[llvm] r189315 - Move everything depending on Object/MachOFormat.h over to Support/MachO.h.

[David Fang]

Hi all,
 	Did you have more details about the big-endian failures?  Was it 
by chance hello-reloc.s, which tests powerpc-darwin8?  I 
contributed the PPCMachObjectWriter, which has some notes about funny 
endianness in makeRelocationInfo and makeScatteredRelocationInfo.
If you have further revisions of this patch that you'd like tested on 
PowerPC-darwin, I'll be happy to help test.

Fang

> On Aug 27, 2013, at 4:59 PM, Nick Kledzik wrote:
>
>> On Aug 26, 2013, at 10:41 PM, Charles Davis <cdavis5x at gmail.com> wrote:
>>> On Aug 26, 2013, at 11:32 PM, Charles Davis wrote:
>>>> On Aug 26, 2013, at 11:19 PM, David Blaikie wrote:
>>>>
>>>>> On Mon, Aug 26, 2013 at 10:00 PM, Charles Davis <cdavis5x at gmail.com> wrote:
>>>>>> Author: cdavis
>>>>>> Date: Tue Aug 27 00:00:43 2013
>>>>>> New Revision: 189315
>>>>>>
>>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=189315&view=rev
>>>>>> Log:
>>>>>> Move everything depending on Object/MachOFormat.h over to Support/MachO.h.
>>>>>
>>>>> There seem to be a number of unrelated changes in this patch -
>>>>> especially for such a large change, please commit the mechanical
>>>>> portion separately from any other cleanup/changes.
>>>> Sorry. Would you like me to revert this particular change?
>>> I went ahead and reverted it (and r189319) in r189321. It looks like it also broke the tests on some platforms (specifically System z and PowerPC--endianness issue? I don't have a big endian machine to test with, so?).
>>
>> Chip,
>>
>> After looking at the failures, the problematic area is with defining relocation_info using bit fields.  Your patch uses:
>>
>> +    struct scattered_relocation_info {
>> +#if defined(BYTE_ORDER) && defined(BIG_ENDIAN) && (BYTE_ORDER == BIG_ENDIAN)
>> +      uint32_t r_scattered:1,
>> +               r_pcrel:1,
>> +               r_length:2,
>> +               r_type:4,
>> +               r_address:24;
>> +#else
>> +      uint32_t r_address:24,
>> +               r_type:4,
>> +               r_length:2,
>> +               r_pcrel:1,
>> +               r_scattered:1;
>> +#endif
>> +      int32_t r_value;
>> +    };
>>
>>
>> But whether all three of those preprocessor symbols (e.g. BIG_ENDIAN) are set up is hazy.  My guess is one of the is not set up on the failing big endian builders and causing the relocations to be messed up.
> Really? I thought it was because the other struct (relocation_info) *doesn't* use them. So now the order of the bitfields depends on the host endianness--which, when we're making an object file, means that the correct order also depends on the *target* endianness. Unfortunately, we're stuck with this, because the definition was cribbed from <mach-o/reloc.h>, and it has the same problem. (The definition of scattered_relocation_info was also cribbed from <mach-o/reloc.h>; that's why I used the endianness macros there. In fact, I believe I originally used Apple's __BIG_ENDIAN__ macro for this, but I changed it because I figured this wouldn't get defined everywhere it needed to be.) As far as I could tell, the relocations that came out wrong on those machines were plain relocations, not scattered relocations. In particular, several x86_64 relocations came out wrong, and x86_64 doesn't use scattered relocations at all.
>>  I don?t see many of the endian conditionals used anywhere in LLVM.  I?d suggest keeping the MC stuff using the word0 and word1 style of access and avoid using bitfields.
> I figured you'd say that, and it sounds like a good idea regardless: it worked before, after all ;). (It just took me some time to audit my change and make sure there was nothing beyond mechanical renaming so nothing else like this happens.)
>
> New patch attached. In addition to continuing to use MachO::any_relocation_info, it also incorporates David's warning fix from r189319. I don't want to cause any more churn than I already have, so I won't commit until someone goes over it and gives me their LG.
>
> Chip
>

-- 
David Fang
http://www.csl.cornell.edu/~fang/