Re: [PATCH 1/1] perf tool: fix handling NULL al->maps returned from thread__find_map

Casey Chen
2024-07-10T22:29:39Z

On Mon, Jul 8, 2024 at 10:01 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> Hello,
>
> On Mon, Jul 8, 2024 at 4:23 PM Casey Chen <cachen@purestorage.com> wrote:
> >
> > With 0dd5041c9a0e ("perf addr_location: Add init/exit/copy functions"),
> > thread__find_map() would return with al->maps or al->map being NULL
> > when cpumode is 3 (macro PERF_RECORD_MISC_HYPERVISOR),
> > later deferencing on it would crash.
> >
> > Fix callers of thread__find_map() or thread__find_symbol() to handle
> > this.
>
> It looks like you drop the callchain if it doesn't find a map/symbol.
> Can we keep the entries with raw hex numbers instead?
>
In add_callchain_ip(), my change let it return if either al.maps is
NULL or al.map is NULL after thread__find_symbol(), I'm not sure what
else can add_callchain_ip() could do to keep raw hex numbers. If it
proceeds, al.sym is NULL, the code inside 'if (al.sym != NULL)' would
skip. callchain_srcline() would return NULL. chain_cursor_append()
would append a node whose ms.maps/ ms.map are NULL. Later
dereferencing them would cause trouble. But we could add other
information to the node, like ip, branch, nr_loop_iter, iter_cycles,
branch_from, are these information good to have ? but how to avoid
dereferencing NULL maps/map later.

Thanks
Casey

> Thanks,
> Namhyung
>
> > ---
> > tools/perf/arch/powerpc/util/skip-callchain-idx.c | 10 ++++++----
> > tools/perf/util/machine.c | 5 +++++
> > tools/perf/util/unwind-libdw.c | 6 ++++--
> > 3 files changed, 15 insertions(+), 6 deletions(-)
> >
> > diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
> > index 5f3edb3004d8..25b0804df4c4 100644
> > --- a/tools/perf/arch/powerpc/util/skip-callchain-idx.c
> > +++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
> > @@ -255,13 +255,14 @@ int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain)
> >
> > thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);
> >
> > - if (al.map)
> > - dso = map__dso(al.map);
> > + if (!al.map)
> > + goto out;
> > +
> > + dso = map__dso(al.map);
> >
> > if (!dso) {
> > pr_debug("%" PRIx64 " dso is NULL\n", ip);
> > - addr_location__exit(&al);
> > - return skip_slot;
> > + goto out;
> > }
> >
> > rc = check_return_addr(dso, map__start(al.map), ip);
> > @@ -282,6 +283,7 @@ int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain)
> > skip_slot = 3;
> > }
> >
> > +out:
> > addr_location__exit(&al);
> > return skip_slot;
> > }
> > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > index 8477edefc299..fa4037d7f3d4 100644
> > --- a/tools/perf/util/machine.c
> > +++ b/tools/perf/util/machine.c
> > @@ -2098,7 +2098,12 @@ static int add_callchain_ip(struct thread *thread,
> > }
> > goto out;
> > }
> > +
> > thread__find_symbol(thread, *cpumode, ip, &al);
> > + if (!al.maps || !al.map) {
> > + err = 1;
> > + goto out;
> > + }
> > }
> >
> > if (al.sym != NULL) {
> > diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
> > index b38d322734b4..fb038ef55be2 100644
> > --- a/tools/perf/util/unwind-libdw.c
> > +++ b/tools/perf/util/unwind-libdw.c
> > @@ -53,8 +53,10 @@ static int __report_module(struct addr_location *al, u64 ip,
> > */
> > thread__find_symbol(ui->thread, PERF_RECORD_MISC_USER, ip, al);
> >
> > - if (al->map)
> > - dso = map__dso(al->map);
> > + if (!al->map)
> > + return -1;
> > +
> > + dso = map__dso(al->map);
> >
> > if (!dso)
> > return 0;
> > --
> > 2.45.2
> >
> >