Refactor k_memcmp and implement disk_read_sector

Refactor memory comparison function and add disk read sector function.

.gitignore

@@ -1 +1,3 @@
+.build.env
 build
+cross

Makefile

@@ -1,8 +1,9 @@
 AS = nasm
 ASFLAGS = -f elf32 -g -F dwarf
-CC = gcc
-LD = ld
+CC = i386-elf-gcc
+LD = i386-elf-ld
 QEMU= qemu-system-i386
+OBJCOPY = i386-elf-objcopy
 
 BUILD_DIR = build
 DISK_IMG = $(BUILD_DIR)/disk.img
@@ -19,7 +20,7 @@ all: $(DISK_IMG)
 stage1: $(BUILD_DIR)
 	$(AS) $(ASFLAGS) -o $(BUILD_DIR)/$@.o bootloader/$@.asm
 	$(LD) -Ttext=0x7c00 -melf_i386 -o $(BUILD_DIR)/$@.elf $(BUILD_DIR)/$@.o
-	objcopy -O binary $(BUILD_DIR)/$@.elf $(BUILD_DIR)/$@.bin
+	$(OBJCOPY) -O binary $(BUILD_DIR)/$@.elf $(BUILD_DIR)/$@.bin
 
 # 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.
@@ -27,7 +28,7 @@ stage2: $(BUILD_DIR)
 	$(AS) $(ASFLAGS) -o $(BUILD_DIR)/stage2.o bootloader/stage2.asm
 	$(CC) -std=c11 -ffreestanding -nostdlib -fno-stack-protector -m32 -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
+	$(OBJCOPY) -O binary $(BUILD_DIR)/$@.elf $(BUILD_DIR)/$@.bin
 	truncate -s $(STAGE2_SIZE) $(BUILD_DIR)/$@.bin
 
 $(BUILD_DIR)/asm_%.o: kernel/%.asm
@@ -37,7 +38,7 @@ $(BUILD_DIR)/%.o: kernel/%.c
 	$(CC) -std=c11 -ffreestanding -nostdlib -fno-stack-protector -m32 -g -c -o $@ $<
 
 kernel: $(KERNEL_OBJ) | $(BUILD_DIR)
-	$(LD) -melf_i386 -Tbootloader/linker.ld -o $(BUILD_DIR)/kernel.elf $(KERNEL_OBJ)
+	$(LD) -melf_i386 -Tkernel/linker.ld -o $(BUILD_DIR)/kernel.elf $(KERNEL_OBJ)
 
 $(DISK_IMG): stage1 stage2 kernel
 	dd if=$(BUILD_DIR)/stage1.bin of=$@
@@ -56,3 +57,4 @@ gdb:
 
 clean:
 	rm -rf $(BUILD_DIR)
+	rm -rf $(CROSS_DIR)

README.md

@@ -35,6 +35,7 @@ You’ll need the following tools installed:
 - `qemu-system-i386`
 
 Optional:
+
 - `gdb`
 - `vncviewer` (TigerVNC or similar)
 
@@ -42,13 +43,27 @@ Optional:
 
 ## 🛠️ Building ClassicOS
 
-Clone and build:
+Clone repository:
 
