Re: [rfc breakpoint] Catch exceptions

Jim Ingham
2003-03-26T02:14:27Z

On Tuesday, March 25, 2003, at 04:03 PM, Daniel Jacobowitz wrote:

> On Tue, Mar 25, 2003 at 03:51:32PM -0800, Jim Ingham wrote:
>> One thing we had to worry about at least on Mac OS X is that we don't
>> use a shared libstdc++, rather every shlib that uses C++ get its own
>> copy of all the libsupc++ code. So there are actually many copies of
>> __cxa__begin_catch hanging around. To do this properly, you have to
>> search exhaustively for these symbols, not just take the first hit.
>> Moreover, you have to redo it on every shared library load, or you
>> will
>> miss some. This still might bite you on other systems, for instance
>> if
>> out of paranoia somebody had linked their shlib or executable
>> statically to libstdc++.a (so they wouldn't get bit by changing ABI
>> issues or whatever).
>>
>> BTW. The more general problem of a symbol resolving to multiple
>> instances - for instance setting file:line breakpoints in inlined
>> functions or template method defn's - is something we need to address.
>> It really ticks off our C++ friends. I thought I was going to have
>> time to think about this in the next month or two, but I got
>> sidetracked on other issues. But I will need to get back to it after
>> our WWDC (in June).
>
> Yes. Rather than focusing on it with a special hack here, I'd rather
> eventually address it properly. Thanks for pointing this out.

That seems fine.

>
>> I thought from some comments in other notes that this was something
>> you
>> were thinking about as well, Daniel. Is that true?
>
> I'm interested in the problem, but like everyone I have a dreadful
> shortage of time :(
>

Another complication we should address is that gdb currently tries to
reset all breakpoints in all shared libraries when it does
breakpoint_re_set_all... It would be better if gdb could figure out
which shared libraries have been added on a shlib event, and only reset
in them. This seems trivial, but on Mac OS X (and I bet on a fully
loaded KDE or Gnome system) there are LOTS of shared libraries, and
this is a major speed problem. It is even worse for systems with
shared library based plugins, where you can end up loading ~100 plugins
one by one. Setting ~20 or 30 breakpoints for all the shlibs in the
system plus the increasing list from the plugins, for each load of 100
plugins, really dogs down...

I think I know how to do this on our gdb, but it will take some more
thought to figure out how to do it generically...

Jim
--
Jim Ingham jingham@apple.com
Developer Tools
Apple Computer