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Date: Wed, 13 Sep 2023 09:34:13 -0700
From: Ian Rogers <irogers@...gle.com>
To: James Clark <james.clark@....com>
Cc: linux-perf-users@...r.kernel.org, acme@...nel.org,
John Garry <john.g.garry@...cle.com>,
Will Deacon <will@...nel.org>,
Mike Leach <mike.leach@...aro.org>,
Leo Yan <leo.yan@...aro.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Kan Liang <kan.liang@...ux.intel.com>,
Haixin Yu <yuhaixin.yhx@...ux.alibaba.com>,
Jing Zhang <renyu.zj@...ux.alibaba.com>,
Eduard Zingerman <eddyz87@...il.com>,
Ravi Bangoria <ravi.bangoria@....com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] perf pmu: Move pmu__find_core_pmu() to pmus.c
On Wed, Sep 13, 2023 at 8:34 AM James Clark <james.clark@....com> wrote:
>
> pmu__find_core_pmu() more logically belongs in pmus.c because it
> iterates over all PMUs, so move it to pmus.c
>
> At the same time rename it to perf_pmus__find_core_pmu() to match the
> naming convention in this file.
>
> list_prepare_entry() can't be used in perf_pmus__scan_core() anymore now
> that it's called from the same compilation unit. This is with -O2
> (specifically -O1 -ftree-vrp -finline-functions
> -finline-small-functions) which allow the bounds of the array
> access to be determined at compile time. list_prepare_entry() subtracts
> the offset of the 'list' member in struct perf_pmu from &core_pmus,
> which isn't a struct perf_pmu. The compiler sees that pmu results in
> &core_pmus - 8 and refuses to compile. At runtime this works because
> list_for_each_entry_continue() always adds the offset back again before
> dereferencing ->next, but it's technically undefined behavior. With
> -fsanitize=undefined an additional warning is generated.
>
> Using list_first_entry_or_null() to get the first entry here avoids
> doing &core_pmus - 8 but has the same result and fixes both the compile
> warning and the undefined behavior warning. There are other uses of
> list_prepare_entry() in pmus.c, but the compiler doesn't seem to be
> able to see that they can also be called with &core_pmus, so I won't
> change any at this time.
>
> Signed-off-by: James Clark <james.clark@....com>
Reviewed-by: Ian Rogers <irogers@...gle.com>
Thanks,
Ian
> ---
> tools/perf/arch/arm64/util/pmu.c | 6 +++---
> tools/perf/tests/expr.c | 2 +-
> tools/perf/util/expr.c | 2 +-
> tools/perf/util/pmu.c | 17 -----------------
> tools/perf/util/pmu.h | 2 +-
> tools/perf/util/pmus.c | 20 +++++++++++++++++++-
> 6 files changed, 25 insertions(+), 24 deletions(-)
>
> diff --git a/tools/perf/arch/arm64/util/pmu.c b/tools/perf/arch/arm64/util/pmu.c
> index 615084eb88d8..3d9330feebd2 100644
> --- a/tools/perf/arch/arm64/util/pmu.c
> +++ b/tools/perf/arch/arm64/util/pmu.c
> @@ -10,7 +10,7 @@
>
> const struct pmu_metrics_table *pmu_metrics_table__find(void)
> {
> - struct perf_pmu *pmu = pmu__find_core_pmu();
> + struct perf_pmu *pmu = perf_pmus__find_core_pmu();
>
> if (pmu)
> return perf_pmu__find_metrics_table(pmu);
> @@ -20,7 +20,7 @@ const struct pmu_metrics_table *pmu_metrics_table__find(void)
>
> const struct pmu_events_table *pmu_events_table__find(void)
> {
> - struct perf_pmu *pmu = pmu__find_core_pmu();
> + struct perf_pmu *pmu = perf_pmus__find_core_pmu();
>
> if (pmu)
> return perf_pmu__find_events_table(pmu);
> @@ -32,7 +32,7 @@ double perf_pmu__cpu_slots_per_cycle(void)
> {
> char path[PATH_MAX];
> unsigned long long slots = 0;
> - struct perf_pmu *pmu = pmu__find_core_pmu();
> + struct perf_pmu *pmu = perf_pmus__find_core_pmu();
>
> if (pmu) {
