[PATCH] D85474: Add -fbinutils-version= to gate ELF features on the specified binutils version

Wed Oct 21 16:22:54 PDT 2020

MaskRay added a comment.

In D85474#2344823 <https://reviews.llvm.org/D85474#2344823>, @compnerd wrote:

> In D85474#2343393 <https://reviews.llvm.org/D85474#2343393>, @MaskRay wrote:
>
>> In D85474#2343356 <https://reviews.llvm.org/D85474#2343356>, @dexonsmith wrote:
>>
>>> In D85474#2343326 <https://reviews.llvm.org/D85474#2343326>, @MaskRay wrote:
>>>
>>>> In D85474#2342365 <https://reviews.llvm.org/D85474#2342365>, @compnerd wrote:
>>>>
>>>>> Is there a reason to not use the existing `-mlinker-version=` option and expanding that beyond just Darwin targets?  I feel like having the same option would be much nicer.
>>>
>>> I agree with @compnerd that it seems better to reuse this if possible. I wasn't around back then, but I have to assume it was named generically in order to enable that.
>>>
>>>> `-mlinker-version` is currently a macOS option. We could reuse it but that would be confusing: when -fuse-ld=lld is specified, does it specify the lld version? (No)
>>>
>>> Maybe it should?
>
> Actually, I think it has to - there is some work underway to add MachO support to lld - so we will need to have this be the lld version anyway in that case.
>
>> Then there is an expanded use case, -fuse-ld= which is just a driver option for linking, will now affect code generation.
>
> I don't see this as an expanded use case - this is precisely the use case it is intended for.  It is specifying the linker - the linker may have a different set of features and code generation (and the driver behaviour) need to adjust for that.  If the linker does not support `.drectve` processing on PE/COFF, it will need to change the code generation.  This seems very much in scope for the option.

This seems to assume the an object file is emitted for one specific linker, a standard system linker or LLD (ELF or Mach-O). How do you communicate the fact that the user wants to emit object files suitable for both the standard system linker and LLD? -fuse-ld=bfd,lld or other variants? This is a much wider design space I somewhat want to avoid. I hope I can see more convincing arguments that -mlinker-version= plus a few other toggles are really better than -fbinutils-version=. I have actually thought about -mlinker-version= when @jyknight or someone else mentioned it. But with more thoughts I don't find it actually better than a very specific -fbinutils-version= which users should immediately know the intention.

>>>> There are also GNU as related issues.
>>>
>>> I don't understand this bit.
>>
>> This is the main point. Many feature are also related to the version of GNU assembler when -fno-integrated-as is specified.
>
> I could also be using a different assembler than binutils, so controlling this via a binutils specific option seems less appealing, and seems better to have the assembler be different from the linker seems better.

So do you suggest an option specifically for assembler? -massembler-version? Then how do you communicate the fact that you want to be compatible with GNU as from binutils?

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D85474/new/

https://reviews.llvm.org/D85474