Re: [RFC PATCH 08/10] arm64/sve: ptrace: Wire up vector length control and reporting

On 17-01-12 11:26:07, Dave Martin wrote:
> This patch adds support for manipulating a task's vector length at
> runtime via ptrace.
> 

I hope kernel doesn't provide such interface to ptracer to change vector
length.  The vector length is sort of a read-only property of thread/process/
program to debugger, unless we really have a clear requirement to modify
vector length in debugging.  I may miss something because I haven't debug
SVE code yet.

> As a simplification, we turn the task back into an FPSIMD-only task
> when changing the vector length.  If the register data is written
> too, we then turn the task back into an SVE task, with changed
> task_struct layout for the SVE data, before the actual data writing
> is done.
> 
> Because the vector length is now variable, sve_get() now needs to
> return the real maximum for user_sve_header.max_vl, since .vl may
> be less than this (that's the whole point).
> 

-- 
Yao (齐尧)