / sizeof(fat16_dir_entry_t));
+
+    // Read the sector
+    if (!read_sector(sector_num, sector_buffer)) {
+        print_string("[FAT16] Failed to read root directory sector\n");
+        return false;
+    }
+
+    // Get the entry
+    memcpy(entry, &sector_buffer[entry_offset * sizeof(fat16_dir_entry_t)], sizeof(fat16_dir_entry_t));
+    return true;
+}
+
+// Mount the FAT16 filesystem
+bool mount_fat16(void) {
+    // Parse the boot sector
+    if (!parse_fat16_boot_sector()) {
+        return false;
+    }
+
+    // Parse the root directory
+    if (!parse_fat16_root_dir()) {
+        return false;
+    }
+
+    print_string("[FAT16] Filesystem mounted successfully\n");
+    return true;
+}

kernel/fat16.h

@@ -0,0 +1,60 @@
+#ifndef FAT16_H
+#define FAT16_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+/* FAT16 Constants */
+#define FAT16_SECTOR_SIZE        512
+#define FAT16_CLUSTER_SIZE       1
+#define FAT16_MAX_FILENAME_LEN   11   // 8.3 format
+#define FAT16_ROOT_DIR_ENTRIES   224  // Fat16 root directory entries (typically 512 bytes per entry)
+
+#define FAT16_BOOT_SECTOR        0
+#define FAT16_FAT1_SECTOR        1
+#define FAT16_FAT2_SECTOR        2
+#define FAT16_ROOT_DIR_SECTOR    19  // First sector of root directory
+
+/* Boot Sector */
+typedef struct {
+    uint8_t jmp[3];               // Jump instruction to code
+    uint8_t oem_name[8];          // OEM Name
+    uint16_t bytes_per_sector;    // Bytes per sector (512)
+    uint8_t sectors_per_cluster;  // Sectors per cluster
+    uint16_t reserved_sectors;    // Reserved sectors
+    uint8_t num_fats;             // Number of FAT tables
+    uint16_t max_root_entries;    // Max number of root directory entries
+    uint16_t total_sectors_16;    // Total sectors in FAT16
+    uint8_t media_type;           // Media type (0xF8 = fixed drive)
+    uint16_t sectors_per_fat;    // Sectors per FAT table
+    uint16_t sectors_per_track;  // Sectors per track (for CHS addressing)
+    uint16_t num_heads;          // Number of heads (for CHS addressing)
+    uint32_t hidden_sectors;     // Hidden sectors (before the partition)
+    uint32_t total_sectors_32;   // Total sectors in FAT16 (extended)
+} __attribute__((packed)) fat16_boot_sector_t;
+
+/* FAT16 Directory Entry */
+typedef struct {
+    uint8_t name[8];   // File name (8 chars)
+    uint8_t ext[3];    // File extension (3 chars)
+    uint8_t attributes; // File attributes (e.g., directory, read-only)
+    uint8_t reserved;   // Reserved
+    uint8_t creation_time[2]; // Creation time
+    uint8_t creation_date[2]; // Creation date
+    uint8_t last_access_date[2]; // Last access date
+    uint8_t first_cluster_high[2]; // High part of first cluster number
+    uint8_t last_mod_time[2];  // Last modification time
+    uint8_t last_mod_date[2];  // Last modification date
+    uint8_t first_cluster_low[2];  // Low part of first cluster number
+    uint32_t file_size;         // File size in bytes
+} __attribute__((packed)) fat16_dir_entry_t;
+
+/* Function Prototypes */
+bool mount_fat16(void);
+bool read_sector(uint32_t lba, uint8_t* buffer);
+bool write_sector(uint32_t lba, const uint8_t* buffer);
+bool parse_fat16_boot_sector(void);
+bool parse_fat16_root_dir(void);
+bool read_fat16_entry(uint16_t entry_index, fat16_dir_entry_t* entry);
+
+#endif // FAT16_H

kernel/memmap.c

@@ -1,19 +1,16 @@
 #include "memmap.h"
 