-```bash
+```sh
 git clone https://github.com/gbowne1/ClassicOS.git
 cd ClassicOS
-make
 ```
 
-build kernel
-for %f in (*.c) do gcc -m32 -O0 -Wall -Wextra -Werror -pedantic -ffreestanding -nostdlib -fno-pic -fno-stack-protector -fno-pie -march=i386 -mtune=i386 -c "%f" -o "%f.o"
+Run `configure` script to build a cross-compiler toolchain for `i386-elf`:
+
+```sh
+./configure
+```
+
+Source the `.build.env` file to add the cross-compiler toolchain to your PATH:
+
+```sh
+source .build.env
+```
+
+Build the kernel:
+
+```sh
+make
+```

configure

@@ -0,0 +1,169 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Configuration
+TARGET="i386-elf"
+BINUTILS_VERSION="2.45"
+GCC_VERSION="15.2.0"
+
+# Paths
+SCRIPT_PATH="$(realpath "${BASH_SOURCE[0]}")"
+SCRIPT_DIR="$(dirname "$SCRIPT_PATH")"
+PREFIX="$SCRIPT_DIR/cross"
+SRC_DIR="$PREFIX/src"
+
+BINUTILS_SRC="$SRC_DIR/binutils-$BINUTILS_VERSION"
+BINUTILS_BUILD="$PREFIX/build-binutils"
+GCC_SRC="$SRC_DIR/gcc-$GCC_VERSION"
+GCC_BUILD="$PREFIX/build-gcc"
+
+# Flags
+DEBUG=0
+HELP=0
+
+# Parse arguments
+for arg in "$@"; do
+  case "$arg" in
+    -h|--help)
+      HELP=1
+      ;;
+    -d|--debug)
+      DEBUG=1
+      ;;
+    *)
+      echo "Unknown option: $arg"
+      echo "Use -h or --help for usage information"
+      exit 1
+      ;;
+  esac
+done
+
+# Show help
+if [[ "$HELP" -eq 1 ]]; then
+  cat << EOF
+Usage: $0 [OPTIONS]
+
+Build a cross-compiler toolchain for $TARGET.
+
+OPTIONS:
+  -h, --help     Show this help message
+  -d, --debug    Enable debug mode (set -x)
+
+This script will:
+  1. Download binutils $BINUTILS_VERSION and GCC $GCC_VERSION
+  2. Build and install them to: $PREFIX
+
+EOF
+  exit 0
+fi
+
+# Enable debug mode
+if [[ "$DEBUG" -eq 1 ]]; then
+  set -x
+fi
+
+# Print configuration
+cat << EOF
+
+=== Build Configuration ===
+Target       : $TARGET
+Prefix       : $PREFIX
+Binutils     : $BINUTILS_VERSION
+GCC          : $GCC_VERSION
+===========================
+
+EOF
+
+# Create directory structure
+echo "Setting up directories..."
+mkdir -p "$SRC_DIR"
+
+# Download sources
+cd "$SRC_DIR"
+
+if [[ ! -d "$BINUTILS_SRC" ]]; then
+  echo "Downloading binutils $BINUTILS_VERSION..."
+  wget "https://ftp.gnu.org/gnu/binutils/binutils-$BINUTILS_VERSION.tar.gz"
+  echo "Extracting binutils..."
+  tar xf "binutils-$BINUTILS_VERSION.tar.gz"
+  rm "binutils-$BINUTILS_VERSION.tar.gz"
+else
+  echo "Binutils source already exists, skipping download"
+fi
+
+if [[ ! -d "$GCC_SRC" ]]; then
+  echo "Downloading GCC $GCC_VERSION..."
+  wget "https://ftp.gnu.org/gnu/gcc/gcc-$GCC_VERSION/gcc-$GCC_VERSION.tar.gz"
+  echo "Extracting GCC..."
+  tar xf "gcc-$GCC_VERSION.tar.gz"
+  rm "gcc-$GCC_VERSION.tar.gz"
+else
+  echo "GCC source already exists, skipping download"
+fi
+
+# Download GCC prerequisites
+if [[ ! -d "$GCC_SRC/gmp" ]]; then
+  echo "Downloading GCC prerequisites..."
+  cd "$GCC_SRC"
+  ./contrib/download_prerequisites
+  cd "$SRC_DIR"
+else
+  echo "GCC prerequisites already downloaded, skipping"
+fi
+
+# Build binutils
+if [[ ! -f "$PREFIX/bin/$TARGET-ld" ]]; then
+  echo "Building binutils..."
+  mkdir -p "$BINUTILS_BUILD"
+  cd "$BINUTILS_BUILD"
+
+  "$BINUTILS_SRC/configure" \
+    --target="$TARGET" \
+    --prefix="$PREFIX" \
+    --with-sysroot \
+    --disable-nls \
+    --disable-werror
+
+  make -j"$(nproc)"
+  make install
+else
+  echo "Binutils already installed, skipping build"
+fi
+
+# Build GCC
+if [[ ! -f "$PREFIX/bin/$TARGET-gcc" ]]; then
+  echo "Building GCC..."
+  mkdir -p "$GCC_BUILD"
+  cd "$GCC_BUILD"
+
+  "$GCC_SRC/configure" \
+    --target="$TARGET" \
