build: replace hosted target with static linux and add kernel target

Co-authored-by: aider (openrouter/moonshotai/kimi-k2.6) <aider@aider.chat>

Makefile

@@ -2,21 +2,22 @@ CC = clang
 CFLAGS = -Wall -Wextra -g -std=c11
 COMMON_SRCS = forth_core.c forth_dict.c forth_words.c forth_interp.c main.c
 
-HOSTED_SRCS = $(COMMON_SRCS) platform_hosted.c
+LINUX_SRCS = $(COMMON_SRCS) platform_linux.c
-FREESTANDING_SRCS = $(COMMON_SRCS) platform_freestanding.c
+KERNEL_SRCS = $(COMMON_SRCS) platform_kernel.c kernel_entry.S
+KERNEL_LD = kernel.ld
 
 TARGET = forth
-FREESTANDING_TARGET = forth_freestanding
+KERNEL_TARGET = forth.kernel
 
 all: $(TARGET)
 
-$(TARGET): $(HOSTED_SRCS) forth.h
+$(TARGET): $(LINUX_SRCS) forth.h
-	$(CC) $(CFLAGS) -D_POSIX_C_SOURCE=200809L -o $@ $(HOSTED_SRCS)
+	$(CC) $(CFLAGS) -static -nostdlib -ffreestanding -fno-stack-protector -o $@ $(LINUX_SRCS)
 
-$(FREESTANDING_TARGET): $(FREESTANDING_SRCS) forth.h
+$(KERNEL_TARGET): $(KERNEL_SRCS) forth.h $(KERNEL_LD)
-	$(CC) $(CFLAGS) -ffreestanding -nostdlib -fno-stack-protector -o $@ $(FREESTANDING_SRCS)
+	$(CC) $(CFLAGS) -ffreestanding -nostdlib -fno-stack-protector -mno-red-zone -o $@ $(KERNEL_SRCS) -T$(KERNEL_LD) -Wl,--build-id=none
 
 clean:
-	rm -f $(TARGET) $(FREESTANDING_TARGET)
+	rm -f $(TARGET) $(KERNEL_TARGET)
 
 .PHONY: all clean

kernel.ld

@@ -0,0 +1,30 @@
+ENTRY(_start)
+
+SECTIONS
+{
+    . = 0x100000;
+
+    .text : ALIGN(4K)
+    {
+        *(.multiboot2)
+        *(.text)
+    }
+
+    .rodata : ALIGN(4K)
+    {
+        *(.rodata)
+    }
+
+    .data : ALIGN(4K)
+    {
+        *(.data)
+    }
+
+    .bss : ALIGN(4K)
+    {
+        __bss_start = .;
+        *(.bss)
+        *(COMMON)
+        __bss_end = .;
+    }
+}

kernel_entry.S

@@ -0,0 +1,98 @@
+# Multiboot2 header and x86_64 long-mode bootstrap
+
+.section .multiboot2, "a"
+.align 8
+multiboot_header:
+    .long 0xe85250d6
+    .long 0
+    .long multiboot_header_end - multiboot_header
+    .long -(0xe85250d6 + 0 + (multiboot_header_end - multiboot_header))
+
+    .align 8
+    .word 0
+    .word 0
+    .long 8
+multiboot_header_end:
+
+.section .bss, "aw", @nobits
+.align 4096
+pml4:
+    .space 4096
+pdpt:
+    .space 4096
+pd:
+    .space 4096
+
+.align 16
+stack_bottom:
+    .space 16384
+stack_top:
+
+.section .text
+.code32
+.global _start
+.type _start, @function
+_start:
+    movl $stack_top, %esp
+
+    movl $pdpt, %eax
+    orl $0x03, %eax
+    movl %eax, pml4
+
+    movl $pd, %eax
+    orl $0x03, %eax
+    movl %eax, pdpt
+
+    movl $0x00000083, %eax
+    movl $pd, %edi
+    movl $512, %ecx
+1:
+    movl %eax, (%edi)
+    addl $0x200000, %eax
+    addl $8, %edi
+    loop 1b
+
+    movl $pml4, %eax
+    movl %eax, %cr3
+
+    movl %cr4, %eax
+    orl $0x20, %eax
+    movl %eax, %cr4
+
+    movl $0xC0000080, %ecx
+    rdmsr
+    orl $0x100, %eax
+    wrmsr
+
+    movl %cr0, %eax
+    orl $0x80000000, %eax
+    movl %eax, %cr0
+
+    lgdt gdt64_pointer
+    ljmp $0x08, $long_mode_start
+
+.code64
+long_mode_start:
+    movabsq $stack_top, %rax
+    movq %rax, %rsp
+
+    movabsq $__bss_start, %rdi
+    movabsq $__bss_end, %rcx
+    subq %rdi, %rcx
+    xorq %rax, %rax
+    rep stosb
+
+    call kernel_main
+    cli
+1:
+    hlt
+    jmp 1b
+
+.section .rodata
+.align 8
+gdt64:
+    .quad 0x0000000000000000
+    .quad 0x00209A0000000000
+gdt64_pointer:
+    .word gdt64_pointer - gdt64 - 1
+    .quad gdt64

