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Re: [RFC PATCH 07/10] arm64/sve: Add vector length inheritance control
- 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 12:27:55 +0000
- Subject: Re: [RFC PATCH 07/10] arm64/sve: Add vector length inheritance control
- Authentication-results: sourceware.org; auth=none
- References: <1484220369-23970-1-git-send-email-Dave.Martin@arm.com> <1484220369-23970-8-git-send-email-Dave.Martin@arm.com>
On 17-01-12 11:26:06, Dave Martin wrote:
> Currently the vector length is inherited across both fork() and
> exec().
>
> Inheritance across fork() is desirable both for creating a copy of
> a process (traditional fork) or creating a thread (where we want
> all threads to share the same VL by default).
>
> Inheritance across exec() is less desirable, because of the ABI
> impact of large vector lengths on the size of the signal frame --
> when running a new binary, there is no guarantee that the new
> binary is compatible with these ABI changes.
>
> This flag makes the vector length non-inherited by default.
Can we make vector length inherited across fork but non-inherited
across exec by default?
> Instead, the vector length is reset to a system default value,
> unless the THREAD_VL_INHERIT flag has been set for the thread.
>
> THREAD_VL_INHERIT is currently sticky: i.e., if set, it gets
> inherited too. This behaviour may be refined in future if it is
> not flexible enough.
>
--
Yao (齐尧)