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Re: question for gdb users...
Re: question for gdb users...
Thu, 24 Sep 2009 00:50:47 -0700
On Thu, Sep 24, 2009 at 12:16 AM, Richard Frith-Macdonald
> On 24 Sep 2009, at 04:40, Matt Rice wrote:
>> there is some discussion here about removing the convenience mechanism
>> that allows
>> you to go
>> break foo
>> where foo then turns into -[class foo]
>> this causes lots of issues which are fairly hard to fix in gdb,
>> which is why the whole 'break main' with recent gdb causes issues. because
>> [NSThread main].
>> if you guys opposed to it please let me know and I will relay it into
>> the gdb thread,
>> I for one wasn't even aware of this feature until it started causing
>> here is the thread.
> I use this feature tens of times a day, perhaps more ... it's actually
> almost the only way I set breakpoints (though I occasionally set breakpoints
> at particular lines or in C functions).
> Now, it's not obvious, from a quick read of the thread, why there is a
> specific problem with objc ... though it seems to imply that objc is a
> special case and this feature is fine in C++ and desired in pascal and ada.
The specific problem is that gdb resets breakpoints upon shared
library load, in case symbols were overriden by c-linkage behaviour
the 'canonical' version of 'main' is 'main', where the canonical
version of '-[NSThread main]'
when gdb resets the breakpoint on shared library load to check for a
new address for 'main'. it will respond with more than one address,
because main is ambiguous, so its unable to tell which of the symbols
you actually want a breakpoint on.
now imagine if the function was named init :)
c++ doesn't suffer from this problem,
because they don't do this,
will set a breakpoint on a function bar regardless of the existance of
a method Foo::bar(void)
most languages won't have this issue simply because they don't have
their function calling/method dispatch syntax split, calling a foo
function or method uses the same syntax. ObjC is different.
> I don't mind using the 'break [class method]' syntax where I know that the
> implementation of the method is in one particular class, but *usually* I
> don't know which class I want to break in (because I'm not aware of all the
> libraries/subclasses that might be involved).
> If the underlying problem is one of confusion between objc methods and C
> functions (the example of the confusion between the main() function and the
> [NSThread-main] method suggests that this may be the case) then perhaps it
> could be resolved using a modification of the square brackets syntax ...
> at present we have:
this is also a problem with category methods now, i'll work on fixing
it but its not going to make the release, until then you can specify
the category explicitly. by break -[Foo(bar) method]
because -[Foo method] may expand to both -[Foo(bar) method] and -[Foo
method]... this is only the case for overridden methods with
breakpoints on them though.
> +[class method] a factory method of a specific class
> -[class method] in instance method in a particular class
> [class method] either a factory method or an instance method, with an
> option to choose if both exist
> and could add:
> +[method] a factory method of any class
> -[method] in instance method in any class
> [method] either a factory method or an instance method,
these are good ideas, I was thinking
+method/-method and was kind of perplexed on what to do for both,
[method] might work, i was also thinking ?method, which has no real
objc relation, but might be familiar to those using the shell?
> So 'break [method] would be like the current 'break method' syntax but
> 'method' would be treated *only* as an ObjC method name, never as a function
> or method in another language.
> If this would help resolve the issue, it would satisfy me. Simply losing
> the ability to set a breakpoint in any class would not.
you could still do this with the rbreak command,
by using 'rbreak .*methodname.*
so even if we remove the function and we don't reintroduce an
alternative syntax this is still possible.