Re: [RFC] <sys/tagged-address.h>: An API for tagged address

["H.J. Lu" <hjl.tools@gmail.com>]

On Fri, Feb 12, 2021 at 1:43 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu via Libc-alpha:
>
> > On Thu, Feb 11, 2021 at 12:28 PM Joseph Myers <joseph@codesourcery.com> wrote:
> >>
> >> On Thu, 11 Feb 2021, H.J. Lu via Libc-alpha wrote:
> >>
> >> > An API for tagged address:
> >>
> >> Please write a longer commit message, discussing what "tagged address" is,
> >> which architectures have such a thing (the API should try to cover
> >> whatever is common between architectures as far as possible - is this
> >> meant to relate to AArch64 MTE, how does it relate to the MTE code we
> >
> > This API is for Intel LAM:
> >
> > https://www.phoronix.com/scan.php?page=news_item&px=Intel-LAM-Glibc#:~:text=Intel%20Linear%20Address%20Masking%20(LAM,bit%20linear%20addresses%20for%20metadata.&text=With%20LAM%20enabled%2C%20the%20processor,linear%20address%20to%20access%20memory.
> >
> > and ARM TBI:
> >
> > https://en.wikichip.org/wiki/arm/tbi
>
> Do the setters/getters change process or thread properties?

On x86-64, mask is stored in TCB.   TCB will be updated.  It applies
to all threads.

> The interface assumes that the tag bits are uniform across pointer
> types.  I think that's not true, at least from a historical perspective.

This is true for LAM and TBI.

> People complained that our protection key interfaces are too slow to be
> useful.  Do we need to find a way to inline the tag/untag operations?
>

The internal interface is inlined.  We can also inline the public interface
if needed.  But set_tagged_address_mask isn't inlined at all.

-- 
H.J.