在程序入口处打断点

方法一：

$ strip a.out
$ readelf -h a.out 
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:               0x400440
  Start of program headers:          64 (bytes into file)
  Start of section headers:          4496 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         9
  Size of section headers:           64 (bytes)
  Number of section headers:         29
  Section header string table index: 28

方法二：

$ gdb a.out 
>>> info files
Symbols from "/home/me/a.out".
Local exec file:
    `/home/me/a.out', file type elf64-x86-64.
    Entry point: 0x400440
    0x0000000000400238 - 0x0000000000400254 is .interp
    0x0000000000400254 - 0x0000000000400274 is .note.ABI-tag
    0x0000000000400274 - 0x0000000000400298 is .note.gnu.build-id
    0x0000000000400298 - 0x00000000004002b4 is .gnu.hash
    0x00000000004002b8 - 0x0000000000400318 is .dynsym
    0x0000000000400318 - 0x0000000000400355 is .dynstr
    0x0000000000400356 - 0x000000000040035e is .gnu.version
    0x0000000000400360 - 0x0000000000400380 is .gnu.version_r
    0x0000000000400380 - 0x0000000000400398 is .rela.dyn
    0x0000000000400398 - 0x00000000004003e0 is .rela.plt
    0x00000000004003e0 - 0x00000000004003fa is .init
    0x0000000000400400 - 0x0000000000400440 is .plt
    0x0000000000400440 - 0x00000000004005c2 is .text
    0x00000000004005c4 - 0x00000000004005cd is .fini
    0x00000000004005d0 - 0x00000000004005e0 is .rodata
    0x00000000004005e0 - 0x0000000000400614 is .eh_frame_hdr
    0x0000000000400618 - 0x000000000040070c is .eh_frame
    0x0000000000600e10 - 0x0000000000600e18 is .init_array
    0x0000000000600e18 - 0x0000000000600e20 is .fini_array
    0x0000000000600e20 - 0x0000000000600e28 is .jcr
    0x0000000000600e28 - 0x0000000000600ff8 is .dynamic
    0x0000000000600ff8 - 0x0000000000601000 is .got
    0x0000000000601000 - 0x0000000000601030 is .got.plt
    0x0000000000601030 - 0x0000000000601040 is .data
    0x0000000000601040 - 0x0000000000601048 is .bss

技巧

当调试没有调试信息的程序时，直接运行start命令是没有效果的：

(gdb) start
Function "main" not defined.

如果不知道main在何处，那么可以在程序入口处打断点。先通过readelf或者进入gdb，执行info files获得入口地址，然后：

(gdb) b *0x400440
(gdb) r