platform_kernel.c

@@ -0,0 +1,142 @@
+#include "forth.h"
+#include <stdint.h>
+#include <stdarg.h>
+
+// VGA text-mode buffer
+static uint16_t* vga_buffer = (uint16_t*)0xB8000;
+static int vga_row = 0;
+static int vga_col = 0;
+
+static void vga_putchar(char c) {
+    if (c == '\n') {
+        vga_col = 0;
+        vga_row++;
+    } else {
+        int idx = vga_row * 80 + vga_col;
+        vga_buffer[idx] = (uint16_t)((0x0F << 8) | (unsigned char)c);
+        vga_col++;
+        if (vga_col >= 80) {
+            vga_col = 0;
+            vga_row++;
+        }
+    }
+    if (vga_row >= 25) {
+        vga_row = 0;
+        vga_col = 0;
+    }
+}
+
+static inline void outb(uint16_t port, uint8_t val) {
+    __asm__ volatile ("outb %0, %1" : : "a"(val), "Nd"(port));
+}
+
+static inline uint8_t inb(uint16_t port) {
+    uint8_t ret;
+    __asm__ volatile ("inb %1, %0" : "=a"(ret) : "Nd"(port));
+    return ret;
+}
+
+static void serial_init(void) {
+    outb(0x3F8 + 1, 0x00);
+    outb(0x3F8 + 3, 0x80);
+    outb(0x3F8 + 0, 0x01);
+    outb(0x3F8 + 1, 0x00);
+    outb(0x3F8 + 3, 0x03);
+    outb(0x3F8 + 2, 0xC7);
+    outb(0x3F8 + 4, 0x0B);
+}
+
+void forth_putchar(char c) {
+    vga_putchar(c);
+    while ((inb(0x3F8 + 5) & 0x20) == 0) { }
+    outb(0x3F8, (uint8_t)c);
+}
+
+int forth_getchar(void) {
+    if ((inb(0x3F8 + 5) & 1) == 0) {
+        return FORTH_EOF;
+    }
+    return inb(0x3F8);
+}
+
+void forth_fflush(void) {
+}
+
+void forth_panic(void) {
+    __asm__ volatile ("cli; hlt");
+    __builtin_unreachable();
+}
+
+int64_t forth_strtoll(const char* str, char** endptr, int base) {
+    const char* s = str;
+    int neg = 0;
+    int64_t val = 0;
+    while (forth_isspace(*s)) s++;
+    if (*s == '-') { neg = 1; s++; }
+    else if (*s == '+') { s++; }
+    while (*s >= '0' && *s <= '9') {
+        val = val * base + (*s - '0');
+        s++;
+    }
+    if (endptr) *endptr = (char*)s;
+    return neg ? -val : val;
+}
+
+static void print_str(const char* s) {
+    while (*s) forth_putchar(*s++);
+}
+
+static void print_int(long long v) {
+    char buf[32];
+    int i = 30;
+    int neg = 0;
+    if (v < 0) { neg = 1; v = -v; }
+    buf[31] = '\0';
+    if (v == 0) {
+        buf[i--] = '0';
+    } else {
+        while (v > 0 && i >= 0) {
+            buf[i--] = '0' + (v % 10);
+            v /= 10;
+        }
+    }
+    if (neg) buf[i--] = '-';
+    print_str(&buf[i + 1]);
+}
+
+void forth_printf(const char* fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    while (*fmt) {
+        if (*fmt == '%' && *(fmt + 1)) {
+            fmt++;
+            if (*fmt == 's') {
+                print_str(va_arg(ap, const char*));
+            } else if (*fmt == 'c') {
+                forth_putchar((char)va_arg(ap, int));
+            } else if (*fmt == '%') {
+                forth_putchar('%');
+            } else if (*fmt == 'l') {
+                if (*(fmt + 1) == 'l' && (*(fmt + 2) == 'd' || *(fmt + 2) == 'i' || *(fmt + 2) == 'u')) {
+                    fmt += 2;
+                    print_int(va_arg(ap, long long));
+                }
+            } else if (*fmt == 'd' || *fmt == 'i' || *fmt == 'u') {
+                print_int(va_arg(ap, int));
+            } else {
+                forth_putchar('%');
+                forth_putchar(*fmt);
+            }
+        } else {
+            forth_putchar(*fmt);
+        }
+        fmt++;
+    }
+    va_end(ap);
+}
+
+void kernel_main(void) {
+    serial_init();
+    forth_run();
+    forth_panic();
+}