Hello world

LICENSE

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+/*
+ * ----------------------------------------------------------------------------
+ * "THE BEER-WARE LICENSE" (Revision 42):
+ * <phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
+ * can do whatever you want with this stuff. If we meet some day, and you think
+ * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
+ * ----------------------------------------------------------------------------
+ */

src/.clang-format

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+BasedOnStyle: LLVM
+IndentWidth: 4
+ColumnLimit: 80

src/.clangd

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+CompileFlags:
+  Add: [-std=c11, -Wall, -Wextra, --target=riscv32, -ffreestanding, -nostdlib]

src/.gitignore

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+/disk/*
+!/disk/.gitkeep
+*.map
+*.tar
+*.o
+*.elf
+*.bin
+*.log
+*.pcap

src/Makefile

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+CC = clang
+CFLAGS = -std=c11 -O2 -g3 -Wall -Wextra --target=riscv32 -ffreestanding -nostdlib
+
+kernel:
+	$(CC) $(CFLAGS) -Wl,-Tkernel.ld -Wl,-Map=kernel.map -o kernel.elf kernel.c common.c

src/common.c

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+#include "common.h"
+
+void putchar(char ch);
+
+void *memset(void *buf, char c, size_t n) {
+    uint8_t *p = (uint8_t *)buf;
+    while (n--)
+        *p++ = c;
+    return buf;
+}
+
+void *memcpy(void *dst, const void *src, size_t n) {
+    uint8_t *d = (uint8_t *)dst;
+    const uint8_t *s = (const uint8_t *)src;
+    while (n--)
+        *d++ = *s++;
+    return dst;
+}
+
+char *strcpy(char *dst, const char *src) {
+    char *d = dst;
+    while (*src)
+        *d++ = *src++;
+    *d = '\0';
+    return dst;
+}
+
+int strcmp(const char *s1, const char *s2) {
+    while (*s1 && *s2) {
+        if (*s1 != *s2)
+            break;
+        s1++;
+        s2++;
+    }
+
+    return *(unsigned char *)s1 - *(unsigned char *)s2;
+}
+
+void printf(const char *fmt, ...) {
+    va_list vargs;
+    va_start(vargs, fmt);
+
+    while (*fmt) {
+        if (*fmt == '%') {
+            fmt++;
+            switch (*fmt) {
+            case '\0':
+                putchar('%');
+                goto end;
+            case '%':
+                putchar('%');
+                break;
+            case 's': {
+                const char *s = va_arg(vargs, const char *);
+                while (*s) {
+                    putchar(*s);
+                    s++;
+                }
+                break;
+            }
+            case 'd': {
+                int value = va_arg(vargs, int);
+                if (value < 0) {
+                    putchar('-');
+                    value = -value;
+                }
+
+                int divisor = 1;
+                while (value / divisor > 9)
+                    divisor *= 10;
+
+                while (divisor > 0) {
+                    putchar('0' + value / divisor);
+                    value %= divisor;
+                    divisor /= 10;
+                }
+
+                break;
+            }
+            case 'x': {
+                int value = va_arg(vargs, int);
+                for (int i = 7; i >= 0; i--) {
+                    int nibble = (value >> (i * 4)) & 0xf;
+                    putchar("0123456789abcdef"[nibble]);
+                }
+            }
+            }
+        } else {
+            putchar(*fmt);
+        }
+
+        fmt++;
+    }
+
+end:
+    va_end(vargs);
+}

src/common.h

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+#pragma once
+
+typedef int bool;
+
+typedef unsigned char uint8_t;
+typedef unsigned short uint16_t;
+typedef unsigned int uint32_t;
+typedef unsigned long long uint64_t;
+
+typedef uint32_t size_t;
+typedef uint32_t paddr_t;
+typedef uint32_t vaddr_t;
+
+#define true 1
+#define false 0
+
+#define NULL ((void *)0)
+
+#define align_up(value, align) __builtin_align_up(value, align)
+#define is_aligned(value, align) __builtin_is_aligned(value, align)
+
+#define offsetof(type, member) __builtin_offsetof(type, member)
+
+#define va_list __builtin_va_list
+#define va_start __builtin_va_start
+#define va_end __builtin_va_end
+#define va_arg __builtin_va_arg
+
+void *memset(void *buf, char c, size_t n);
+void *memcpy(void *dst, const void *src, size_t n);
+
+char *strcpy(char *dst, const char *src);
+int strcmp(const char *s1, const char *s2);
+
+void printf(const char *fmt, ...);

src/kernel.c

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+#include "kernel.h"
+
+struct sbiret sbi_call(long arg0, long arg1, long arg2, long arg3, long arg4,
+                       long arg5, long fid, long eid) {
+    register long a0 __asm__("a0") = arg0;
+    register long a1 __asm__("a1") = arg1;
+    register long a2 __asm__("a2") = arg2;
+    register long a3 __asm__("a3") = arg3;
+    register long a4 __asm__("a4") = arg4;
+    register long a5 __asm__("a5") = arg5;
+    register long a6 __asm__("a6") = fid;
+    register long a7 __asm__("a7") = eid;
+
+    __asm__ __volatile__("ecall"
+                         : "=r"(a0), "=r"(a1)
+                         : "r"(a0), "r"(a1), "r"(a2), "r"(a3), "r"(a4), "r"(a5),
+                           "r"(a6), "r"(a7)
+                         : "memory");
+    return (struct sbiret){.error = a0, .value = a1};
+}
+
+void putchar(char ch) { sbi_call(ch, 0, 0, 0, 0, 0, 0, 1); }
+
+void kernel_main(void) {
+    memset(__bss, 0, (size_t)__bss_end - (size_t)__bss);
+
+    PANIC("booted!");
+    printf("unreachable here!\n");
+}
+
+__attribute__((section(".text.boot"))) __attribute__((naked)) void boot(void) {
+    __asm__ __volatile__("mv sp, %[stack_top]\n"
+                         "j kernel_main\n"
+                         :
+                         : [stack_top] "r"(__stack_top));
+}

src/kernel.h

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+#pragma once
+
+#include "common.h"
+
+extern char __bss[], __bss_end[], __stack_top[];
+
+struct sbiret {
+    long error;
+    long value;
+};
+
+#define PANIC(fmt, ...)                                                        \
+    do {                                                                       \
+        printf("PANIC: %s:%d: " fmt "\n", __FILE__, __LINE__, ##__VA_ARGS__);  \
+        while (1) {                                                            \
+        }                                                                      \
+    } while (0)

src/kernel.ld

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+ENTRY(boot)
+
+SECTIONS {
+    . = 0x80200000;
+
+    .text :{
+        KEEP(*(.text.boot));
+        *(.text .text.*);
+    }
+
+    .rodata : ALIGN(4) {
+        *(.rodata .rodata.*);
+    }
+
+    .data : ALIGN(4) {
+        *(.data .data.*);
+    }
+
+    .bss : ALIGN(4) {
+        __bss = .;
+        *(.bss .bss.* .sbss .sbss.*);
+        __bss_end = .;
+    }
+
+    . = ALIGN(4);
+    . += 128 * 1024; /* 128KB */
+    __stack_top = .;
+}

src/run.bat

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+@echo off
+make kernel
+cd /d "C:\Program Files\qemu"
+qemu-system-riscv32.exe -machine virt -bios default -nographic -serial mon:stdio --no-reboot -kernel %~dp0kernel.elf

src/run.sh

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+#!/bin/bash
+set -xue
+
+qemu-system-riscv32 -machine virt -bios default -nographic -serial mon:stdio --no-reboot -kernel kernel.elf