[RFC PATCH 07/10] arm64/sve: Add vector length inheritance control

[Yao Qi]

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)