Re: perf BPF/elfdep intermitent build problems

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Thu, Nov 19, 2015 at 10:29:07AM +0800, Wangnan (F) escreveu:
> On 2015/11/19 10:21, Wangnan (F) wrote:
> >On 2015/11/19 9:24, Wangnan (F) wrote:
> >>On 2015/11/19 6:44, Arnaldo Carvalho de Melo wrote:
> >>>Have you guys ever saw this?
> >>>
> >>>[acme@zoo linux]$ alias m
> >>>alias m='perf stat -e cycles make O=/tmp/build/perf -C tools/perf
> >>>install-bin'
> >>>[acme @zoo linux]$ m
> >>>make: Entering directory '/home/git/linux/tools/perf'
> >>>   BUILD:   Doing 'make -j4' parallel build
> >>>make[2]: Nothing to be done for 'fixdep'.
> >>>   CC       /tmp/build/perf/util/machine.o
> >>>   LD       /tmp/build/perf/util/libperf-in.o
> >>>No libelf found
> >>>BPF API too old
> >>
> >>This error message means the kernel header in rootfs is too old,
> >>causes tools/build/feature/test-bpf.c failed to be built.
> >
> >Strange... even in feature detection it should check BPF API through
> >kernel source where you are using to build perf...
> >
> >I guess you are not using NFS or share it with other people?

Some build problem just happened and your question came to my mind,
yeah, sometimes I NFS mount it from a RHEL6 (and other distros) to do
'make -C tools/perf build-test' to check it works with those distros,
and I forgot to do a:

  make -C tools/ clean

I guess I'll have to try to make build-test support O=... So that
polluting the source tree doesn't causes problems like this.

Will try even to make it turn the source tree read only so that we spot 
when O= is not being honoured...

- Arnaldo