William Cohen wrote:
On 04/24/2012 07:39 AM, Nicolas Pitre wrote:
On Tue, 24 Apr 2012, Andrew Haley wrote:
On 04/23/2012 09:31 PM, Nicolas Pitre wrote:
On Mon, 23 Apr 2012, Andrew Haley wrote:
On 04/23/2012 06:36 PM, Thomas Meyer wrote:
I'm running the Ubuntun 2.6.38 Tegra2 kernel (because of their fbdev
support) on top of Fedora 17 armv5el on an Toshiba AC100 Laptop. The
rsyslog package crashed everytime because of the missing kernel support
of cmpxchg64. So when relying on the kernel helpers make sure that the
resp. kernel support exists.
Indeed. I had to write a workaround in IcedTea (i.e. java) on ARM for
just this reason. If you can't depend on a kernel helper being there I
can't see it's of any use.
Kernel helpers don't disappear with time. You therefore can probe for
their availability (see the documentation) in case the kernel support
could be backported, or just refuse to run if the kernel version isn't
recent enough. This is not much different from relying on a new
syscall.
Indeed it is. What would I gain from adding such a test? All I can
see is extra complication, untested code paths, and larger programs.
What alternative do you have, other than not using any atomic
operations?
The untested code path is particularly nasty.
How buggy the following code might be:
fprintf(stderr, "Your kernel is too old, aborting\n")
exit(1);
?
Nicolas
Checking kernel characteristics of the running kernel on a Fedora
build system might not be a good idea. The build system might be a
chroot jail on an older release (for example fedora 17 chroot on
fedora 15). This was a problem when building the early versions
of the papi RPMs. RHEL6 build roots were on RHEL5 machines. Checking
the kernel version with a "uname -r" showed a kernel RHEL5 kernel that
didn't have the need perf support. However, things were being built
for a RHEL6 so this test was misleading. Is it possible to get this
information from kernel-headers rather than probing the running kernel?
I am sure I remember having been bitten by this when rebuilding RHEL6
src.rpms on F12/F13 builders but for the life of me I cannot recall
which packages were involved. IMO a builder that isn't the same version
as the distro being built should only ever be used for a bootstrapping
build - otherwise all sorts of anomalies creep in. Having said that, it
is a good idea to hunt down the sources of such anomalies, so from that
point of view, a kernel/distro mismatch on the builders is a good thing
from the point of view of thorough testing.
Gordan
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