x86_64环境nasm+ld编译最简汇编程序运行段错误问题排查

问题复现 #

编写仅实现进程退出功能的极简汇编程序：

SECTION .TEXT
        GLOBAL _start

_start:
        mov rax, 60
        mov rdi, 0
        syscall

执行以下命令编译链接生成64位ELF可执行文件：

nasm -f elf64 -o test.o test.asm
ld -o test test.o

运行生成的可执行文件直接触发段错误：

./test
Segmentation fault (core dumped)

初步排查 #

• 网上同逻辑汇编示例可正常运行，初步判断问题出在编译/链接参数环节
• 使用readelf -a test查看ELF结构，未发现直观异常，输出如下：

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:               0x401000
  Start of program headers:          64 (bytes into file)
  Start of section headers:          4352 (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:         5
  Section header string table index: 4

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         0000000000401000  00001000
       000000000000000c  0000000000000000   A       0     0     1
  [ 2] .symtab           SYMTAB           0000000000000000  00001010
       00000000000000a8  0000000000000018           3     3     8
  [ 3] .strtab           STRTAB           0000000000000000  000010b8
       0000000000000022  0000000000000000           0     0     1
  [ 4] .shstrtab         STRTAB           0000000000000000  000010da
       0000000000000021  0000000000000000           0     0     1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  D (mbind), l (large), p (processor specific)

There are no section groups in this file.

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000000 0x0000000000400000 0x0000000000400000
                 0x000000000000100c 0x000000000000100c  R      0x1000

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

There is no dynamic section in this file.

There are no relocations in this file.
No processor specific unwind information to decode

Symbol table '.symtab' contains 7 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS test.asm
     2: 000000000040100c     0 NOTYPE  LOCAL  DEFAULT    1 _end
     3: 0000000000401000     0 NOTYPE  GLOBAL DEFAULT    1 _start
     4: 000000000040200c     0 NOTYPE  GLOBAL DEFAULT    1 __bss_start
     5: 000000000040200c     0 NOTYPE  GLOBAL DEFAULT    1 _edata
     6: 0000000000402010     0 NOTYPE  GLOBAL DEFAULT    1 _end

No version information found in this file.

• 使用objdump -D test.o反汇编目标文件，指令逻辑无异常，输出如下：

test.o:     file format elf64-x86-64


Disassembly of section .TEXT:

0000000000000000 <_start>:
   0:   b8 3c 00 00 00          mov    $0x3c,%eax
   5:   bf 00 00 00 00          mov    $0x0,%edi
   a:   0f 05                   syscall

根因分析 #

段错误由段名大小写不匹配导致：
汇编代码中定义的代码段名为大写.TEXT，但ld默认链接脚本仅识别小写.text为标准代码段，最终生成的可执行文件中，存放代码的LOAD段仅被标记为*可读（R）权限，未标记可执行（X）*权限。CPU跳转到入口地址尝试执行指令时，会因内存页无执行权限触发保护故障，直接抛出段错误。

解决方案 #

将汇编代码中的段名从大写.TEXT修改为小写.text即可，修正后代码如下：

SECTION .text
        GLOBAL _start

_start:
        mov rax, 60
        mov rdi, 0
        syscall

重新执行编译链接命令后，生成的可执行文件可正常运行，无段错误。

内容的提问来源于stack exchange，提问作者ElvisResurrected