Re: Next over function and breakpoint setting

[Daniel Jacobowitz <drow@false.org>]

On Tue, Mar 16, 2004 at 04:42:30PM +0100, Orjan Friberg wrote:
> Out of curiosity I followed what happens when issuing a next command 
> over a function call.  The reason I got curious was that I noticed 
> (remote protocol) that GDB sets a breakpoint on the first instruction of 
> the function being stepped over, and, when stopped there, sets another 
> breakpoint at that function's return address to accomplish the "next".
> 
> Actually, maybe that's a misrepresentation: looking at the code, it 
> seems GDB does a step, and if it *then* finds it ended up inside a 
> function (step_into_function -> step_over_function) it decides to step 
> out of it.
> 
> Looking at the code in infcmd.c and infrun.c I'm sure there's a good 
> reason for not just setting the breakpoint on the address belonging to 
> the next line of code, but I couldn't find any comment saying what that 
> reason is.  Anyone care to enlighten me?
> 
> (I couldn't say if any of this was remote target/CRIS specific; 
> apologies if it is and I missed it.)

[Sorry, missed this the first time.]

"The next line of code" is a very iffy concept.  GDB doesn't analyze a
line to figure out what it does, or where it might transfer control
to... while possible, that would be a very different approach to
debugging.  So the only way we have to implement next is to step and
see where we end up - and if we don't like it, go until we're somewhere
else.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer