How to step-into, step-over and step-out with GDB?

Question

I typed help while I was in the GDB but didn't find anything about step-into, step-over and step-out. I put a breakpoint in an Assembly program in _start (break _start). Afterwards I typed next and it finished the debugging. I guess it was because it finished _start and didn't step-into as I wanted.

Read the full GDB docs. As I recall, they were quite helpful about this, when I was first learning it. Unfortunately, I haven't needed to debug any program at that level for several decades, so the actual commands seem to have gotten swapped out in my brain. So, I can't really write an answer. But, if you do figure it out from the manuals, then you can answer your own question for a bonus. — MAP, Jul 24 '16 at 17:32
@MAP I'll try again. I tried to use a better debugger (KDbg) but I don't succeed to use it in Ubuntu. — Pichi Wuana, Jul 24 '16 at 17:38
gdb is a good debugger. You may want to use Emacs as its frontend. — Thorbjørn Ravn Andersen, Jan 02 '20 at 06:50

score 103 · Accepted Answer · answered Jul 24 '16 at 18:01

103

help running provides some hints:

There are step and next instuctions (and also nexti and stepi).

(gdb) help next
Step program, proceeding through subroutine calls.
Usage: next [N]
Unlike "step", if the current source line calls a subroutine,
this command does not enter the subroutine, but instead steps over
the call, in effect treating it as a single source line.

So we can see that step steps into subroutines, but next will step over subroutines.

The step and stepi (and the next and nexti) are distinguishing by "line" or "instruction" increments.

step -- Step program until it reaches a different source line
stepi -- Step one instruction exactly

Related is finish:

(gdb) help finish
Execute until selected stack frame returns.
Usage: finish
Upon return, the value returned is printed and put in the value history.

A lot more useful information is at https://sourceware.org/gdb/onlinedocs/gdb/Continuing-and-Stepping.html

answered Jul 24 '16 at 18:01

Stephen Harris

44,540

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What does it mean by until it reaches a different source line? – Pichi Wuana Jul 24 '16 at 18:04
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for(i=0;i<10;i++) { printf("%d\n",i); } is one source line but multiple instructions. – Stephen Harris Jul 24 '16 at 18:06
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Is there a way to step-out? I couldn't find it in help running. – nukeguy Aug 23 '17 at 16:34
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What do you mean by "step-out"? The finish command will complete the current stack frame, which will normally complete the current subroutine and return to the caller. – Stephen Harris Aug 24 '17 at 02:03
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@PichiWuana gdb will step through as many assembly instructions as necessary until the first instruction representing the next line of source code is reached – U007D Jul 26 '18 at 00:53
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finish or fin in GDB, is the step-out in IDEA or Eclipse. – Eric Feb 23 '20 at 08:18

score 8 · Answer 2 · answered Jan 01 '20 at 22:20

8

Use command 'finish'; this sometimes does the same thing as 'step-out'. It'll finish what the stack is doing (a function, usually), and go to the next line after that. Look up the command for more info.

answered Jan 01 '20 at 22:20

Nunuv Yurbizness

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score 3 · Answer 3 · answered Aug 16 '19 at 17:48

3

I came here because I had the same question. I eventually figured that for my purpose any time I could use something like "step-out" of a loop I can just set another breakpoint after the loop and then let the program continue to finish the loop and run into the breakpoint afterward. Sorry if that is obvious to most people but it is probably helpful for someone looking for an answer to this question.

answered Aug 16 '19 at 17:48

fjahr

131
2

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"Step out" in most other debuggers is "finish" in gdb. Not really to do with exiting a loop. – RichieHH Mar 02 '21 at 19:00
I think that's the until command that you ought to use for that. – Johan Boulé Apr 03 '23 at 11:50

How to step-into, step-over and step-out with GDB?

3 Answers3