r205261 - DebugInfo compression: Enable compression before any sections are created.

[David Blaikie]

On Mon, Mar 31, 2014 at 4:35 PM, Eric Christopher <echristo at gmail.com> wrote:
> On Mon, Mar 31, 2014 at 4:13 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> Author: dblaikie
>> Date: Mon Mar 31 18:13:30 2014
>> New Revision: 205261
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=205261&view=rev
>> Log:
>> DebugInfo compression: Enable compression before any sections are created.
>>
>> For those playing at home this produced some fairly subtle behavior. The
>> sections created in InitMCObjectFileInfo were created without compressed
>> debug info (a mistake, but not necessarily /broken). Since these
>> sections were almost always referenced by the existing MCSection object,
>> this almost worked.
>>
>> This got weird when we got to handling the relocations for a section.
>> See ELFObjectWriter::WriteSection where we compute the true section for
>> a relocation section by simply stripping the ".rela" prefix and then
>> looking up that section - doing so hit the compression codepath, looked
>> up .zdebug_blah and found a newly constructed empty section... thus,
>> things got weird.
>>
>> This is untestable without a cross-project test (let me know if people
>> would prefer that to no testing).
>
> *blink* Wow.
>
> I think the only way to do this is via projects/test-suite and ... I
> think I'm ok not, but ick.

Yeah, fair point. It'd be nice if we just had a sanctioned bucket of
cross-project tests that didn't involve quite so many layers of crufty
execution garbage as the test-suite...

>
>> +  if (Opts.CompressDebugSections)
>> +    MAI->setCompressDebugSections(true);
>>
>
> Please comment why on earth this has to be here, otherwise someone
> might try to move it.

Comment added in r205265.