Can I use gdb to skip a line without having to type line numbers?

Question

I know I can use jump to set the program counter to a specific line and so I can skip one or more lines (or execute some lines again). Can I easily just skip the next line without having to enter line numbers?

This would be very convenient to "comment out" something at run time.

Related: more general stuff about using `jump` (e.g. that it's only safe inside the current function, and only if you compiled with `-O0`): https://stackoverflow.com/questions/4116632/is-it-possible-to-jump-skip-in-gdb-debugger/46043760#46043760 — Peter Cordes, Sep 04 '17 at 20:38

score 88 · Accepted Answer · edited Dec 05 '13 at 10:05

88

jump +1

jumps to the next line line i.e. skipping the current line. You may also want to combine it with tbreak +1 to set a temporary breakpoint at the jump target.

See http://sourceware.org/gdb/current/onlinedocs/gdb/Specify-Location.html for more ways of expressing locations with gdb.

Note that without a breakpoint gdb is likely to continue execution normally instead of jumping. So if jumping doesn't seem to work, make sure you set a breakpoint at the destination.

edited Dec 05 '13 at 10:05

Craig Ringer

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answered Oct 27 '10 at 20:32

laalto

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Pretty obvious, but thanks! Works great in Xcode using breakpoints with Debugger Command. – Ortwin Gentz Oct 27 '10 at 20:52
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It should be noted that this works in LLDB as well. :) – Ortwin Gentz Dec 15 '14 at 17:28
If you're working directly in asm, you can jump to the instruction that you want by issuing a `j addr` where `addr` is the address where you want to jump to. – dionyziz Mar 03 '17 at 14:41
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Note that this is only going to work as a source-level skip if you compiled with `-O0`. Any optimization will make it unsafe to skip around. – Peter Cordes Sep 04 '17 at 20:29

score 28 · Answer 2 · answered Apr 08 '16 at 17:29

28

I have the following in my .gdbinit config file:

define skip
    tbreak +1
    jump +1
end

So just type skip in gdb to skip a line.

answered Apr 08 '16 at 17:29

gospes

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How to parametrize it to "skip(N)" ? – p2rkw Sep 13 '16 at 17:32
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@p2rkw. You can replace '1' with $arg0, as explained here: https://sourceware.org/gdb/onlinedocs/gdb/Define.html. Be aware that I would not use the name 'skip' anymore, because it became a GDB function (allowing to skip source files while stepping through your code). – gospes Mar 12 '17 at 09:03
@Trass3r True. I mention this in the comment above. – gospes Sep 15 '20 at 07:50

score 5 · Answer 3 · answered Aug 16 '13 at 03:14

5

To Skip Any Numbers of Lines during Execution:

[Current Position -- in GDB] Line N
.......... // Lines To Skip
..........
..........
[Line To Execute - After Jumping] Line M

Put a Breakpoint on Line M:

gdb$b M

Jump To Line M:

gdb$jump M

answered Aug 16 '13 at 03:14

Sandeep Singh

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Can I use gdb to skip a line without having to type line numbers?

3 Answers3

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