Re: [OE-core] [PATCH] linux-libc-headers: Check for asm/bpf_perf_event.h before multilibbing

["Khem Raj" <raj.khem@gmail.com>]

On Wed, May 27, 2020 at 3:57 PM Khem Raj <raj.khem@gmail.com> wrote:
>
> On Wed, May 27, 2020 at 3:43 PM Andre McCurdy <armccurdy@gmail.com> wrote:
> >
> > On Wed, May 27, 2020 at 2:52 PM Phil Blundell via
> > lists.openembedded.org <pb=pbcl.net@lists.openembedded.org> wrote:
> > >
> > > On Wed, May 27, 2020 at 02:46:24PM -0700, Khem Raj wrote:
> > > > and building userspace against way newer kernel-headers with older
> > > > kernel underneath has unintended
> > > > consequences.
> > >
> > > Can you be more specific?  If this doesn't work, it's just a bug and
> > > should be fixed.  What problems are you having?
> >
> > I don't have an up to date example, but I've been using kernel version
> > specific libc headers for all my projects for many years. The issue
> > which prompted me to do that was run time crashes from libcap-ng and
> > the historical commit message was:
> >
> > ----
> >
> >  linux-libc-headers: use 3.3.8 kernel header files for mips platforms
> >
> >  If libcap-ng is unable to probe kernel capabilities at runtime then
> >  it will assume the kernel supports all features defined by the libc
> >  kernel headers. Since our default libc kernel headers (linux 3.14)
> >  define capabilities which are not available in linux 3.3 based
> >  stblinux kernel used for our MIPS platforms, that causes runtime
> >  crashes.
> >
> >  As a workaround, force an older version of linux-libc-headers for all
> >  MIPS platforms to try to remove that discrepancy between the kernel's
> >  capabilities and those defined in the libc kernel headers.
> >
>
> there are similar issues seen with linput.h using apps. I will dig the reasons
> but it does work when kernel and kernel header. versions are same and its using
> mainlne release for kernel headers here, so there is no vendor specific code
> perhaps that's breaking APIs
>

https://github.com/torvalds/linux/commit/052876f8e5aec887d22c4d06e54aa5531ffcec75

this change e.g. in userspace checks for UINPUT_VERSION and decides to
use one method
or legacy to setup the device but this is really not gonna work with
kernels where these ioctls
are not available, it perhaps can be fixed to not check for
UINPUT_VERSION but then there
could be many such cases, how many can we chase.

> > ----
> >
> > The risk of using bleeding edge linux-libc-headers with an older
> > kernel may be low, it's not zero. Since OE testing doesn't appear to
> > include any coverage of older kernels, I'm not sure why I should be
> > the guinea pig and take the risk!