So what is wrong with v3 C++

Daniel Berlin dan@cgsoftware.com
Sat Jun 30 12:30:00 GMT 2001


Jim Blandy <jimb@zwingli.cygnus.com> writes:

> Daniel Berlin <dan@cgsoftware.com> writes:
>> It's actually a bit worse than just needing to rewrite the dwarf2 reader.
>> 
>> You actually can't fix the stabs reader without gcc's help and a hack.
>> For the stabs reader, you need to hack gcc to output fully qualified names 
>> for us.
>> This is because if you look at the stabs section, you'll see we output 
>> types by the normal name, instead of mangled name (types have no mangled 
>> name, so it would be tricky to output them :P).
>> So we end up with numpunct<char> or, in this case "A".
>> 
>> For DWARF2, we now have namespace support, and i'll see if i can get it 
>> into 3.0.1.  So instead of just seeing:
>> 
>> DW_TAG_structure_type:
>> 	DW_AT_name: A
>> we now see
>> DW_TAG_namespace
>> 	DW_AT_name: N
>> 	DW_TAG_structure_type:
>> 		DW_AT_name: A
>> 
>> and pull "N::A" out of this.
>> Yay!
> 
> Can you post the GCC patches for generating namespace information
> here?  That way, we can start working on GDB's support, and be ready
> when GCC catches up.
Sure.
I'll just forward what i sent to gcc-patches.
I'll also post a new version of the new dwarf2 reader with namespace
support.


> 
> (It seems to me that, if GCC is processing code that uses namespaces,
> and generating mangled names and typeinfo objects that contain
> prefixed names, but emitting Dwarf 2 information that has no record of
> those prefixes, that should be called a GCC bug.  So it should be safe
> to count on it getting fixed, whether or not using your patch.)

Yes. The real problem we are running into, of course, is that types
themselves have no mangled names.
And if you fully qualified the name in the DW_AT_name attribute, you'd
run into all sorts of problems because DWARF2 really *can* support the
info we need, it just didn't output it. 
So it's an obviously broken thing, because we have 0 chance of getting
the info we need. it's simply not there.

> 
>> In both the stabs (for all cases), and dwarf2 (for 3.0 compiled files only, 
>> assuming it gets into 3.0.1), we could insert amazingly evil hacks to try 
>> to seperate out the namespace from the demangled names on other real 
>> members of the structure/type/whatever.
> 
> That does sound evil.
> 
> GDB has a tradition of accomodating broken debug info producers.  But
> even when we can pin the problem on a specific version of the
> compiler, those accomodations make the code harder to work with.  "If
> I make this change, will it break our GCC 3.0 support?  I don't have
> GCC 3.0 installed anywhere anymore..."
> 
> But until someone fixes stabs, I think it's reasonable to tell C++
> users that GCC only provides sufficient information when using Dwarf
> 2.

-- 
"I didn't get a toy train like the other kids.  I got a toy
subway instead.  You couldn't see anything, but every now and
then you'd hear this rumbling noise go by.
"-Steven Wright



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