[PATCH] Remove wild .debug_aranges entries generated from unimportant labels

Richard Mitton richard at codersnotes.com
Wed Oct 2 16:21:06 PDT 2013

I'd rather keep it in. I'm sure gcc might not emit the arange table 
correctly, but the DWARF specs are quite clear that the idea of an 
arange table is to map *every* byte in the program to it's debug CU. Not 
just text. If there's a reference in the debug_info to an address, the 
arange table should have the reverse of that. This is why I used the 
label list to generate it, rather than trying to pick out 
functions/variables/etc. The labels added to debug_info define exactly 
the set of addresses required.

Common symbols have an address in the final program, so they should be 
included too.

Debuggers historically don't always use the full capabilities of the 
DWARF data, because the compilers don't generate correct data. If we fix 
the compiler here once and for all, it enables future debuggers to make 
use of it.

The biggest challenge faced by debuggers today is compilers which only 
emit barely enough DWARF to function. We can do better than that.

> Eric Christopher <mailto:echristo at gmail.com>
> Wednesday, October 02, 2013 2:35 PM
> *nod* The fix is fine.
> I think the additional complication that got us here is the adding of
> data symbols to aranges. Now, as far as I can tell, gcc doesn't emit
> aranges for any of them, however, the real problem for us are common
> symbols. I think we want to omit ranges for common symbols - it
> doesn't really seem to make sense anyhow.
> I know that gdb and the various gnu tools don't use that part of the
> information, but I don't know of any other users. So objections to
> removing that part? It'll definitely greatly simplify the code.
> -eric
> Richard Mitton <mailto:richard at codersnotes.com>
> Wednesday, October 02, 2013 2:00 PM
> LGTM, although I dunno if I'm actually authorized to approve patches :)
> There's code in there already that ignores labels in metadata 
> sections, but it wasn't getting triggered because debug_loc labels are 
> added after the test for it. And the stupid sectionless common symbols 
> mean that it couldn't just ignore NULL sections either.
> This looks like a fine fix.
> Richard Mitton
> richard at codersnotes.com
> On 10/02/2013 01:33 PM, Alexey Samsonov wrote:
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> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
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