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Re: [RFC PATCH 08/10] arm64/sve: ptrace: Wire up vector length control and reporting
- From: Yao Qi <qiyaoltc at gmail dot com>
- To: Dave Martin <Dave dot Martin at arm dot com>
- Cc: linux-arm-kernel at lists dot infradead dot org, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Marc Zyngier <Marc dot Zyngier at arm dot com>, Alan Hayward <alan dot hayward at arm dot com>, Christoffer Dall <christoffer dot dall at linaro dot org>, linux-arch at vger dot kernel dot org, libc-alpha at sourceware dot org, Florian Weimer <fweimer at redhat dot com>, Joseph Myers <joseph at codesourcery dot com>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, Torvald Riegel <triegel at redhat dot com>, gdb at sourceware dot org
- Date: Mon, 16 Jan 2017 12:20:38 +0000
- Subject: Re: [RFC PATCH 08/10] arm64/sve: ptrace: Wire up vector length control and reporting
- Authentication-results: sourceware.org; auth=none
- References: <1484220369-23970-1-git-send-email-Dave.Martin@arm.com> <1484220369-23970-9-git-send-email-Dave.Martin@arm.com>
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)