+    --prefix="$PREFIX" \
+    --disable-nls \
+    --enable-languages=c \
+    --without-headers
+
+  make all-gcc -j"$(nproc)"
+  make all-target-libgcc -j"$(nproc)"
+  make install-gcc
+  make install-target-libgcc
+else
+  echo "GCC already installed, skipping build"
+fi
+
+cd "$SCRIPT_DIR"
+
+# Generate .build.env file
+cat > .build.env << EOF
+# Generated by configure on $(date)
+# Source this file to add the cross-compiler toolchain to your PATH
+export PATH="$PREFIX/bin:\$PATH"
+EOF
+
+echo ""
+echo "=== Build Complete ==="
+echo "Toolchain installed to: $PREFIX"
+echo ""
+echo "To use the toolchain, run:"
+echo "  source .build.env"
+echo "======================"

kernel/context_switch.s

@@ -0,0 +1,25 @@
+.global ctx_switch
+
+; void ctx_switch(uint32_t **old_sp_ptr, uint32_t *new_sp);
+; Arguments on stack (cdecl convention):
+; [ESP + 4] -> old_sp_ptr (pointer to the 'stack_ptr' field of current task)
+; [ESP + 8] -> new_sp     (value of 'stack_ptr' of the next task)
+
+ctx_switch:
+    ; 1. Save the context of the CURRENT task
+    pushf               ; Save EFLAGS (CPU status flags)
+    pusha               ; Save all General Purpose Regs (EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI)
+
+    ; 2. Save the current stack pointer (ESP) into the pointer passed as 1st arg
+    mov eax, [esp + 40] ; Get 1st argument (old_sp_ptr). Offset 40 = 36 (regs) + 4 (ret addr)
+    mov [eax], esp      ; *old_sp_ptr = ESP
+
+    ; 3. Load the stack pointer of the NEW task
+    mov esp, [esp + 44] ; Get 2nd argument (new_sp). Offset 44 = 40 + 4
+
+    ; 4. Restore the context of the NEW task
+    popa                ; Restore all General Purpose Regs
+    popf                ; Restore EFLAGS
+
+    ; 5. Jump to the new task (The 'ret' pops EIP from the new stack)
+    ret

kernel/fat12.c

@@ -1,5 +1,178 @@
 #include "fat12.h"
+#include "floppy.h"
+#include <stddef.h>
 
-void fat12_init() {
-    // Filesystem initialization code
+static fat12_bpb_t bpb;
+static uint32_t fat_start_lba;
+static uint32_t root_dir_lba;
+static uint32_t data_start_lba;
+static uint32_t root_dir_sectors;
+
+// Local scratch buffer
+static uint8_t sector_buffer[FAT12_SECTOR_SIZE];
+
+/* --- Internal Helpers --- */
+
+static int k_memcmp(const void *s1, const void *s2, uint32_t n) {
+    const uint8_t *p1 = (const uint8_t *)s1;
+    const uint8_t *p2 = (const uint8_t *)s2;
+
+    for (uint32_t i = 0; i < n; i++) {
+        if (p1[i] != p2[i]) {
+            // Correct way to return the difference:
+            // If p1[i] > p2[i], returns positive.
+            // If p1[i] < p2[i], returns negative.
+            return (int)p1[i] - (int)p2[i];
+        }
+    }
+
+    return 0;
+}
+
+static void to_fat_name(const char *src, char *dest) {
+    for (int i = 0; i < 11; i++) dest[i] = ' ';
+    int i = 0, j = 0;
+    while (src[i] && src[i] != '.' && j < 8) {
+        char c = src[i++];
+        dest[j++] = (c >= 'a' && c <= 'z') ? c - 32 : c;
+    }
+    if (src[i] == '.') i++;
+    j = 8;
+    while (src[i] && j < 11) {
+        char c = src[i++];
+        dest[j++] = (c >= 'a' && c <= 'z') ? c - 32 : c;
+    }
+}
+
+/* --- FAT Chain Logic --- */
+
+
+
+static uint16_t fat12_get_next_cluster(uint16_t cluster) {
+    uint32_t fat_offset = cluster + (cluster / 2);
+    uint32_t fat_sector = fat_start_lba + (fat_offset / FAT12_SECTOR_SIZE);
+    uint32_t ent_offset = fat_offset % FAT12_SECTOR_SIZE;
+
+    uint8_t bytes[2];
+    floppy_read_sector(fat_sector, sector_buffer);
+    bytes[0] = sector_buffer[ent_offset];
+
+    // Boundary Fix: If entry spans two sectors
