Re: [RFC] breakpoints and function prologues...

[Daniel Jacobowitz <drow at mvista dot com>]

On Thu, Aug 15, 2002 at 01:57:13AM -0400, Andrew Cagney wrote:
> >I agree with Jim here.  I think most folks are actually surprised to find 
> >that if they break on the "{" beginning a function (or indeed anywhere 
> >before the first executable line of code) then their backtrace will not be 
> >correct.  Understanding why this is so requires you to "pay attention to 
> >the man behind the curtain", and that we breaks the illusion that source 
> >code maps straight-forwardly onto the running program.  Where this extra 
> >knowledge is helpful (like when debugging optimized code) it is fine to 
> >require folks to have it.  But here, where it really doesn't do any good, 
> >I think it is just confusing.  And, of course, it causes big heartburn for 
> >GUIs the varobj code, as I said earlier.
> >
> >I doubt that "{" breaks on the prologue is a crucial feature of gdb, and 
> >given that there are other ways to do this, I don't think it is really 
> >worth supporting...
> 
> Michael is right here.  If a CLI user sets a breakpoint on a line (with 
> code) then that user clearly wants the breakpoint set on that line.

Sure, if the user knows there's code there.  I don't think most of our
users would understand that there is code on the "{", or what it is
for - and I don't think that breaking by line number should break on
code inserted by the compiler rather than the user.

So I have to agree with Jim (both Jims, I think?).

> If an architecture can't unwind the frame for that breakpoint address 
> then that is a bug in the architecture and/or GDB.  The main reason the 
> average prologue analyzer doesn't handle breakpoints in the prologue is, 
> I think, more a factor of not being tested then of being ``hard''.

Most of our ports don't support it, however.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer