c - 如何在内存复制功能到用户空间后更正相对寻址？

Question

您好，我正在尝试使用“sysexit”从内核级跳转到用户级，并准备了以下用户函数:

void user_level_function(void)
{
    color_printk(RED, BLACK, "user_level_function task is running\n");
    while(1);
}

但是 GCC 编译如下:

ffff80000010322f <user_level_function>:
ffff80000010322f:   55                      push   %rbp
ffff800000103230:   48 89 e5                mov    %rsp,%rbp
ffff800000103233:   41 57                   push   %r15
ffff800000103235:   48 83 ec 08             sub    $0x8,%rsp
ffff800000103239:   48 8d 0d f9 ff ff ff    lea    -0x7(%rip),%rcx        # ffff800000103239 <user_level_function+0xa>
ffff800000103240:   49 bb af d9 00 00 00    movabs $0xd9af,%r11
ffff800000103247:   00 00 00 
ffff80000010324a:   4c 01 d9                add    %r11,%rcx
ffff80000010324d:   48 b8 a0 01 00 00 00    movabs $0x1a0,%rax
ffff800000103254:   00 00 00 
ffff800000103257:   48 8d 14 01             lea    (%rcx,%rax,1),%rdx
ffff80000010325b:   be 00 00 00 00          mov    $0x0,%esi
ffff800000103260:   bf 00 00 ff 00          mov    $0xff0000,%edi
ffff800000103265:   49 89 cf                mov    %rcx,%r15
ffff800000103268:   b8 00 00 00 00          mov    $0x0,%eax
ffff80000010326d:   49 b8 ca 4a ff ff ff    movabs $0xffffffffffff4aca,%r8
ffff800000103274:   ff ff ff 
ffff800000103277:   49 01 c8                add    %rcx,%r8
ffff80000010327a:   41 ff d0                callq  *%r8
ffff80000010327d:   eb fe                   jmp    ffff80000010327d <user_level_function+0x4e>

上面的汇编代码表明该函数正在使用其当前编译地址进行寻址。

因此我内存copy函数到用户空间(0x800000)执行后，由于相对寻址，寻址困惑。

unsigned long do_execve(void)
{
    color_printk(RED,BLACK,"do_execve task is running\n");
    memcpy(user_level_function,(void *)0x800000,1024);
    PUSH_ALL;
    __asm__ __volatile__ (
        "wrmsr  \n\t"
        "movq $0x800000, %%rdx \n\t"
        "movq $0xa00000, %%rcx \n\t"
        ".byte  0x48    \n\t"
        "sysexit        \n\t"
        :
        :"d"((unsigned long)KERNEL_CS >> 32),
         "a"((unsigned long)KERNEL_CS & 0xffffffff),
         "c"(0x174)
        :"memory"
    );
    POP_ALL;
    return 0;
}

所以想请问有没有办法解决？

非常感谢!!

Answer 1

-fno-pic 编译器选项可以是您想要的吗？