[cfe-dev] rfc: Adding a mode to -gline-tables-only to include parameter names, namespaces

[Eric Christopher]

On Wed, Apr 29, 2015 at 1:33 PM Adrian Prantl <aprantl at apple.com> wrote:

> On Apr 29, 2015, at 1:30 PM, Nico Weber <thakis at chromium.org> wrote:
>
> On Wed, Apr 29, 2015 at 1:25 PM, Adrian Prantl <aprantl at apple.com> wrote:
>
>>
>> On Apr 29, 2015, at 1:03 PM, Adrian Prantl <aprantl at apple.com> wrote:
>>
>>
>> On Apr 29, 2015, at 12:25 PM, Nico Weber <thakis at chromium.org> wrote:
>>
>> Hi,
>>
>> the motivation for -gline-tables-only was to make debug info much
>> smaller, but still include enough to get usable stack frames [1]. We
>> recently tried using it in Chromium and discovered that the stack frames
>> aren't all that usable: Function parameters disappear, as do function
>> namespaces.
>>
>> Are there any concerns about adding a mode to -gline-tables-only (or a
>> second flag -gline-tables-full, or similar) that includes function
>> parameter info and namespace info but still omits most debug info?
>>
>>
>> I’m not convinced that the resulting debug info will dramatically smaller
>> than the full debug info. The largest bit of the debug info is the type
>> information if we are going to emit function parameters that will probably
>> pull in the majority of the types in the program.
>>
>>
>> (Background: We rely on dsym files to let our crash server symbolize
>> crash dumps we get from the wild. dsymutil uses debug info, but it
>> apparently crashes if debug info is > 4GB.
>>
>>
>> The problem here is that neither llvm nor dsymutil understand the 64-bit
>> DWARF format. Note that the llvm-dsymutil that is being developed will be
>> able to do ODR-based type uniquing for C++, which should also provide
>> enough savings to make this go well under the 4GB mark.
>>
>>
>> As a stopgap until all of Fred’s patches are in, you could also try
>> building with -fstandalone-debug.
>>
>
> Isn't that on by default on Darwin?
>
>
> It is of course. I meant to say -fno-standalone-debug.
>

... as I did the same thing Adrian did. :)

-eric


>
>
>
>> It will make LLDB unhappy but the result will still be much better than
>> 0-line-tables-only.
>>
>
>
>> -- adrian
>>
>>
>> We hit that recently. So we started using -gline-tables-only, but now all
>> our stacks are close to unusable, even though the motivation
>> for gline-tables-only was to still have usable stacks. We can't easily use
>> symbol names as they get stripped very early in our pipeline, and changing
>> that is apparently involved.)
>>
>>
>>
>> -- adrian
>>
>>
>> Thanks,
>> Nico
>>
>>
>> 1:
>> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20120423/056674.html
>>
>>
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>>
>>
>>
>
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