Re: [PATCH 3/3] kbuild: introduce KERNEL_VERSION2 and LINUX_VERSION_CODE2

[Sasha Levin]

On Sat, Feb 06, 2021 at 09:45:44PM +0900, Masahiro Yamada wrote:
> On Sat, Feb 6, 2021 at 12:50 PM Sasha Levin <sashal@xxxxxxxxxx> wrote:
> > -       ((c) > 255 ? 255 : (c)))'
> > +       ((c) > 255 ? 255 : (c)))';                                       \
> > +       echo \#define LINUX_VERSION_CODE2 $(shell                        \
> > +       expr $(VERSION) \* 16777216 + 0$(PATCHLEVEL) \* 65536 + 0$(SUBLEVEL)); \
>
>
> Is this needed?
> No one in this patch uses LINUX_VERSION_CODE2.
>
> The in-kernel code can use
> LINUX_VERSION_MAJOR/PATCHLEVEL/SUBLEVEL directly.
>
>
> Userspace does not need LINUX_VERSION_CODE2 either.
>
> Your comment in 2/3 states that
> userspace only decodes MAJOR and PATCHLEVEL fields,
> so LINUX_VERSION_CODE will still do well.

Yes, that's fair. I wanted to have that to make it easy for out of tree
code to handle in-kernel ABI changes but as we don't care about such
code there's no strict need for LINUX_VERSION_CODE2. I'll drop it.

> > index ab4b98b3165db..a56bf381335e9 100644
> > --- a/tools/perf/tests/bpf-script-example.c
> > +++ b/tools/perf/tests/bpf-script-example.c
> > @@ -5,7 +5,7 @@
> >   */
> >  #ifndef LINUX_VERSION_CODE
> >  # error Need LINUX_VERSION_CODE
> > -# error Example: for 4.2 kernel, put 'clang-opt="-DLINUX_VERSION_CODE=0x40200" into llvm section of ~/.perfconfig'
> > +# error Example: for 4.2 kernel, put 'clang-opt="-DLINUX_VERSION_CODE=0x4020000" into llvm section of ~/.perfconfig'
>
>
> Is this change needed?

Good point, no. I'll resend.

--
Thanks,
Sasha