Em Wed, Jul 12, 2017 at 08:40:57PM +1000, Michael Ellerman escreveu:
> Arnaldo Carvalho de Melo <a...@kernel.org> writes:
>
> > Em Tue, Jul 11, 2017 at 04:38:28PM -0300, Arnaldo Carvalho de Melo escreveu:
> >> Em Tue, Jul 11, 2017 at 04:03:04PM -0300, Arnaldo Carvalho de Melo
> >> escreveu:
> >> > Em Fri, Jul 07, 2017 at 02:17:25PM +0200, Thomas-Mich Richter escreveu:
> >> > > On 07/06/2017 02:35 PM, Thomas-Mich Richter wrote:
> >> > > It determines the kernel starts at address 1<<63 and loads the kernel
> >> > > address mapping.
> >> > > On s390x
> >> > > - The kernel starts at 0x0 (value of map->start) and thus all checks
> >> > > in function
> >> > > thread__find_addr_map() fail and no symbol is found for the
> >> > > specified addresses
> >> > > because the kernel starts at 0x8000000000000000. Which is wrong the
> >> > > kernel start at 0x0.
> >
> >> > Hi Thomas, really nice debugging session!
> >
> >> > I'm trying the one-liner below, Adrian, can you please check this and
> >> > provide an ack? I think that that comment about the address that it will
> >> > default when map__load() fails needs rewriting in light of Thomas
> >> > comments about other arches (see further below)?
> >
> >> > I did a quick check of machine->kernel_start usage in Intel PT and since
> >> > on x86 that assumption about partitioning the address space holds, no
> >> > problem should be introduced by the one-liner fix, right?
> >
> >> Argh, this is also broken:
> >
> >> static inline bool machine__kernel_ip(struct machine *machine, u64 ip)
> >> {
> >> u64 kernel_start = machine__kernel_start(machine);
> >>
> >> return ip >= kernel_start;
> >> }
> >>
> >> We can't judge if a address is in the kernel like that :-\
> >
> > So, this is used by:
> >
> > [acme@jouet linux]$ find tools/ -name "*.[ch]" | xargs grep -w
> > machine__kernel_ip
> > tools/perf/builtin-script.c: kernel = machine__kernel_ip(machine,
> > start);
> > tools/perf/builtin-script.c: if (kernel !=
> > machine__kernel_ip(machine, end)) {
> >
> > That is just for "brstackinsn", would that make sense for Sparc, S/390?
> >
> > tools/perf/util/intel-bts.c: if (machine__kernel_ip(machine, ip))
> > tools/perf/util/intel-bts.c: if
> > (!machine__kernel_ip(btsq->bts->machine, branch->from) &&
> > tools/perf/util/intel-bts.c:
> > machine__kernel_ip(btsq->bts->machine, branch->to) &&
> >
> > Intel specific stuff, so should be ok.
> >
> > tools/perf/util/event.c: machine__kernel_ip(machine,
> > al->addr)) {
> >
> > For this last one, that affects all arches, I think we can just remove
> > this check and look at the kernel when not finding it anywhere else?
> >
> > diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> > index dc5c3bb69d73..8e435baaae6a 100644
> > --- a/tools/perf/util/event.c
> > +++ b/tools/perf/util/event.c
> > @@ -1432,8 +1432,7 @@ void thread__find_addr_map(struct thread *thread, u8
> > cpumode,
> > * in the whole kernel symbol list.
> > */
> > if (cpumode == PERF_RECORD_MISC_USER && machine &&
> > - mg != &machine->kmaps &&
> > - machine__kernel_ip(machine, al->addr)) {
> > + mg != &machine->kmaps) {
> > mg = &machine->kmaps;
> > load_map = true;
> > goto try_again;
>
> Am I reading this right? We have a sample that claims to be in
> userspace, but was not found in any symbol map, so we try looking for it
> in the kernel map.
>
> And the change is that previously we checked if the address was >= (1 << 63),
> whereas after we don't bother.
>
> Seems harmless™.
Thanks, will take that as an Acked-by:, ok?
> cheers
