Re: debugging a callq command

Excuse me, I missed something while pasting the output. The correct output is:

(gdb) nexti
0x00007fffffffde6e in ?? ()
1: x/20i $pc
=> 0x7fffffffde6e:    jmp    0x7fffffffde7d
   0x7fffffffde70:    pop    %rsi
   0x7fffffffde71:    xor    %ecx,%ecx
   0x7fffffffde73:    mov    $0x21,%cl
   0x7fffffffde75:    xorb   $0x35,(%rsi)
   0x7fffffffde78:    rex.RX loop 0x7fffffffde75
   0x7fffffffde7b:    jmp    0x7fffffffde82
   0x7fffffffde7d:    callq  0x7fffffffde70
   0x7fffffffde82:    pop    %rdi
   0x7fffffffde83:    jae    0x7fffffffdef2
   0x7fffffffde85:    add    $0xee,%al
   0x7fffffffde87:    add    $0xfc,%al
   0x7fffffffde89:    clc    
   0x7fffffffde8a:    mov    $0x4,%ch
   0x7fffffffde8c:    out    %eax,$0x5f
   0x7fffffffde8e:    ds insl (%dx),%es:(%rdi)
   0x7fffffffde90:    addr32 pop %rbp
   0x7fffffffde92:    sbb    0x46(%rdi),%cl
   0x7fffffffde95:    pop    %rbp
   0x7fffffffde96:    pop    %rbp
(gdb) nexti
0x00007fffffffde7d in ?? ()
1: x/20i $pc
=> 0x7fffffffde7d:    callq  0x7fffffffde70
   0x7fffffffde82:    pop    %rdi
   0x7fffffffde83:    jae    0x7fffffffdef2
   0x7fffffffde85:    add    $0xee,%al
   0x7fffffffde87:    add    $0xfc,%al
   0x7fffffffde89:    clc    
   0x7fffffffde8a:    mov    $0x4,%ch
   0x7fffffffde8c:    out    %eax,$0x5f
   0x7fffffffde8e:    ds insl (%dx),%es:(%rdi)
   0x7fffffffde90:    addr32 pop %rbp
   0x7fffffffde92:    sbb    0x46(%rdi),%cl
   0x7fffffffde95:    pop    %rbp
   0x7fffffffde96:    pop    %rbp
   0x7fffffffde97:    sbb    0x5c(%rdi),%dl
   0x7fffffffde9a:    pop    %rbx
   0x7fffffffde9b:    mov    $0xbc6667d6,%esp
   0x7fffffffdea0:    (bad)  
   0x7fffffffdea1:    clc    
   0x7fffffffdea2:    mov    $0x90,%ch
   0x7fffffffdea4:    nop
(gdb) nexti

Program received signal SIGSEGV, Segmentation fault.
0x00007fffffffde8c in ?? ()
1: x/20i $pc
=> 0x7fffffffde8c:    out    %eax,$0x5f
   0x7fffffffde8e:    ds insl (%dx),%es:(%rdi)
   0x7fffffffde90:    addr32 pop %rbp
   0x7fffffffde92:    sbb    0x46(%rdi),%cl
   0x7fffffffde95:    pop    %rbp
   0x7fffffffde96:    pop    %rbp
   0x7fffffffde97:    sbb    0x5c(%rdi),%dl
   0x7fffffffde9a:    pop    %rbx
   0x7fffffffde9b:    mov    $0xbc6667d6,%esp
   0x7fffffffdea0:    (bad)  
   0x7fffffffdea1:    clc    
   0x7fffffffdea2:    mov    $0x90,%ch
   0x7fffffffdea4:    nop
   0x7fffffffdea5:    nop
   0x7fffffffdea6:    nop
   0x7fffffffdea7:    nop
   0x7fffffffdea8:    nop
   0x7fffffffdea9:    nop
   0x7fffffffdeaa:    nop
   0x7fffffffdeab:    nop



Regards,
Mahmood 

    On Friday, July 6, 2018, 3:45:53 PM GMT+4:30, Mahmood Naderan via gdb <[email protected]> wrote:  
 
 Hi,
Trying to debug an assembly code with gdb, I see that a call function to a valid address exists but the control won't go to the target address.

As you can see, the first instruction is a jmp to 0x7fffffffde7d and there, it will call 0x7fffffffde70. However, the next instruction is something else while the program receives seg fault.