Re: [PATCH v6 1/1] <sys/tagged-address.h>: An API for tagged address

[Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>]

* H. J. Lu:

> By default, the number of the address bits used in address translation
> is the number of address bits.  But it can be changed by ARM Top-byte
> Ignore (TBI) or Intel Linear Address Masking (LAM).

I think the fundamental concern is that we don't really know today how
this API would be used.  Szabolcs has said that Arm doesn't need this
API for HWSAN.  TBI has already other (incompatible) users, I think.
(Although OpenJDK's ZGC garbage collector has moved off it.)

My concern is that this interface essentialyl sets in stone a certain
programming model for LAM, and we really don't know today if that's the
right approach.

I also expect that HWSAN needs to poke at glibc internals, like the
other sanitizers, so I don't see why calling a kernel API behind glibc's
back would be problematic.

As a side effect of the libpthread merge, we freed DF_1_INITFIRST for
other uses, so you should be able to work around initialization ordering
issues, too.

Thanks,
Florian