Move execution point in Xcode/lldb - ios

Question

Is there a way to set the execution point while debugging Xcode/lldb? To be more specific, after hitting a breakpoint, moving the execution point manually to another line of code?

Answer 1

If you're looking at moving it up or down with in a method you can click and drag the green arrow to a specific point. so if you want to back up a line before the breakpoint. click on the green arrow that is produced and drag it up. If you hit run you'll hit your breakpoint again

Answer 2

In Xcode 6, you can use j lineNumber - see documentation below:
(lldb) help j
Sets the program counter to a new address. This command takes 'raw' input
(no need to quote stuff).
Syntax: _regexp-jump [<line>]
_regexp-jump [<+-lineoffset>]
_regexp-jump [<file>:<line>]
_regexp-jump [*<addr>]
'j' is an abbreviation for '_regexp-jump'

Answer 3

One of the great things about lldb is that it's easy to extend it with a little bit of python scripting. For instance, I threw together a new jump command without much trouble:
import lldb
def jump(debugger, command, result, dict):
"""Usage: jump LINE-NUMBER
Jump to a specific source line of the current frame.
Finds the first code address for a given source line, sets the pc to that value.
Jumping across any allocation/deallocation boundaries (may not be obvious with ARC!), or with optimized code, quickly leads to undefined/crashy behavior. """
if lldb.frame and len(command) >= 1:
line_num = int(command)
context = lldb.frame.GetSymbolContext (lldb.eSymbolContextEverything)
if context and context.GetCompileUnit():
compile_unit = context.GetCompileUnit()
line_index = compile_unit.FindLineEntryIndex (0, line_num, compile_unit.GetFileSpec(), False)
target_line = compile_unit.GetLineEntryAtIndex (line_index)
if target_line and target_line.GetStartAddress().IsValid():
addr = target_line.GetStartAddress().GetLoadAddress (lldb.target)
if addr != lldb.LLDB_INVALID_ADDRESS:
if lldb.frame.SetPC (addr):
print "PC has been set to 0x%x for %s:%d" % (addr, target_line.GetFileSpec().GetFilename(), target_line.GetLine())
def __lldb_init_module (debugger, dict):
debugger.HandleCommand('command script add -f %s.jump jump' % __name__)
I put this in a directory where I keep Python commands for lldb, ~/lldb/, and I load it in my ~/.lldbinit file with
command script import ~/lldb/jump.py
and now I have a command jump (j works) which will jump to a given line number. e.g.
(lldb) j 5
PC has been set to 0x100000f0f for a.c:5
(lldb)
This new jump command will be available both in command-line lldb and in Xcode if you load it in your ~/.lldbinit file -- you'll need to use the debugger console pane in Xcode to move the pc instead of moving the indicator in the editor window.

Answer 4

You can move the program counter (pc) in lldb using the lldb command register write pc. But it's instruction based.
There's an excellent lldb/gdb comparison here that is useful as an lldb overview.