Re: perf report does not resolve symbols on s390x

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

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;

> > > This raises 2 questions:
> > > 1. s390 has a 64 bit address space for user and kernel. The processor status word (PSW)
> > >    determines which address space to use. That requires the PSW in the sample. Not sure
> > >    this is the case?
> > > 2. How does this work on sparc and other architectures with the same addressing scheme?
> > >
> > > Thanks.
> > > --
> > > Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany