.eh_frame augmentation character for MTE stack tagging

Matthew Malcomson matthew.malcomson@arm.com
Mon Jun 6 14:15:09 GMT 2022

Hi there,

Just to mention that this decision has been included in the Arm ABI project.



On 6/6/22 12:00, Richard Earnshaw via Gcc wrote:
> 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.

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