Re: C++ related core dump

[Daniel Jacobowitz <drow at false dot org>]

On Tue, Nov 15, 2005 at 11:15:20AM +0100, Mark Kettenis wrote:
> I'm debugging some evil C++ code at work, and gdb keeps dumping core
> on me:
> 
> (gdb) ptype antennac 
> type = class ROScalarColumn<int> : public virtual ROTableColumn {

...

>     Int operator()(unsigned int) const;

> (gdb) p antennac(0)
> Segmentation fault (core dumped)
> 
> This is with gcc 3.2 on sparc-sun-solaris2.7, which still uses stabs
> debugging info.
> 
> I tracked it down to some code in valops.c:find_overload_match(),
> where SYMBOL_CPLUS_DEMANGLED_NAME is returning a null pointer which we
> pass to cp_func_name() and that function can't deal with that.  As a
> stopgap, I applied the attached patch, and now I get:
> 
> (gdb) p antennac(0)
> Invalid data type for function to be called.
> 
> which isn't quite what I want, but at least keeps my gdb alive.
> 
> What I really want of course is for the above to invoke
> antennac.operator()(0).  Is that supposed to work at all?  I know
> stabs support for C++ has issues, but reading the code I don't see how
> this would work for DWARF2 either.

Well certainly that's not going to work :-)  antennac(0) is not an
invocation of operator().  It's an invocation of the antennac class
constructor.  If you want to invoke operator(), you need an object.
If you had an object, I would expect this to work (or mostly work); GDB
does support user-defined operators.

GDB does _not_ support calling constructors, though.  This is a bit
tricky.

> Regardless of properly invoking operator(), we should do something
> about this crash.  Can we do something better than the attached patch?

> -      func_name	= cp_func_name (qualified_name);
> +      if (qualified_name)
> +	func_name = cp_func_name (qualified_name);

Return earlier if fsym is not a function?  Or this seems reasonable, to
avoid the crash.

-- 
Daniel Jacobowitz
CodeSourcery, LLC