+#define BOOTLOADER_MEMMAP_COUNT_ADDR    MEMMAP_BASE
+#define BOOTLOADER_MEMMAP_ADDR          (MEMMAP_BASE + 4)
+
 uint32_t get_memory_map(memory_map_entry_t *map, uint32_t max_entries) {
+    // Read the number of entries found by the bootloader
+    uint32_t entries_found = *(uint32_t*)BOOTLOADER_MEMMAP_COUNT_ADDR;
+    memory_map_entry_t *bios_data = (memory_map_entry_t*)BOOTLOADER_MEMMAP_ADDR;
+
     uint32_t count = 0;
-
-    if (max_entries >= 1) {
-        map[count].base_addr = 0x00000000;
-        map[count].length = 0x0009FC00;
-        map[count].type = 1;
-        count++;
-    }
-
-    if (max_entries >= 2) {
-        map[count].base_addr = 0x00100000;
-        map[count].length = 0x1FF00000;
-        map[count].type = 1;
+    while (count < entries_found && count < max_entries) {
+        map[count] = bios_data[count];
         count++;
     }
 

kernel/memmap.h

@@ -7,6 +7,7 @@ typedef struct {
     uint64_t base_addr;
     uint64_t length;
     uint32_t type;
+    uint32_t ext;
 } __attribute__((packed)) memory_map_entry_t;
 
 uint32_t get_memory_map(memory_map_entry_t *map, uint32_t max_entries);

klibc/include/string.h

@@ -3,12 +3,13 @@
 
 #include <stddef.h>
 
-extern int memcmp(const void* s1, const void* s2, size_t n);
-extern void* memmove(void* dst, const void* src, size_t n);
-extern void* memcpy(void* dst, const void* src, size_t n);
-extern void* memset(void* dst, int c, size_t n);
+extern int memcmp(const void *s1, const void *s2, size_t n);
+extern void *memmove(void *dst, const void *src, size_t n);
+extern void *memcpy(void *dst, const void *src, size_t n);
+extern void *memset(void *dst, int c, size_t n);
 
-extern size_t strlen(const char* s);
-extern int strcmp(const char* s1, const char* s2);
+extern size_t strlen(const char *s);
+extern int strcmp(const char *s1, const char *s2);
+extern char *strncpy(char *dst, const char *src, size_t n);
 
 #endif  // CLASSICOS_KLIBC_STRING_H

klibc/src/string.c

@@ -1,8 +1,8 @@
 #include <string.h>
 
-int memcmp(const void* s1, const void* s2, size_t n) {
-    const unsigned char* c1 = s1;
-    const unsigned char* c2 = s2;
+int memcmp(const void *s1, const void *s2, size_t n) {
+    const unsigned char *c1 = s1;
+    const unsigned char *c2 = s2;
     int d = 0;
 
     while (n--) {
@@ -13,9 +13,9 @@ int memcmp(const void* s1, const void* s2, size_t n) {
     return d;
 }
 
-void* memmove(void* dst, const void* src, size_t n) {
-    const char* p = src;
-    char* q = dst;
+void *memmove(void *dst, const void *src, size_t n) {
+    const char *p = src;
+    char *q = dst;
 #if defined(__i386__) || defined(__x86_64__)
     if (q < p) {
         __asm__ volatile("cld; rep; movsb" : "+c"(n), "+S"(p), "+D"(q));
@@ -41,9 +41,9 @@ void* memmove(void* dst, const void* src, size_t n) {
     return dst;
 }
 
-void* memcpy(void* dst, const void* src, size_t n) {
-    const char* p = src;
-    char* q = dst;
+void *memcpy(void *dst, const void *src, size_t n) {
+    const char *p = src;
+    char *q = dst;
 #if defined(__i386__)
     size_t nl = n >> 2;
     __asm__ volatile("cld ; rep ; movsl ; movl %3,%0 ; rep ; movsb"
@@ -63,8 +63,8 @@ void* memcpy(void* dst, const void* src, size_t n) {
     return dst;
 }
 
-void* memset(void* dst, int c, size_t n) {
-    char* q = dst;
+void *memset(void *dst, int c, size_t n) {
+    char *q = dst;
 
 #if defined(__i386__)
     size_t nl = n >> 2;
@@ -86,15 +86,15 @@ void* memset(void* dst, int c, size_t n) {
     return dst;
 }
 
-size_t strlen(const char* s) {
-    const char* ss = s;
+size_t strlen(const char *s) {
+    const char *ss = s;
     while (*ss) ss++;
     return ss - s;
 }
 
-int strcmp(const char* s1, const char* s2) {
-    const unsigned char* c1 = (const unsigned char*)s1;
-    const unsigned char* c2 = (const unsigned char*)s2;
+int strcmp(const char *s1, const char *s2) {
+    const unsigned char *c1 = (const unsigned char *)s1;
+    const unsigned char *c2 = (const unsigned char *)s2;
     unsigned char ch;
     int d = 0;
 
@@ -105,3 +105,19 @@ int strcmp(const char* s1, const char* s2) {
 
     return d;
 }
+
+char *strncpy(char *dst, const char *src, size_t n) {
+    char *q = dst;
+    const char *p = src;
+    char ch;
+
+    while (n) {
+        n--;
+        *q++ = ch = *p++;
+        if (!ch) break;
+    }
+
+    memset(q, 0, n);
+
+    return dst;
+}