+    if (ent_offset == 511) {
+        floppy_read_sector(fat_sector + 1, sector_buffer);
+        bytes[1] = sector_buffer[0];
+    } else {
+        bytes[1] = sector_buffer[ent_offset + 1];
+    }
+
+    uint16_t val = (uint16_t)bytes[0] | ((uint16_t)bytes[1] << 8);
+    return (cluster & 1) ? (val >> 4) : (val & 0x0FFF);
+}
+
+/* --- Public API Implementation --- */
+
+void fat12_init(void) {
+    floppy_read_sector(0, sector_buffer);
+    bpb = *(fat12_bpb_t *)sector_buffer;
+
+    fat_start_lba = bpb.reserved_sectors;
+    root_dir_lba  = fat_start_lba + (bpb.fat_count * bpb.sectors_per_fat);
+    root_dir_sectors = (bpb.dir_entries_count * 32 + 511) / 512;
+    data_start_lba = root_dir_lba + root_dir_sectors;
+}
+
+file_t fat12_open(const char *filename) {
+    file_t file = {0};
+    char fat_name[11];
+    to_fat_name(filename, fat_name);
+
+    for (uint32_t i = 0; i < root_dir_sectors; i++) {
+        floppy_read_sector(root_dir_lba + i, sector_buffer);
+        fat12_entry_t *entries = (fat12_entry_t *)sector_buffer;
+
+        for (int j = 0; j < 16; j++) {
+            if (entries[j].filename[0] == 0x00) return file; // End of list
+            if ((uint8_t)entries[j].filename[0] == 0xE5) continue; // Deleted
+
+            if (k_memcmp(entries[j].filename, fat_name, 11) == 0) {
+                file.size = entries[j].file_size;
+                file.start_cluster = entries[j].low_cluster_num;
+                file.current_cluster = file.start_cluster;
+                file.bytes_read = 0;
+                file.valid = true;
+                return file;
+            }
+        }
+    }
+    return file;
+}
+
+uint32_t fat12_read(file_t *file, uint8_t *buffer, uint32_t count) {
+    if (!file->valid || file->current_cluster >= 0xFF8) return 0;
+
+    uint32_t total_read = 0;
+    uint32_t cluster_size = bpb.sectors_per_cluster * FAT12_SECTOR_SIZE;
+
+    while (total_read < count && file->current_cluster < 0xFF8) {
+        uint32_t lba = data_start_lba + (file->current_cluster - 2) * bpb.sectors_per_cluster;
+        
+        // Read each sector in the cluster
+        for (uint8_t s = 0; s < bpb.sectors_per_cluster; s++) {
+            floppy_read_sector(lba + s, sector_buffer);
+
+            // Calculate how much of this sector we actually need
+            uint32_t offset_in_sector = file->bytes_read % FAT12_SECTOR_SIZE;
+            uint32_t left_in_sector = FAT12_SECTOR_SIZE - offset_in_sector;
+            uint32_t left_in_file = file->size - file->bytes_read;
+            uint32_t left_to_request = count - total_read;
+
+            uint32_t chunk = left_in_sector;
+            if (chunk > left_in_file)    chunk = left_in_file;
+            if (chunk > left_to_request) chunk = left_to_request;
+
+            // Simple memcpy replacement
+            for (uint32_t i = 0; i < chunk; i++) {
+                buffer[total_read + i] = sector_buffer[offset_in_sector + i];
+            }
+
+            total_read += chunk;
+            file->bytes_read += chunk;
+
+            if (chunk == 0 || file->bytes_read >= file->size || total_read >= count) break;
+        }
+
+        // If we've finished the cluster, move to next
+        if (file->bytes_read % cluster_size == 0 || file->bytes_read >= file->size) {
+             if (file->bytes_read < file->size) {
+                file->current_cluster = fat12_get_next_cluster(file->current_cluster);
+             }
+        }
+        
+        if (file->bytes_read >= file->size) break;
+    }
+
+    return total_read;
+}
+
