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Subject: Re: .eh_frame augmentation character for MTE stack tagging
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To: Florian Mayer <fmayer@google.com>, gcc@gcc.gnu.org
Cc: Fangrui Song <maskray@google.com>, Evgenii Stepanov <eugenis@google.com>
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On 04/06/2022 00:52, Florian Mayer via Gcc wrote:
> Hey!
> 
> We are in the process of implementing MTE (Memory Tagging Extension)
> stack tagging in LLVM. To support stack tagging in combination with
> exceptions, we need to make sure that the unwinder will untag stack
> frames, to avoid leaving behind stale tags. As such, we need some way
> to communicate to the unwinder to do that.
> 
> In a discussion on llvm-dev [1], it was decided the best way to go
> forward with this would be to add a new character ('G' for taG, as the
> MTE instructions stg etc.) to the eh_frame augmentation string, and
> then handle that in libunwind by clearing the tags of the respective
> frame.
> 
> How does that sound? Would that be a good course of action for GCC as well?
> 
> Thanks,
> Florian
> 
> [1]: https://lists.llvm.org/pipermail/llvm-dev/2020-May/141345.html

Hi Florian,

This is something that needs to be specified in the ABI, not just agreed 
between a couple of compilers. So while the community input is helpful, 
it isn't enough.

The correct place to do this is in the ABI project here: 
https://github.com/ARM-software/abi-aa

R.