Tamar Christina <tamar.christ...@arm.com> writes:
> One question I did have not directly related to the unwinder changes,
> But the ABI mentions that if any of the reserved bytes in TPIDR2_EL0
> Block are non-zero that TPIDR2_EL0 must be left unchanged [1].
The full requirement is:
If TPIDR2_EL0 is nonnull and if any reserved byte in the first 16 bytes
of the TPIDR2 block has a nonzero value, the thread must do one of the
following:
* leave TPIDR2_EL0 unchanged;
* abort in some platform-defined manner; or
* handle the nonzero reserved bytes of the TPIDR2 block in accordance
with future versions of the AAPCS64.
So...
> If that's the case what does it mean for the lazy save scheme, since it
> requires that TPIDR2_EL0 be 0 at the end of the save? I see we don't
> actually check that in e.g. __arm_za_disable, we just unconditionally
> zero TPIDR2_EL0.
...we take the second or third option (aborting or handling in line
with a future PCS version). Currently it's always the aborting option,
since there has been no addition to TPIDR2 blocks since their original
definition.
__arm_za_disable is documented as saving in the same way as __arm_tpidr2_save,
and __arm_tpidr2_save is documented as doing:
* If any of the reserved bytes in the first 16 bytes of the TPIDR2
block are nonzero, the subroutine either:
* aborts in some platform-defined manner; or
* handles the nonzero reserved bytes of the TPIDR2 block in
accordance with future versions of the AAPCS64.
Richard