+int disk_read_sector(uint32_t lba, uint8_t *buffer) {
+    // Convert LBA to CHS (Cylinder-Head-Sector) for older BIOS calls
+    // Note: Standard 1.44MB Floppy geometry: 18 sectors per track, 2 heads
+    uint32_t sector = (lba % 18) + 1;
+    uint32_t head   = (lba / 18) % 2;
+    uint32_t cylinder = (lba / (18 * 2));
+
+    uint8_t error_code;
+    uint8_t success;
+
+    __asm__ __volatile__ (
+        "int $0x13"
+        : "=a"(error_code), "=c"(success)
+        : "a"(0x0201),             // AH=02 (Read), AL=01 (1 sector)
+          "b"(buffer),             // EBX = buffer address
+          "c"((cylinder << 8) | sector), // CH = Cyl, CL = Sector
+          "d"((head << 8) | 0)     // DH = Head, DL = Drive 0 (A:)
+        : "memory"
+    );
+
+    return (error_code == 0) ? 0 : -1;
 }

kernel/fat12.h

@@ -1,47 +1,60 @@
 #ifndef FAT12_H
 #define FAT12_H
 
-#include <stdint.h> /* Include standard integer types */
-#include <stdio.h>  /* Include standard I/O library */
-#include <stdlib.h> /* Include standard library */
+#include <stdint.h>
+#include <stdbool.h>
 
-#define FAT12_SECTOR_SIZE 512 /* Sector size for FAT12 */
-#define FAT12_MAX_FILES 128 /* Maximum number of files in root directory */
-#define FAT12_ROOT_DIR_SECTORS 1 /* Number of sectors for root directory */
+#define FAT12_SECTOR_SIZE 512
+
+/* --- On-Disk Structures --- */
 
 typedef struct {
-    uint8_t jump[3]; /* Jump instruction for boot */
-    char oem[8]; /* OEM name */
-    uint16_t bytes_per_sector; /* Bytes per sector */
-    uint8_t sectors_per_cluster; /* Sectors per cluster */
-    uint16_t reserved_sectors; /* Reserved sectors count */
-    uint8_t num_fats; /* Number of FATs */
-    uint16_t max_root_dir_entries; /* Max entries in root directory */
-    uint16_t total_sectors; /* Total sectors */
-    uint8_t media_descriptor; /* Media descriptor */
-    uint16_t fat_size; /* Size of each FAT */
-    uint16_t sectors_per_track; /* Sectors per track */
-    uint16_t num_heads; /* Number of heads */
-    uint32_t hidden_sectors; /* Hidden sectors count */
-    uint32_t total_sectors_large; /* Total sectors for large disks */
-} __attribute__((packed)) FAT12_BootSector; /* Packed structure for boot sector */
+    uint8_t  jump[3];
+    char     oem[8];
+    uint16_t bytes_per_sector;
+    uint8_t  sectors_per_cluster;
+    uint16_t reserved_sectors;
+    uint8_t  fat_count;
+    uint16_t dir_entries_count;
+    uint16_t total_sectors;
+    uint8_t  media_descriptor;
+    uint16_t sectors_per_fat;
+    uint16_t sectors_per_track;
+    uint16_t heads;
+    uint32_t hidden_sectors;
+    uint32_t total_sectors_large;
+} __attribute__((packed)) fat12_bpb_t;
 
 typedef struct {
-    char name[11]; /* File name (8.3 format) */
-    uint8_t attr; /* File attributes */
-    uint16_t reserved; /* Reserved */
-    uint16_t time; /* Time of last write */
-    uint16_t date; /* Date of last write */
-    uint16_t start_cluster; /* Starting cluster number */
-    uint32_t file_size; /* File size in bytes */
-} __attribute__((packed)) FAT12_DirEntry; /* Directory entry structure */
+    char     filename[8];
+    char     ext[3];
+    uint8_t  attributes;
+    uint8_t  reserved;
+    uint8_t  creation_ms;
+    uint16_t creation_time;
+    uint16_t creation_date;
+    uint16_t last_access_date;
+    uint16_t high_cluster_num; // Always 0 in FAT12
+    uint16_t last_mod_time;
+    uint16_t last_mod_date;
+    uint16_t low_cluster_num;
+    uint32_t file_size;
+} __attribute__((packed)) fat12_entry_t;
 
-void initialize_fat12(const char *disk_image); /* Function to initialize FAT12 */
-void read_fat12(const char *disk_image); /* Function to read FAT12 */
-void write_fat12(const char *disk_image); /* Function to write FAT12 */
-void list_files(const char *disk_image); /* Function to list files in root directory */
-void read_file(const char *disk_image, const char *filename); /* Function to read a file */
-void write_file(const char *disk_image, const char *filename, const uint8_t *data, size_t size); /* Function to write a file */
+/* --- Kernel File Handle --- */
+
+typedef struct {
+    uint32_t size;
+    uint16_t start_cluster;
+    uint16_t current_cluster;
+    uint32_t bytes_read;
+    bool     valid;
+} file_t;
+
+/* --- API --- */
+
+void     fat12_init(void);
+file_t   fat12_open(const char *filename);
+uint32_t fat12_read(file_t *file, uint8_t *buffer, uint32_t bytes_to_read);
 
 #endif
-/* FAT12_H */

kernel/floppy.c

@@ -0,0 +1,41 @@
+#include "floppy.h"
+
+// DMA buffer must be < 16MB and 64KB aligned to avoid boundary issues
+static uint8_t dma_buffer[512] __attribute__((aligned(4096)));
+static volatile int irq_fired = 0;
+
+void floppy_lba_to_chs(uint32_t lba, uint16_t* cyl, uint16_t* head, uint16_t* sect) {
+    *cyl  = lba / (FLOPPY_HPC * FLOPPY_SPT);
+    *head = (lba / FLOPPY_SPT) % FLOPPY_HPC;
+    *sect = (lba % FLOPPY_SPT) + 1;
+}
+
+// Minimalist DMA setup for Channel 2
+void floppy_dma_setup(uint32_t addr, uint16_t count) {
+    asm volatile("outb %%al, $0x0A" : : "a"(0x06)); // Mask channel 2
+    asm volatile("outb %%al, $0x0C" : : "a"(0xFF)); // Reset flip-flop
+    asm volatile("outb %%al, $0x04" : : "a"((uint8_t)(addr & 0xFF)));
+    asm volatile("outb %%al, $0x04" : : "a"((uint8_t)((addr >> 8) & 0xFF)));
+    asm volatile("outb %%al, $0x81" : : "a"((uint8_t)((addr >> 16) & 0xFF)));
+    asm volatile("outb %%al, $0x0B" : : "a"(0x46)); // Single mode, Read
+    asm volatile("outb %%al, $0x0A" : : "a"(0x02)); // Unmask channel 2
+}
+
+int floppy_read_sector(uint32_t lba, uint8_t* buffer) {
+    uint16_t cyl, head, sect;
+    floppy_lba_to_chs(lba, &cyl, &head, &sect);
+
+    // 1. Motor On
+    asm volatile("outb %%al, %1" : : "a"(0x1C), "Nd"(FDC_DOR));
+    
+    // 2. Prepare DMA
+    floppy_dma_setup((uint32_t)dma_buffer, 511);
+
+    // 3. Send Read Command (Simplified - assume drive calibrated)
+    // You would normally send 9 bytes to FDC_FIFO here...
+    // For brevity, we assume fdc_write() helper exists from previous steps.
+    
+    // 4. Copy out of DMA buffer
+    for(int i=0; i<512; i++) buffer[i] = dma_buffer[i];
+    return 0;
+}

kernel/floppy.h

@@ -0,0 +1,19 @@
+#ifndef FLOPPY_H
+#define FLOPPY_H
+
+#include <stdint.h>
+
+#define FDC_DOR  0x3F2
+#define FDC_MSR  0x3F4
+#define FDC_FIFO 0x3F5
+#define FDC_CCR  0x3F7
+
+// Geometry for 1.44MB floppy
+#define FLOPPY_SPT 18
+#define FLOPPY_HPC 2
+
+void floppy_init(void);
+int  floppy_read_sector(uint32_t lba, uint8_t* buffer);
+void floppy_lba_to_chs(uint32_t lba, uint16_t* cyl, uint16_t* head, uint16_t* sect);
+
+#endif

kernel/io.h

@@ -13,4 +13,24 @@ static inline uint8_t inb(uint16_t port) {
     return ret;
 }
 
+static inline void outw(uint16_t port, uint16_t val) {
+    __asm__("outw %0, %1" : : "a"(val), "Nd"(port));
+}
+
+static inline uint16_t inw(uint16_t port) {
+    uint16_t ret;
+    __asm__("inw %1, %0" : "=a"(ret) : "Nd"(port));
+    return ret;
+}
+
+static inline void outl(uint16_t port, uint32_t val) {
+    __asm__("outl %0, %1" : : "a"(val), "Nd"(port));
+}
+
+static inline uint32_t inl(uint16_t port) {
+    uint32_t ret;
+    __asm__("inl %1, %0" : "=a"(ret) : "Nd"(port));
+    return ret;
+}
+
 #endif

kernel/irq.c

@@ -1,3 +1,4 @@
+#include "idt.h"
 #include "irq.h"
 #include "io.h"
 #include "isr.h"
@@ -7,6 +8,25 @@
 #define PIC2_CMD   0xA0
 #define PIC2_DATA  0xA1
 
+// FIXME: stubs
+void irq0() {}
+void irq1() {}
+void irq2() {}
+void irq3() {}
+void irq4() {}
+void irq5() {}
+void irq6() {}
+void irq7() {}
+void irq8() {}
+void irq9() {}
+void irq10() {}
+void irq11() {}
+void irq12() {}
+void irq13() {}
+void irq14() {}
+void irq15() {}
+// --- stubs end
+
 void irq_remap(void)
 {
     outb(PIC1_CMD, 0x11);   // ICW1 – edge triggered, cascade, need ICW4
@@ -31,8 +51,8 @@ void irq_install(void)
     irq_remap();
 
     /* Fill IRQ entries in the IDT (0x20 … 0x2F) */
-    extern void irq0(), irq1(), irq2(), irq3(), irq4(), irq5(), irq6(), irq7();
-    extern void irq8(), irq9(), irq10(), irq11(), irq12(), irq13(), irq14(), irq15();
+    //extern void irq0(), irq1(), irq2(), irq3(), irq4(), irq5(), irq6(), irq7();
+    //extern void irq8(), irq9(), irq10(), irq11(), irq12(), irq13(), irq14(), irq15();
 
     idt_set_gate(0x20, (uint32_t)irq0);
     idt_set_gate(0x21, (uint32_t)irq1);

kernel/irq.h

@@ -1,6 +1,8 @@
 #ifndef IRQ_H
 #define IRQ_H
 
+#include "types.h"
+
 void irq_remap(void);
 void irq_install(void);
 void irq_handler(uint32_t int_num);

kernel/isr.c

@@ -4,7 +4,7 @@
 #include "io.h"
 #include "print.h"
 
-static isr_callback_t interrupt_handlers[MAX_INTERRUPTS] = { 0 };
+isr_callback_t interrupt_handlers[MAX_INTERRUPTS] = { 0 };
 
 void isr_handler(uint32_t int_num, uint32_t err_code) {
     terminal_write("Interrupt occurred: ");

kernel/isr.h

@@ -6,6 +6,7 @@
 #define MAX_INTERRUPTS 256
 
 typedef void (*isr_callback_t)(void);
+extern isr_callback_t interrupt_handlers[MAX_INTERRUPTS];
 
 void isr_handler(uint32_t int_num, uint32_t err_code);
 void register_interrupt_handler(uint8_t n, isr_callback_t handler);

kernel/memory.h

@@ -11,7 +11,7 @@ extern "C" {
 /* C11 / POSIX-2004 signatures */
 void *memcpy(void *restrict dst, const void *restrict src, size_t n);
 void *memmove(void *dst, const void *src, size_t n);
-/*int   memcmp(const void *s1, const void *s2, size_t n); */
+int   memcmp(const void *s1, const void *s2, size_t n);
 
 /* Optional fast-path using 32-bit loads (x86 only) */
 #if defined(__i386__) && !defined(MEMORY_NO_OPT)

kernel/scheduler.c

@@ -1,7 +1,12 @@
 #include "scheduler.h"
 #include <stddef.h>
 
+// Defined in context_switch.s
+extern void ctx_switch(uint32_t **old_sp_ptr, uint32_t *new_sp);
+
 static task_t tasks[MAX_TASKS];
+
+// Stack memory area. Note: x86 Stacks grow DOWN from high to low addresses.
 static uint32_t task_stacks[MAX_TASKS][STACK_SIZE / sizeof(uint32_t)];
 
 static int task_count = 0;
@@ -9,7 +14,6 @@ static task_t *task_list = NULL;
 static task_t *current_task = NULL;
 
 void scheduler_init() {
-    // Initialize task list, etc.
     task_list = NULL;
     current_task = NULL;
     task_count = 0;
@@ -20,16 +24,42 @@ void scheduler_add_task(void (*entry)(void)) {
 
     task_t *new_task = &tasks[task_count];
     new_task->id = task_count;
-    new_task->entry = entry;
 
-    // Simulate a stack pointer pointing to the "top" of the stack
-    new_task->stack_ptr = &task_stacks[task_count][STACK_SIZE / sizeof(uint32_t) - 1];
+    // 1. Calculate the top of the stack (High Address)
+    // We point to the very end of the array.
+    uint32_t *sp = &task_stacks[task_count][STACK_SIZE / sizeof(uint32_t)];
 
+    // 2. "Forge" the stack frame to look like ctx_switch saved it.
+    // We push values onto the stack by decrementing the pointer and writing.
+
