Hi Thomas,

On 24/06/2019 01:34, Thomas Gleixner wrote:

Vincenzo,

On Fri, 21 Jun 2019, Vincenzo Frascino wrote:

quoted

vDSO (virtual dynamic shared object) is a mechanism that the Linux
kernel provides as an alternative to system calls to reduce where
possible the costs in terms of cycles.
This is possible because certain syscalls like gettimeofday() do
not write any data and return one or more values that are stored
in the kernel, which makes relatively safe calling them directly
as a library function.

Even if the mechanism is pretty much standard, every architecture
in the last few years ended up implementing their own vDSO library
in the architectural code.

....
 

quoted

This implementation contains the portings to the common library for: arm64,
compat mode for arm64, arm, mips, x86_64, x32, compat mode for x86_64 and
i386.

I picked up the core implementation and the ARM64 and x86 conversion. I did
some refinements in several places, coding style, naming conventions,
comments and changelogs including subject prefixes. Please double check!

I tested your changes and they seem OK
(git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/vdso).

...

As you can see from the commit dates, this has soaked for some time in a
WIP branch and I did extensive regression testing. So far so good.

Thanks a lot for going through several iterations. It's a very much
appreciated effort!

It has been a lot of fun and I learned many many things about the vDSOs and the
kernel that I did not know before. Thanks to you for your patience and guidance.

Especially with the upcoming time namespaces this will avoid a lot of
duplicated and pointlessly different horrors all over the architecture
space. Any architecture which wants to gain that support needs to convert
to the generic VDSO first.

As you have become the dude who knows almost everything about VDSO
including all the nasty pitfalls, I propose the patch below.

Thanks for this, it means a lot to me.

-- 
Regards,
Vincenzo