Why does the following instruction not jump in gdb?

Question

I have the following program, exitc.s:

[OP@localhost linking]$ cat exitc.s
    .section .text
    .globl _start

_start:
    call exit

Built in the following way:

[OP@localhost linking]$ as exitc.s -o exitc.o
[OP@localhost linking]$ ld exitc.o -o exitc -lc -I /usr/lib64/ld-linux-x86-64.so.2 

When running it through gdb , the following occurs:

(gdb) disas _start
Dump of assembler code for function _start:
   0x0000000000401020 <+0>: callq  0x401010 <exit@plt>
End of assembler dump.
(gdb) break *_start
Breakpoint 1 at 0x401020
(gdb) run
Starting program: /path/to/linking/exitc 

Breakpoint 1, 0x0000000000401020 in _start ()
(gdb) disas _start
Dump of assembler code for function _start:
=> 0x0000000000401020 <+0>: callq  0x401010 <exit@plt>
End of assembler dump.
(gdb) si
0x0000000000401010 in exit@plt ()
(gdb) disas 0x401010
Dump of assembler code for function exit@plt:
=> 0x0000000000401010 <+0>: jmpq   *0x2002(%rip)        # 0x403018 <exit@got.plt>
   0x0000000000401016 <+6>: pushq  $0x0
   0x000000000040101b <+11>:    jmpq   0x401000
End of assembler dump.
(gdb) si
0x0000000000401016 in exit@plt ()
(gdb) disas 0x401010
Dump of assembler code for function exit@plt:
   0x0000000000401010 <+0>: jmpq   *0x2002(%rip)        # 0x403018 <exit@got.plt>
=> 0x0000000000401016 <+6>: pushq  $0x0
   0x000000000040101b <+11>:    jmpq   0x401000
End of assembler dump.

In the last step of the assembly, why does a jump not occur?

Answer 1

In the last step of the assembly, why does a jump not occur?

The JUMP does occur, but just happens to jump to the next instruction.

That is entirely expected, and is how lazy symbol resolution works. You can read about it eg here .