[llvm-commits] Proof of concept patch for unifying the .s/ELF emission of .ARM.attributes

[Jason Kim]

Hi everyone, please find enclosed updated version of arm-mc-elf-s05.patch.

On Mon, Oct 11, 2010 at 10:39 AM, Jason Kim <jasonwkim at google.com> wrote:
> On Mon, Oct 11, 2010 at 9:20 AM, Jim Grosbach <grosbach at apple.com> wrote:
>> Hi Jason,
>>
>> Glad to see this making progress. Here's a bit of general feedback. I'm not an expert on Linux ELF, so I can't really comment on that aspect of things, though.
>>
>>>  namespace ARMBuildAttrs {
>>>    enum AttrType {
>>> +    // For the .cpu asm construct
>>> +    ARM_CPU,
>>> +    // Rest correspond to ELF/.ARM.attributes
>>>      File                      = 1,
>>>      Section                   = 2,
>>>      Symbol                    = 3,
>>
>>
>> Is this new attr distinct from the ones already there for the CPU? CPU_name, in particular, seems a likely candidate. It's hard to tell since the uses of the others don't appear to be implemented yet. In any case, if a new attr does need to be added, it should be consistent with the rest of them. No prefix, and just add the value onto the end (i.e., "Cpu = 71") of the list.
>
> All of the other enums in the ARMBuildAttrs are specific part of (i.e.
> can appear as markers in) the .ARM.attributes section.
> The new one I added correspond to the .cpu asm attr, which translates
> into one or more sequence of CPU_NAME, CPU_ARCH ... in the actual ELF
> section, so I needed a way to get that done.
> There is no neat correspondence between the asm attrs and what goes
> into the .ARM.attributes. Certainly not for the .cpu attribute (its
> one to many)
>

Jim, it turns out that the bulk of the attr emission is driven by a
bunch of bool flags from TargetMachine.
The individual ARMBuildAttrs::AttrType flags are not selected individually,
so there wasn't a real use for the llvm style switch except for the
new flag I added.  (please see new comments in patch)

<cut>
>
> p.s. I have another patch waiting for this to land - I will be adding
> just enough to get a basic two instruction function (thanks for new
> scaffolding on EncodeInstuction()  Jim!)  output as ELF .o, and be
> somewhat sane -
> i.e. ARM/MC/ELF hello world ("misspelled, and broken" but at least it
> will be a start. :-)
>
>
>>
>> Regards,
>>
>>  Jim
>>
>>
>>
>> On Oct 7, 2010, at 8:54 PM, Jason Kim wrote:
>>
>>> Second set of ARM/MC/ELF changes.
>>>
>>> Added ARM specific ELF section types.
>>> Added AttributesSection to ARMElfTargetObject
>>> First step in unifying .cpu assembly tag with ELF/.o
>>> llc now asserts on actual ELF emission on -filetype=obj :-)
>>>
>>> Feedback, please!
>>>
>>> Thanks for reading!
>>>
>>> -Jason
>>> <arm-mc-elf-s05.patch>
>>
>>
>

Unless there is strong objection, I'd like to land this patch soon
(today if possible).
Thanks for reading!!

-jason
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