r274246 - [codeview] Emit qualified display names if -gline-tables-only is on

[Nico Weber via cfe-commits]

On Fri, Jul 8, 2016 at 3:57 PM, David Blaikie via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

>
>
> On Thu, Jul 7, 2016 at 4:10 PM, Reid Kleckner <rnk at google.com> wrote:
>
>> On Thu, Jul 7, 2016 at 3:45 PM, David Blaikie <dblaikie at gmail.com> wrote:
>>
>>> Yeah - is this necessary for CodeView? (does something break, or do you
>>> just get simple names where you'd prefer full mangled or qualified names)
>>>
>>> It was chosen pretty deliberately to do it this way (use unqualified
>>> names) for gmlt to keep size down. Have you got numbers for the size delta
>>> for CodeView with this change? I'd really prefer to make the same choice
>>> for both - it'd seem a bit arbitrary to choose our size optimization based
>>> on differences in the kind of workloads we happen to have on these two
>>> platforms.
>>>
>>
>> It's problematic for CodeView because there is no equivalent field like
>> DW_AT_linkage_name in any of the symbol records. There is only the display
>> name, which includes scope qualifiers.
>>
>> I'm suggesting we reverse our decision for DWARF because our space saving
>> optimization breaks standard stack dumpers on Linux (gdb and addr2line),
>>
>
> What breakage are you referring to here?
>
> If we're talking about printing out the simple name - that comes up even
> in llvm-symbolizer if a function is inlined. So I think that's an
> intentional tradeoff that would apply to CV as well.
>
>
>> and that seems like a Bad Thing. Instead we've told users to user
>> llvm-symbolizer, which is OK, but kind of crappy.
>>
>
> I imagine that depends on how much it costs us - we've been pretty careful
> about binary size growth/minimization/etc for a while now
>

Does this add much size? This only makes strings longer and doesn't force
emission of types, right? (From what I understand, types are what makes
-fline-tables-only output much smaller.) Sorry about the uninformed
question :-) If that's roughly correct though, maybe it'd be good to get an
idea how much bigger debug info would get with qualified names -- we can't
use -fline-tables-only 'cause they make stacks look very bad, and if
qualified names in debug info would give us decent stacks while still being
smaller, that'd be cool. (See also thread "rfc: Adding a mode to
-gline-tables-only to include parameter names, namespaces" from a while
ago.)


> , so it may be worth the tradeoff to say that llvm-symbolizer produces a
> better experience on this extra minimized data.
>
>
>> For CodeView, because the linkage name isn't present anywhere, we can't
>> actually do any better with llvm-symbolizer, and we need the fully scoped
>> name.
>>
>
>
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