失敗に終わったプロジェクト：楽しくなかった春節の7日間

    .section .text.entry
    .globl _start
    # 仅仅是设置了 sp 就跳转到 main
_start:
    la sp, bootstacktop
    call bootmain

# 启动线程的内核栈 bootstack 放置在 bss 段的 stack 标记处
    .section .bss.stack
    .align 12
    .global bootstack
bootstack:
    # 以下 16K 字节的空间作为 OS 的启动栈
    .space 0x4000
    .global bootstacktop
bootstacktop:

    .section .data
    .globl _binary_kernel_elf_start
    .globl _binary_kernel_elf_end
_binary_kernel_elf_start:
    .incbin "kernel.elf"
_binary_kernel_elf_end:

void
bootmain()
{
    struct elfhdr *elf;
    struct proghdr *ph, *eph;
    void (*entry)(void);
    uchar *pa;
 
    elf = (struct elfhdr *)(_binary_kernel_elf_start);
 
    if (elf->magic != ELF_MAGIC)
        return;
 
    ph = (struct proghdr *)((uchar *)elf + elf->phoff);
    eph = ph + elf->phnum;
    for (; ph < eph; ph++)
    {
        pa = (uchar *)ph->paddr;
        readseg(pa, ph->filesz, ph->off);
        if (ph->memsz > ph->filesz)
            clearMem(pa + ph->filesz, ph->memsz - ph->filesz);
    }
 
    entry = (void (*)(void))(elf->entry);
    entry();
}

#include "textflag.h"

TEXT ·rt0(SB),NOSPLIT|NOFRAME,$0
    CALL ·kernelStackTop(SB)
    MOV  0(SP), A1
    MOV  A1, SP
    CALL ·kmain(SB)
    UNDEF
    RET

type stack [16 * 4096]byte

type virtualAddress uintptr

var (
    kstack stack
)

//go:nosplit
func (s *stack) top() virtualAddress {
    stackTop := uintptr(unsafe.Pointer(&s[0])) + unsafe.Sizeof(*s)
    // Align to 16 bytes.
    stackTop = stackTop &^ 0xf
    return virtualAddress(stackTop)
}

//go:nosplit
func kernelStackTop() uint64 {
    return uint64(kstack.top())
}

//go:nosplit
func rt0()

//go:nosplit
func kmain() {
    for {
    }
}

Image: kernel.elf
    $(CC) $(CFLAGS) -fno-pic -O -nostdinc -I. -c boot/boot.c
    $(CC) $(CFLAGS) -fno-pic -nostdinc -I. -c boot/boot_header.S
    $(LD) $(LDFLAGS) -T image.ld -o Image boot.o boot_header.o

kernel.elf:
    GOOS=linux GOARCH=riscv64 go build -o kernel.elf -ldflags '-E goose/kernel.rt0 -T 0x80200000' -gcflags "-N -l" ./kmain

/* 执行入口 */
ENTRY(_start)

/* 数据存放起始地址 */
BASE_ADDRESS = 0x80000000;

SECTIONS
{
    /* . 表示当前地址（location counter） */
    . = BASE_ADDRESS;

    /* start 符号表示全部的开始位置 */
    kernel_start = .;

    text_start = .;

    /* .text 字段 */
    .text : {
        /* 把 entry 函数放在最前面 */
        *(.text.entry)
        /* 要链接的文件的 .text 字段集中放在这里 */
        *(.text .text.*)
    }
    ...
}

Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x00000000801ff040 0x00000000801ff040
                 0x0000000000000188 0x0000000000000188  R      0x10000
  NOTE           0x0000000000000f9c 0x00000000801fff9c 0x00000000801fff9c
                 0x0000000000000064 0x0000000000000064  R      0x4
  LOAD           0xffffffffffff1000 0x00000000801f0000 0x00000000801f0000
                 0x0000000000063300 0x0000000000063300  R E    0x10000
  LOAD           0x0000000000060000 0x0000000080260000 0x0000000080260000
                 0x000000000006adb8 0x000000000006adb8  R      0x10000
  ...