《coredump问题原理探究》Linux x86版5.9节C风格数据结构内存布局之联合体

1	 #include <stdio.h>
  2	 union xuzhina_dump_c05_s4
  3	 {
  4	     int i;
  5	     char hello[4];
  6	 };
  7 
  8	 int main()
  9	 {
 10	     union xuzhina_dump_c05_s4 test;
 11	     test.i = 0x656463;
 12	     for ( int i = 0; i < 4; i++ )
 13	     {
 14	         printf( "%c", test.hello[i] );
 15	     }
 16	 
 17	     printf( "\n" );
 18	     return 0;
 19	 }

(gdb) disassemble main
Dump of assembler code for function main:
   0x08048570 <+0>:     push   %ebp
   0x08048571 <+1>:     mov    %esp,%ebp
   0x08048573 <+3>:     and    $0xfffffff0,%esp
   0x08048576 <+6>:     sub    $0x20,%esp
   0x08048579 <+9>:     movl   $0x656463,0x18(%esp)
   0x08048581 <+17>:    movl   $0x0,0x1c(%esp)
   0x08048589 <+25>:    jmp    0x80485a8 <main+56>
   0x0804858b <+27>:    lea    0x18(%esp),%edx
   0x0804858f <+31>:    mov    0x1c(%esp),%eax
   0x08048593 <+35>:    add    %edx,%eax
   0x08048595 <+37>:    movzbl (%eax),%eax
   0x08048598 <+40>:    movsbl %al,%eax
   0x0804859b <+43>:    mov    %eax,(%esp)
   0x0804859e <+46>:    call   0x8048430 <putchar@plt>
   0x080485a3 <+51>:    addl   $0x1,0x1c(%esp)
   0x080485a8 <+56>:    cmpl   $0x3,0x1c(%esp)
   0x080485ad <+61>:    setle  %al
   0x080485b0 <+64>:    test   %al,%al
   0x080485b2 <+66>:    jne    0x804858b <main+27>
   0x080485b4 <+68>:    movl   $0xa,(%esp)
   0x080485bb <+75>:    call   0x8048430 <putchar@plt>
   0x080485c0 <+80>:    mov    $0x0,%eax
   0x080485c5 <+85>:    jmp    0x80485cf <main+95>
   0x080485c7 <+87>:    mov    %eax,(%esp)
   0x080485ca <+90>:    call   0x8048460 <_Unwind_Resume@plt>
   0x080485cf <+95>:    leave  
   0x080485d0 <+96>:    ret    
End of assembler dump.

   0x08048579 <+9>:     movl   $0x656463,0x18(%esp)

   0x0804858b <+27>:    lea    0x18(%esp),%edx
   0x0804858f <+31>:    mov    0x1c(%esp),%eax
   0x08048593 <+35>:    add    %edx,%eax
   0x08048595 <+37>:    movzbl (%eax),%eax