[Lazarus] Conditional Debugger breakpoints not working ?

Michael Van Canneyt michael at freepascal.org
Mon Feb 20 15:14:01 CET 2023

On Mon, 20 Feb 2023, Martin Frb via lazarus wrote:

> On 20/02/2023 13:46, Michael Van Canneyt via lazarus wrote:
>> I suggest you adapt the wiki to clarify all this.
>> While you're at it, The link in the wiki page to the gdb convenience
>> functions is broken.
> updated
>> In general, I don't think you can expect the user to know that he should 
>> use $_streq(myvar, "hello"), specially the cmem condition that seems 
>> necessary.
>> Ideally, the IDE could detect a string and transform the expression.
> This always has been the issue with gdb.
> If you had a watch with anything but just a plain variable name, then gdb may 
> give you:
> - an error,
> - or an incorrect result,
> - or the correct result
> For watches, there is quite a lot of code in the IDE to try and fix those 
> things.
> There are testcases, that can be run with different debug-info, and diff gdb 
> versions. (And they run for many hours / and unfortunately still have some 
> errors, some false errors...).
> But there is no way to get to 100%. In many cases gdb simple does not give 
> enough info to detect the necessary information on the underlaying type. (And 
> when trying to get this, one has to be carefully not to crash gdb).
> Also it makes evaluating each individual watch a lot slower (at least factor 
> 3 or 4). Though on that I have always pushed the point that a "correct 
> result" is worth *any* wait time.

Yes. An incorrect result may result in infinite wait time :-)

> In any case, with conditional breakpoints it would be even more complex....
> It would be nice to have, but with the availability of FpDebug, it is very 
> unlikely that will be fixed. (There are simply a lot of other things that 
> (should) have more priority)
> I may add a warning to the breakpoint dlg, that for non-fpdebug will display 
> a red TLabel below the input, with some text that the condition may not work 
> at all.

I think this is a good idea.

> It is a problem on Mac, with LLDB. Though I am not even sure that conditional 
> breakpoint are supported at all...

They are:

> LLDB probably can do them (with restrictions like gdb). But the IDE has 
> absolutely on code to translate "pascal to lldb" => because for watches it 
> can evaluate with fpdebug.
> But conditional breakpoints must be done by lldb, or they become very very 
> slow. (That is if they need to pass lots of time before they match the 
> condition, and each hit pass 1 second or more, you quickly get to several 
> minutes of wait time)

No problem. I realize it is not easy to solve generally, although a 
solution for 'simple' strings would be welcome.

I'll stick to poor man's conditionals. 
Then the compiler will tell me what I do wrong :)


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