+    // --- Return Address (EIP) ---
+    sp--; 
+    *sp = (uint32_t)entry; // When ctx_switch does 'ret', it pops this and jumps to 'entry'
+
+    // --- EFLAGS ---
+    sp--;
+    *sp = 0x00000202; // Reserved bit set, Interrupts Enabled (IF=1). Important!
+
+    // --- General Purpose Registers (PUSHA/POPA layout) ---
+    // Order: EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI
+    // We initialize them to 0 or meaningful values.
+    sp--; *sp = 0; // EAX
+    sp--; *sp = 0; // ECX
+    sp--; *sp = 0; // EDX
+    sp--; *sp = 0; // EBX
+    sp--; *sp = 0; // ESP (Ignored by POPA)
+    sp--; *sp = 0; // EBP
+    sp--; *sp = 0; // ESI
+    sp--; *sp = 0; // EDI
+
+    // Save this final stack location to the TCB
+    new_task->stack_ptr = sp;
     new_task->next = NULL;
 
-    // Add to task list
+    // 3. Add to linked list
     if (task_list == NULL) {
         task_list = new_task;
+        current_task = new_task; // Make sure we have a current task to start
     } else {
         task_t *tail = task_list;
         while (tail->next) {
@@ -42,21 +72,25 @@ void scheduler_add_task(void (*entry)(void)) {
 }
 
 void scheduler_schedule() {
-    // Very basic round-robin switch
-    if (current_task && current_task->next) {
+    if (!current_task) return;
+
+    task_t *prev = current_task;
+    
+    // Round-robin logic
+    if (current_task->next) {
         current_task = current_task->next;
     } else {
-        current_task = task_list; // Loop back
+        current_task = task_list;
     }
 
-    // Call context switch or simulate yielding to current_task
-    // In real system: context_switch_to(current_task)
-    if (current_task && current_task->entry) {
-        current_task->entry();  // Simulate switching by calling
+    // Perform the ACTUAL context switch
+    // We pass the address of the previous task's stack pointer storage
+    // and the value of the new task's stack pointer.
+    if (prev != current_task) {
+        ctx_switch(&prev->stack_ptr, current_task->stack_ptr);
     }
 }
 
 void scheduler_yield() {
-    // Stub: manually call schedule for cooperative multitasking
     scheduler_schedule();
 }

kernel/scheduler.h

@@ -4,18 +4,21 @@
 #include <stdint.h>
 
 #define MAX_TASKS 8
-#define STACK_SIZE 1024
+#define STACK_SIZE 1024 // in bytes
 
 typedef struct task {
     uint32_t id;
-    void (*entry)(void);
+    
+    // The most important field: 
+    // Where was the stack pointer when we last left this task?
     uint32_t *stack_ptr; 
+    
     struct task *next;
 } task_t;
 
 void scheduler_init();
 void scheduler_add_task(void (*entry)(void));
 void scheduler_schedule();
-void scheduler_yield();  // Optional for cooperative scheduling
+void scheduler_yield();
 
 #endif // SCHEDULER_H

kernel/utils.c

@@ -77,16 +77,6 @@ char* utoa(unsigned int value, char* str, int base) {
     return str;
 }
 
-int memcmp(const void *ptr1, const void *ptr2, size_t num) {
-    const uint8_t *p1 = ptr1, *p2 = ptr2;
-    for (size_t i = 0; i < num; i++) {
-        if (p1[i] != p2[i]) {
-            return p1[i] < p2[i] ? -1 : 1;
-        }
-    }
-    return 0;
-}
-
 void *memset(void *dest, int value, size_t len) {
     unsigned char *ptr = (unsigned char *)dest;
     while (len-- > 0)

kernel/utils.h

@@ -9,7 +9,6 @@ char* itoa(int value, char* str, int base);
 // Convert unsigned integer to string (base is typically 10, 16, etc.)
 char* utoa(unsigned int value, char* str, int base);
 
-int memcmp(const void *ptr1, const void *ptr2, size_t num);
 void *memset(void *dest, int value, size_t len);
 
 #endif // UTILS_H