Messages in this thread | | | Date | Thu, 23 Sep 2021 00:00:11 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH v2] perf test: Fix dwarf unwind for optimized builds. |
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On Wed, Sep 22, 2021 at 10:38:12AM -0700, Ian Rogers wrote: > To ensure the stack frames are on the stack tail calls optimizations > need to be inhibited. If your compiler supports an attribute use it, > otherwise use an asm volatile barrier. > > The barrier fix was suggested here: > https://lore.kernel.org/lkml/20201028081123.GT2628@hirez.programming.kicks-ass.net/ > Tested with an optimized clang build and by forcing the asm barrier > route with an optimized clang build. > > A GCC bug tracking a proper disable_tail_calls is: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97831 > > Fixes: 9ae1e990f1ab ("perf tools: Remove broken __no_tail_call > attribute") > > v2. is a rebase. The original fix patch generated quite a lot of > discussion over the right place for the fix: > https://lore.kernel.org/lkml/20201114000803.909530-1-irogers@google.com/ > The patch reflects my preference of it being near the use, so that > future code cleanups don't break this somewhat special usage.
Acked-by: Jiri Olsa <jolsa@redhat.com>
thanks, jirka
> > Signed-off-by: Ian Rogers <irogers@google.com> > --- > tools/perf/tests/dwarf-unwind.c | 39 +++++++++++++++++++++++++++------ > 1 file changed, 32 insertions(+), 7 deletions(-) > > diff --git a/tools/perf/tests/dwarf-unwind.c b/tools/perf/tests/dwarf-unwind.c > index a288035eb362..c756284b3b13 100644 > --- a/tools/perf/tests/dwarf-unwind.c > +++ b/tools/perf/tests/dwarf-unwind.c > @@ -20,6 +20,23 @@ > /* For bsearch. We try to unwind functions in shared object. */ > #include <stdlib.h> > > +/* > + * The test will assert frames are on the stack but tail call optimizations lose > + * the frame of the caller. Clang can disable this optimization on a called > + * function but GCC currently (11/2020) lacks this attribute. The barrier is > + * used to inhibit tail calls in these cases. > + */ > +#ifdef __has_attribute > +#if __has_attribute(disable_tail_calls) > +#define NO_TAIL_CALL_ATTRIBUTE __attribute__((disable_tail_calls)) > +#define NO_TAIL_CALL_BARRIER > +#endif > +#endif > +#ifndef NO_TAIL_CALL_ATTRIBUTE > +#define NO_TAIL_CALL_ATTRIBUTE > +#define NO_TAIL_CALL_BARRIER __asm__ __volatile__("" : : : "memory"); > +#endif > + > static int mmap_handler(struct perf_tool *tool __maybe_unused, > union perf_event *event, > struct perf_sample *sample, > @@ -91,7 +108,7 @@ static int unwind_entry(struct unwind_entry *entry, void *arg) > return strcmp((const char *) symbol, funcs[idx]); > } > > -noinline int test_dwarf_unwind__thread(struct thread *thread) > +NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__thread(struct thread *thread) > { > struct perf_sample sample; > unsigned long cnt = 0; > @@ -122,7 +139,7 @@ noinline int test_dwarf_unwind__thread(struct thread *thread) > > static int global_unwind_retval = -INT_MAX; > > -noinline int test_dwarf_unwind__compare(void *p1, void *p2) > +NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__compare(void *p1, void *p2) > { > /* Any possible value should be 'thread' */ > struct thread *thread = *(struct thread **)p1; > @@ -141,7 +158,7 @@ noinline int test_dwarf_unwind__compare(void *p1, void *p2) > return p1 - p2; > } > > -noinline int test_dwarf_unwind__krava_3(struct thread *thread) > +NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__krava_3(struct thread *thread) > { > struct thread *array[2] = {thread, thread}; > void *fp = &bsearch; > @@ -160,14 +177,22 @@ noinline int test_dwarf_unwind__krava_3(struct thread *thread) > return global_unwind_retval; > } > > -noinline int test_dwarf_unwind__krava_2(struct thread *thread) > +NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__krava_2(struct thread *thread) > { > - return test_dwarf_unwind__krava_3(thread); > + int ret; > + > + ret = test_dwarf_unwind__krava_3(thread); > + NO_TAIL_CALL_BARRIER; > + return ret; > } > > -noinline int test_dwarf_unwind__krava_1(struct thread *thread) > +NO_TAIL_CALL_ATTRIBUTE noinline int test_dwarf_unwind__krava_1(struct thread *thread) > { > - return test_dwarf_unwind__krava_2(thread); > + int ret; > + > + ret = test_dwarf_unwind__krava_2(thread); > + NO_TAIL_CALL_BARRIER; > + return ret; > } > > int test__dwarf_unwind(struct test *test __maybe_unused, int subtest __maybe_unused) > -- > 2.33.0.464.g1972c5931b-goog >
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