为什么自定义 init 在自定义 linux 系统上失败并显示错误代码 -8？

Question

I'm building a custom init for a linux system (for a thin client) (currently emulated over qemu). I'm compiling my executable with:

$ gcc -fpic -static -nostdlib init.c -o init

For some reason when this executable is put over /bin/, system refuses to boot and spits out a error code that is extremely unhelpful (-8). Based on some googling this seems to be corresponding to a signal 8 which is SIGFPE, but oddly enough nothing related to impossible mathematics like dividing by zero happens at any place in the code or in the complicated assembly examined. The source code doesn't matter at all, any source fails to build but here is a example that fails.

size_t strlen(const char* s) {
    for(unsigned i = 0; ; ++i) if(s[i] == 0) return i;
}
void puts(char* s) {
    asm("mov %0, %%r11" :: "r"(s));
    asm("mov %0, %%r14" :: "r"(strlen(s)));
    asm("mov $1, %rax\n"
        "mov  %r11, %rsi\n"
        "mov %r14, %rdx\n"
        "mov $1, %rdi\n"
        "syscall");
}
int _start() {
    puts("test");






    asm volatile(
        "mov $60, %rax\n"
        "push %r11\n"
        "mov %r11, %rdi\n"
        "pop %r11\n"
        "syscall"
    );
    return 0;
}

Run /bin/init as init process
Kernel panic - not syncing: Requested init /bin/init failed (error -8).

Kernel Offset: disabled

Answer 1

This issue happens if you forgot to toggle 64 bit kernel in configuration before compiling the kernel it may also caused by using a wrong compiler such as a compiler that isn't for Linux but rather was made to produce elf executable for other unixes. Code uses 64 bit registers while kernel is only 32 bit.

Another cause could be due a badly made initramfs. I had trouble with cpio files until I read the manual which is extremely helpful:

Using the initial RAM disk (initrd)

While not related also do not use exit syscall on init process well because Init is supposed to be run until system shuts down and exiting init will result in a kernel panic.