llvm dev - Feb 2014 - [LLVMdev] Target Assembly Parser: Access to Reloc::Model

Some Mips macros (e.g. la[1]) and the handling of Mips directives used for
Position-Independent Programming (e.g. .cpload[2]) require access to
Reloc::Model from within the Assembly Parser but there doesn't seem to be a
way to do it in its current form.
  1) Reloc::Model is passed to MCObjectFileInfo but it's a private member of
that class
  2) TargetMachine is not accessible

I can also see that clang initializes MCObjectFileInfo with Reloc::Default which
isn't entirely right but that's a different matter. I'll come back
to that later after we decide what's the right approach to fix this issue.

Any suggestions about the right way to expose the relocation model to the
assembly parser ?

[1] la - load address. Roughly speaking this macro expands to a GOT access if
generating PIC or to an absolute access if not .
[2] .cpload - This directive sets up $gp (Global Pointer) if PIC or it can be
ignored for the static model.

Regards,
Matheus
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20140225/ac35136f/attachment.html>

Can't this be handled in the Streamer? That way the asm streamer can
just print "la" and ".cpload" and the object streamer
already has the
necessary information.

Cheers,
Rafael


On 25 February 2014 11:31, Matheus Almeida <Matheus.Almeida at imgtec.com>
wrote:
> Some Mips macros (e.g. la[1]) and the handling of Mips directives used for
> Position-Independent Programming (e.g. .cpload[2]) require access to
> Reloc::Model from within the Assembly Parser but there doesn’t seem to be a
> way to do it in its current form.
>
>   1) Reloc::Model is passed to MCObjectFileInfo but it’s a private member
of
> that class
>
>   2) TargetMachine is not accessible
>
>
>
> I can also see that clang initializes MCObjectFileInfo with Reloc::Default
> which isn’t entirely right but that’s a different matter. I’ll come back to
> that later after we decide what’s the right approach to fix this issue.
>
>
>
> Any suggestions about the right way to expose the relocation model to the
> assembly parser ?
>
>
>
> [1] la – load address. Roughly speaking this macro expands to a GOT access
> if generating PIC or to an absolute access if not .
>
> [2] .cpload – This directive sets up $gp (Global Pointer) if PIC or it can
> be ignored for the static model.
>
>
>
> Regards,
>
> Matheus
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

Hi Rafael,

Sure, the expansion of at least .cpload should be done in the Target ELFStreamer
but AFAICS it doesn't solve my initial problem. MCCodeGenInfo is not created
in tools where CodeGen isn't needed (llvm-mc) and it's still not
possible to access the Relocation Model in MCObjectFileInfo from the target
streamer (private member).

Am I missing something obvious ?

There are many ways to work around this issue (some better than others
though...):
1) Store Reloc::Model in MCSubtargetInfo. 
2) Make MCCodeGenInfo accessible from both worlds (CodeGen and all of the MC
layer).
3) Pass Reloc::Model to the Assembly Parser. This could then be passed on to the
streamers without problems because the AsmPrinter also has access to the
relocation model.
4) Use 'friendship' to allow the streamers to access the private members
of MCObjectFileInfo.

Regards,
Matheus

-----Original Message-----
From: Rafael Espíndola [mailto:rafael.espindola at gmail.com] 
Sent: 26 February 2014 23:24
To: Matheus Almeida
Cc: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] Target Assembly Parser: Access to Reloc::Model

Can't this be handled in the Streamer? That way the asm streamer can just
print "la" and ".cpload" and the object streamer already has
the necessary information.

Cheers,
Rafael


On 25 February 2014 11:31, Matheus Almeida <Matheus.Almeida at imgtec.com>
wrote:
> Some Mips macros (e.g. la[1]) and the handling of Mips directives used 
> for Position-Independent Programming (e.g. .cpload[2]) require access 
> to Reloc::Model from within the Assembly Parser but there doesn’t seem 
> to be a way to do it in its current form.
>
>   1) Reloc::Model is passed to MCObjectFileInfo but it’s a private 
> member of that class
>
>   2) TargetMachine is not accessible
>
>
>
> I can also see that clang initializes MCObjectFileInfo with 
> Reloc::Default which isn’t entirely right but that’s a different 
> matter. I’ll come back to that later after we decide what’s the right
approach to fix this issue.
>
>
>
> Any suggestions about the right way to expose the relocation model to 
> the assembly parser ?
>
>
>
> [1] la – load address. Roughly speaking this macro expands to a GOT 
> access if generating PIC or to an absolute access if not .
>
> [2] .cpload – This directive sets up $gp (Global Pointer) if PIC or it 
> can be ignored for the static model.
>
>
>
> Regards,
>
> Matheus
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>