Initial Commit

Makefile

@@ -0,0 +1,56 @@
+# Toolchain
+CC = riscv64-unknown-elf-gcc
+LD = riscv64-unknown-elf-ld
+
+# Directories
+SRC_DIR = src
+BUILD_DIR = build
+OUTPUT_DIR = output
+
+# Flags
+# Added -O0 for easier debugging and -g for symbols
+CFLAGS = -Wall -Wextra -ffreestanding -nostdlib -mcmodel=medany -Iinclude -O0 -g
+LDFLAGS = -T linker.ld
+
+# 1. Find sources
+SRCS_C = $(shell find $(SRC_DIR) -name "*.c")
+SRCS_S = $(shell find $(SRC_DIR) -name "*.S")
+
+# 2. Object mapping
+OBJS_C = $(patsubst $(SRC_DIR)/%.c, $(BUILD_DIR)/%.o, $(SRCS_C))
+OBJS_S = $(patsubst $(SRC_DIR)/%.S, $(BUILD_DIR)/%.o, $(SRCS_S))
+# Put Assembly first to help the linker find _start
+OBJS   = $(OBJS_S) $(OBJS_C)
+
+# 3. List of all required build subdirectories
+OBJ_DIRS = $(sort $(dir $(OBJS)))
+
+TARGET = $(OUTPUT_DIR)/kernel.elf
+
+.PHONY: all clean run
+
+all: $(TARGET)
+
+# The final link step
+# Added -Wl, to pass LDFLAGS to the actual linker
+$(TARGET): $(OBJS) | $(OUTPUT_DIR)
+	$(CC) $(CFLAGS) -Wl,$(LDFLAGS) $(OBJS) -o $(TARGET)
+
+# Rule for C files
+$(BUILD_DIR)/%.o: $(SRC_DIR)/%.c | $(OBJ_DIRS)
+	$(CC) $(CFLAGS) -c $< -o $@
+
+# Rule for Assembly files
+$(BUILD_DIR)/%.o: $(SRC_DIR)/%.S | $(OBJ_DIRS)
+	$(CC) $(CFLAGS) -c $< -o $@
+
+# Create directories using order-only prerequisites (|)
+$(OBJ_DIRS) $(OUTPUT_DIR):
+	mkdir -p $@
+
+run: all
+	clear
+	qemu-system-riscv64 -M virt -bios none -kernel $(TARGET) -nographic
+
+clean:
+	rm -rf $(BUILD_DIR) $(OUTPUT_DIR)

linker.ld

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+ENTRY(_start)
+
+SECTIONS
+{
+    . = 0x80000000;
+
+    .text : ALIGN(4K) {
+        /* This matches the .section .text.boot in your assembly */
+        *(.text.boot) 
+        *(.text .text.*)
+    }
+
+    .rodata : ALIGN(4K) {
+        *(.rodata .rodata.*)
+    }
+
+    .data : ALIGN(4K) {
+        *(.data .data.*)
+    }
+
+    .bss : ALIGN(4K) {
+        PROVIDE(_bss_start = .);
+        *(.bss .bss.*)
+        *(COMMON)
+        PROVIDE(_bss_end = .);
+    }
+
+    /* Keep the stack at the very end to prevent it from overwriting code if it overflows */
+    . = ALIGN(16);
+    PROVIDE(_stack_bottom = .);
+    . += 4096; 
+    PROVIDE(stack_top = .);
+}

src/boot/entry.S

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+.section .text
+.global _start
+_start:
+    la sp, stack_top      # Set up the stack pointer
+    call kmain            # Jump to our C code
+loop:
+    wfi                   # Wait for Interrupt (saves CPU)
+    j loop                # Infinite loop if C returns
+
+.section .bss
+.align 16
+stack_low:
+    .skip 4096            # 4KB of stack space
+stack_top:

src/kernel/kernel.c

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+#include <stdint.h>
+#include <stddef.h>
+
+void kmain() {
+    char *uart = (char *)0x10000000;
+    char *msg = "Hello, OS World!\n";
+    
+    for (int i = 0; msg[i] != '\0'; i++) {
+        *uart = msg[i]; // Write each character to the UART
+    }
+}