[PATCH v2 07/12] powerpc/ptrace: Expose DEXCR and HDEXCR registers to ptrace

Russell Currey ruscur at russell.cc
Mon May 8 14:30:26 AEST 2023

On Thu, 2023-03-30 at 16:50 +1100, Benjamin Gray wrote:
> The DEXCR register is of interest when ptracing processes. Currently
> it
> is static, but eventually will be dynamically controllable by a
> process.
> If a process can control its own, then it is useful for it to be
> ptrace-able to (e.g., for checkpoint-restore functionality).
> It is also relevant to core dumps (the NPHIE aspect in particular),
> which use the ptrace mechanism (or is it the other way around?) to
> decide what to dump. The HDEXCR is useful here too, as the NPHIE
> aspect
> may be set in the HDEXCR without being set in the DEXCR. Although the
> HDEXCR is per-cpu and we don't track it in the task struct (it's
> useless
> in normal operation), it would be difficult to imagine why a
> hypervisor
> would set it to different values within a guest. A hypervisor cannot
> safely set NPHIE differently at least, as that would break programs.
> Expose a read-only view of the userspace DEXCR and HDEXCR to ptrace.
> The HDEXCR is always readonly, and is useful for diagnosing the core
> dumps (as the HDEXCR may set NPHIE without the DEXCR setting it).
> Signed-off-by: Benjamin Gray <bgray at linux.ibm.com>

I don't know much about ptrace but this looks sane.

Reviewed-by: Russell Currey <ruscur at russell.cc>

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