启动期间生成的ELF可执行段错误 [英] Generated ELF executable segfaults during startup

问题描述

我正在生成一个ELF可执行文件，并将.text节加载到LOAD段中.它可以很好地反汇编，但是尝试在 gdb 下运行它会给出在启动程序期间因信号SIGSEGV终止，出现分段错误.

I'm generating an ELF executable with a .text section loaded into a LOAD segment. It disassembles fine, but trying to run it under gdb gives During startup program terminated with signal SIGSEGV, Segmentation fault.

readelf 给出:

ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x400056
  Start of program headers:          759 (bytes into file)
  Start of section headers:          503 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         1
  Size of section headers:           64 (bytes)
  Number of section headers:         4
  Section header string table index: 2

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .text             PROGBITS         0000000000400040  00000040
       000000000000005b  0000000000000000  AX       0     0     16
  [ 2] .strtab           STRTAB           0000000000000000  0000009b
       000000000000009c  0000000000000000           0     0     4
  [ 3] .symtab           SYMTAB           0000000000000000  00000137
       00000000000000c0  0000000000000018           2     1     4
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
  I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
  O (extra OS processing required) o (OS specific), p (processor specific)

There are no section groups in this file.

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000040 0x0000000000400000 0x0000000000400000
                 0x000000000000009b 0x000000000000009b  R E    200000

 Section to Segment mapping:
  Segment Sections...
   00     .text 

There is no dynamic section in this file.

There are no relocations in this file.

The decoding of unwind sections for machine type Advanced Micro Devices X86-64 is not currently supported.

Symbol table '.symtab' contains 8 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 0000000000000000     0 FUNC    GLOBAL DEFAULT    1 
     2: 0000000000400040    16 FUNC    GLOBAL DEFAULT    1 _R_Potato
     3: 0000000000400050     6 FUNC    GLOBAL DEFAULT    1 _R_Main
     4: 0000000000000000     0 SECTION LOCAL  DEFAULT    1 
     5: 0000000000400056    18 FUNC    GLOBAL DEFAULT    1 _start
     6: 0000000000400068    25 FUNC    GLOBAL DEFAULT    1 GetStringLength
     7: 0000000000400081    26 FUNC    GLOBAL DEFAULT    1 _R_Print

如果需要，可以在此处中找到十六进制转储.我假设问题出在内核试图映射LOAD段中的内容，但是我没有看到问题.这是怎么回事?

The hexdump, if needed, can be found here. I'm assuming the problem is with the kernel trying to mmap the stuff from the LOAD segment, but I'm failing to see a problem. What's going on here?

推荐答案

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000040 0x0000000000400000 0x0000000000400000
                 0x000000000000009b 0x000000000000009b  R E    200000

这是您的问题所在:您正在要求内核执行等效的 mmap(0x400000、0x9b，PROT_READ | PROT_EXEC，MAP_FIXED，$ fd，0x40)，但是这样的mmap 调用始终会失败，并显示 EINVAL ，因为地址和偏移量不是等效的模对齐方式.

This is your problem right there: you are asking the kernel to perform an equivalent of mmap(0x400000, 0x9b, PROT_READ|PROT_EXEC, MAP_FIXED, $fd, 0x40), but such mmap call will always fail with EINVAL because the address and offset are not equivalent modulo alignment.

您希望文件偏移量为 0 ，而不是 0x40 .也就是说，您的 LOAD 段应该同时覆盖 和 Elf64_Ehdr 和程序 .text (您的 LOAD 段的大小已经包括了两者).

You want file offset to be 0, not 0x40. That is, your LOAD segment should cover both the Elf64_Ehdr and program .text together (the size of your LOAD segment already includes both).

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