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Date: Thu, 23 Sep 2021 10:32:13 -0300 From: Arnaldo Carvalho de Melo <acme@...nel.org> To: Jiri Olsa <jolsa@...hat.com> Cc: Ian Rogers <irogers@...gle.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Mark Rutland <mark.rutland@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Namhyung Kim <namhyung@...nel.org>, linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com, Ard Biesheuvel <ardb@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, Stephane Eranian <eranian@...gle.com> Subject: Re: [PATCH v2] perf test: Fix dwarf unwind for optimized builds. Em Thu, Sep 23, 2021 at 12:00:11AM +0200, Jiri Olsa escreveu: > 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@...hat.com> Thanks, applied. - Arnaldo > thanks, > jirka > > > > > Signed-off-by: Ian Rogers <irogers@...gle.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 > > -- - Arnaldo
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