[問題] gdb 下斷點

[zha0 (這個帳號是掛網用)]

; hello.asm
; nasm -f elf -o hello.o hello.asm
; ld -o hello hello.o

section .text
        global _start

_start:
        mov edx, len
        mov ecx, msg
        mov ebx, 1
        mov eax, 4
        int 0x80

        mov eax, 1
        int 0x80

section .data

msg     db      'Hello world!', 0xa
len     equ     $-msg

----------------------------------------------
[root@localhost ~]# readelf -h hello
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Intel 80386
  Version:                           0x1
  Entry point address:               0x8048080
........
----------------------------------------------
[root@localhost ~]# gdb hello
...

(gdb) disas 0x8048080
Dump of assembler code for function _start:
0x08048080 <_start+0>:  mov    $0xd,%edx
0x08048085 <_start+5>:  mov    $0x80490a0,%ecx
0x0804808a <_start+10>: mov    $0x1,%ebx
0x0804808f <_start+15>: mov    $0x4,%eax
0x08048094 <_start+20>: int    $0x80
0x08048096 <_start+22>: mov    $0x1,%eax
0x0804809b <_start+27>: int    $0x80
End of assembler dump.
(gdb) b *0x8048080
Breakpoint 1 at 0x8048080
(gdb) r
Starting program: /root/hello
(no debugging symbols found)
Hello world!

Program exited with code 01.
(gdb)

為什麼在 0x8048080 下了斷點，但使用 r 執行都不會停在該斷點上呢 ?

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→ zha0:一定要插 0xcc 在開頭嗎 ?___?
推 lungswu:b *0x8048085   這樣可以接受嗎？
→ zha0:因為對齊的關係嗎 ?
→ zha0:i r
→ zha0:eip            0x8048085
→ zha0:但用 (gdb) disas $eip 出來是從 80 開始 .
→ zha0:Dump of assembler code for function _start:
→ zha0:0x08048085 <_start+5>:  mov    $0x80490a0,%ecx
→ zha0:0x0804808a <_start+10>: mov    $0x1,%ebx
→ zha0:0x08048080 <_start+0>:  mov    $0xd,%edx
推 lungswu:這單純為了解決不能在想要的地方中斷，在下一個指令下中斷
→ lungswu:於*0x8048085中斷，是*0x08048080已經執行，暫存器也已經
→ lungswu:更新，接著要執行0x08048085前
→ lungswu:至於為什麼不能被停止在*0x8048080，是個值得研究的課題