> perf_pmu__pathname_scnprintf(path, sizeof(path),
> diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
> index 78544092ef0c..e3aa9d4fcf3a 100644
> --- a/tools/perf/tests/expr.c
> +++ b/tools/perf/tests/expr.c
> @@ -76,7 +76,7 @@ static int test__expr(struct test_suite *t __maybe_unused, int subtest __maybe_u
> struct expr_parse_ctx *ctx;
> bool is_intel = false;
> char strcmp_cpuid_buf[256];
> - struct perf_pmu *pmu = pmu__find_core_pmu();
> + struct perf_pmu *pmu = perf_pmus__find_core_pmu();
> char *cpuid = perf_pmu__getcpuid(pmu);
> char *escaped_cpuid1, *escaped_cpuid2;
>
> diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
> index 4488f306de78..7be23b3ac082 100644
> --- a/tools/perf/util/expr.c
> +++ b/tools/perf/util/expr.c
> @@ -509,7 +509,7 @@ double expr__strcmp_cpuid_str(const struct expr_parse_ctx *ctx __maybe_unused,
> bool compute_ids __maybe_unused, const char *test_id)
> {
> double ret;
> - struct perf_pmu *pmu = pmu__find_core_pmu();
> + struct perf_pmu *pmu = perf_pmus__find_core_pmu();
> char *cpuid = perf_pmu__getcpuid(pmu);
>
> if (!cpuid)
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index e2159854ab26..f50a5636633f 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -2050,20 +2050,3 @@ void perf_pmu__delete(struct perf_pmu *pmu)
> zfree(&pmu->id);
> free(pmu);
> }
> -
> -struct perf_pmu *pmu__find_core_pmu(void)
> -{
> - struct perf_pmu *pmu = NULL;
> -
> - while ((pmu = perf_pmus__scan_core(pmu))) {
> - /*
> - * The cpumap should cover all CPUs. Otherwise, some CPUs may
> - * not support some events or have different event IDs.
> - */
> - if (RC_CHK_ACCESS(pmu->cpus)->nr != cpu__max_cpu().cpu)
> - return NULL;
> -
> - return pmu;
> - }
> - return NULL;
> -}
> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
> index bd5d804a6736..d7b46085642d 100644
> --- a/tools/perf/util/pmu.h
> +++ b/tools/perf/util/pmu.h
> @@ -264,6 +264,6 @@ int perf_pmu__pathname_fd(int dirfd, const char *pmu_name, const char *filename,
> struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char *lookup_name);
> struct perf_pmu *perf_pmu__create_placeholder_core_pmu(struct list_head *core_pmus);
> void perf_pmu__delete(struct perf_pmu *pmu);
> -struct perf_pmu *pmu__find_core_pmu(void);
> +struct perf_pmu *perf_pmus__find_core_pmu(void);
>
> #endif /* __PMU_H */
> diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
> index 6631367c756f..cec869cbe163 100644
> --- a/tools/perf/util/pmus.c
> +++ b/tools/perf/util/pmus.c
> @@ -10,6 +10,7 @@
> #include <pthread.h>
> #include <string.h>
> #include <unistd.h>
> +#include "cpumap.h"
> #include "debug.h"
> #include "evsel.h"
> #include "pmus.h"
> @@ -268,7 +269,7 @@ struct perf_pmu *perf_pmus__scan_core(struct perf_pmu *pmu)
> {
> if (!pmu) {
> pmu_read_sysfs(/*core_only=*/true);
> - pmu = list_prepare_entry(pmu, &core_pmus, list);
> + return list_first_entry_or_null(&core_pmus, typeof(*pmu), list);
> }
> list_for_each_entry_continue(pmu, &core_pmus, list)
> return pmu;
> @@ -592,3 +593,20 @@ struct perf_pmu *evsel__find_pmu(const struct evsel *evsel)
> }
> return pmu;
> }
> +
> +struct perf_pmu *perf_pmus__find_core_pmu(void)
> +{
> + struct perf_pmu *pmu = NULL;
> +
> + while ((pmu = perf_pmus__scan_core(pmu))) {
> + /*
> + * The cpumap should cover all CPUs. Otherwise, some CPUs may
> + * not support some events or have different event IDs.
> + */
> + if (RC_CHK_ACCESS(pmu->cpus)->nr != cpu__max_cpu().cpu)
> + return NULL;
> +
> + return pmu;
> + }
> + return NULL;
> +}
> --
> 2.34.1
>
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