[PATCH v12 22/40] arm64/sme: Implement ptrace support for streaming mode SVE registers

[Catalin Marinas]

On Fri, Feb 25, 2022 at 04:59:05PM +0000, Mark Brown wrote:
> The streaming mode SVE registers are represented using the same data
> structures as for SVE but since the vector lengths supported and in use
> may not be the same as SVE we represent them with a new type NT_ARM_SSVE.
> Unfortunately we only have a single 16 bit reserved field available in
> the header so there is no space to fit the current and maximum vector
> length for both standard and streaming SVE mode without redefining the
> structure in a way the creates a complicatd and fragile ABI. Since FFR
> is not present in streaming mode it is read and written as zero.
> 
> Setting NT_ARM_SSVE registers will put the task into streaming mode,
> similarly setting NT_ARM_SVE registers will exit it. Reads that do not
> correspond to the current mode of the task will return the header with
> no register data. For compatibility reasons on write setting no flag for
> the register type will be interpreted as setting SVE registers, though
> users can provide no register data as an alternative mechanism for doing
> so.
> 
> Signed-off-by: Mark Brown <broonie at kernel.org>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>