编译动态链接的内核

我试图在xv6内核中实现KASLR,因此我需要以动态方式重新编译/链接内核(重定位表)。 由于内核当前是硬编码的,即使我更改了内核代码和数据映射,指令仍然会引用硬编码的虚拟地址。我需要一种没有硬编码地址的方法来让指令引用elf的其他部分。这方面的一个例子如下: 这是它在当前编译后的外观示例:

8010018e:   83 ec 0c                sub    $0xc,%esp
80100191:   68 a7 79 10 80          push   $0x801079a7
80100196:   e8 b5 01 00 00          call   80100350 <panic>
8010019b:   90                      nop
8010019c:   8d 74 26 00             lea    0x0(%esi,%eiz,1),%esi.

如您所见,push指令等指令引用了硬编码的v地址($0x801079a7)。这是因为此elf是以静态方式编译的,没有重新定位:(readelf printout)

 Program Headers:
    Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
    LOAD           0x001000 0x80100000 0x00100000 0x0b516 0x15668 RWE 0x1000
    GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RWE 0x10
    Section to Segment mapping:
    Segment Sections...
    00     .text .rodata .stab .stabstr .data .bss
    01
    There is no dynamic section in this file.
    There are no relocations in this file.

我需要关于如何将静态链接的elf二进制文件重新编译为具有重定位的二进制文件,然后能够将内核映射到虚拟内存中的任何位置的建议。此外,为了解析elf以正确地重新定位加载它,我必须在引导加载程序中修改什么?我需要自定义解析内核elf中包含的GOT吗?

下面是一个链接器脚本,用于编译内核并设置其基本硬编码虚拟地址:0x80100000

OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
OUTPUT_ARCH(i386)
ENTRY(_start)

SECTIONS
{
    /* Link the kernel at this address: "." means the current address */
        /* Must be equal to KERNLINK */
    . = 0x80100000;

    .text : AT(0x100000) {
        *(.text .stub .text.* .gnu.linkonce.t.*)
    }

    PROVIDE(etext = .); /* Define the 'etext' symbol to this value */

    .rodata : {
        *(.rodata .rodata.* .gnu.linkonce.r.*)
    }

    /* Include debugging information in kernel memory */
    .stab : {
        PROVIDE(__STAB_BEGIN__ = .);
        *(.stab);
        PROVIDE(__STAB_END__ = .);
        BYTE(0)     /* Force the linker to allocate space
                   for this section */
    }

    .stabstr : {
        PROVIDE(__STABSTR_BEGIN__ = .);
        *(.stabstr);
        PROVIDE(__STABSTR_END__ = .);
        BYTE(0)     /* Force the linker to allocate space
                   for this section */
    }

    /* Adjust the address for the data segment to the next page */
    . = ALIGN(0x1000);

    /* Conventionally, Unix linkers provide pseudo-symbols
     * etext, edata, and end, at the end of the text, data, and bss.
     * For the kernel mapping, we need the address at the beginning
     * of the data section, but that's not one of the conventional
     * symbols, because the convention started before there was a
     * read-only rodata section between text and data. */
    PROVIDE(data = .);

    /* The data segment */
    .data : {
        *(.data)
    }

    PROVIDE(edata = .);

    .bss : {
        *(.bss)
    }

    PROVIDE(end = .);

    /DISCARD/ : {
        *(.eh_frame .note.GNU-stack)
    }
}