Message-ID: <CAH0uvohFMtQ+Cg_2PFnW=-pHkSsp-ciqFO6YO-nYJ91Dd1Aa8Q@mail.gmail.com>
Date: Thu, 11 Jul 2024 23:16:09 +0800
From: Howard Chu <howardchu95@...il.com>
To: Ian Rogers <irogers@...gle.com>
Cc: acme@...nel.org, adrian.hunter@...el.com, jolsa@...nel.org, 
	kan.liang@...ux.intel.com, namhyung@...nel.org, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Arnaldo Carvalho de Melo <acme@...hat.com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Günther Noack <gnoack@...gle.com>, 
	Ingo Molnar <mingo@...hat.com>, Mark Rutland <mark.rutland@....com>, 
	Mickaël Salaün <mic@...ikod.net>, 
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v5 2/8] perf trace: BTF-based enum pretty printing for
 syscall args

Hello,

Thank you for the advice! Although I am not the person who wrote this
comment, I think it's good to change it to /* */ instead.

Thanks,
Howard

On Thu, Jul 11, 2024 at 1:54 AM Ian Rogers <irogers@...gle.com> wrote:
>
> On Fri, Jul 5, 2024 at 2:43 AM Howard Chu <howardchu95@...il.com> wrote:
> >
> > In this patch, BTF is used to turn enum value to the corresponding
> > name. There is only one system call that uses enum value as its
> > argument, that is `landlock_add_rule()`.
> >
> > The vmlinux btf is loaded lazily, when user decided to trace the
> > `landlock_add_rule` syscall. But if one decide to run `perf trace`
> > without any arguments, the behaviour is to trace `landlock_add_rule`,
> > so vmlinux btf will be loaded by default.
> >
> > The laziest behaviour is to load vmlinux btf when a
> > `landlock_add_rule` syscall hits. But I think you could lose some
> > samples when loading vmlinux btf at run time, for it can delay the
> > handling of other samples. I might need your precious opinions on
> > this...
> >
> > before:
> >
> > ```
> > perf $ ./perf trace -e landlock_add_rule
> >      0.000 ( 0.008 ms): ldlck-test/438194 landlock_add_rule(rule_type: 2) = -1 EBADFD (File descriptor in bad state)
> >      0.010 ( 0.001 ms): ldlck-test/438194 landlock_add_rule(rule_type: 1) = -1 EBADFD (File descriptor in bad state)
> > ```
> >
> > after:
> >
> > ```
> > perf $ ./perf trace -e landlock_add_rule
> >      0.000 ( 0.029 ms): ldlck-test/438194 landlock_add_rule(rule_type: LANDLOCK_RULE_NET_PORT)     = -1 EBADFD (File descriptor in bad state)
> >      0.036 ( 0.004 ms): ldlck-test/438194 landlock_add_rule(rule_type: LANDLOCK_RULE_PATH_BENEATH) = -1 EBADFD (File descriptor in bad state)
> > ```
> >
> > Committer notes:
> >
> > Made it build with NO_LIBBPF=1, simplified btf_enum_fprintf(), see [1]
> > for the discussion.
> >
> > Signed-off-by: Howard Chu <howardchu95@...il.com>
> > Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> > Cc: Adrian Hunter <adrian.hunter@...el.com>
> > Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > Cc: Günther Noack <gnoack@...gle.com>
> > Cc: Ian Rogers <irogers@...gle.com>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > Cc: Kan Liang <kan.liang@...ux.intel.com>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Mickaël Salaün <mic@...ikod.net>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Link: https://lore.kernel.org/lkml/20240613022757.3589783-1-howardchu95@gmail.com
> > Link: https://lore.kernel.org/lkml/ZnXAhFflUl_LV1QY@x1 # [1]
> > Link: https://lore.kernel.org/r/20240624181345.124764-3-howardchu95@gmail.com
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> > ---
> >  tools/perf/builtin-trace.c | 110 +++++++++++++++++++++++++++++++++++--
> >  1 file changed, 106 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> > index 8449f2beb54d..1391564911d9 100644
> > --- a/tools/perf/builtin-trace.c
> > +++ b/tools/perf/builtin-trace.c
> > @@ -19,6 +19,7 @@
> >  #ifdef HAVE_LIBBPF_SUPPORT
> >  #include <bpf/bpf.h>
> >  #include <bpf/libbpf.h>
> > +#include <bpf/btf.h>
> >  #ifdef HAVE_BPF_SKEL
> >  #include "bpf_skel/augmented_raw_syscalls.skel.h"
> >  #endif
> > @@ -110,6 +111,10 @@ struct syscall_arg_fmt {
> >         const char *name;
> >         u16        nr_entries; // for arrays
> >         bool       show_zero;
> > +       bool       is_enum;
> > +#ifdef HAVE_LIBBPF_SUPPORT
> > +       const struct btf_type *type;
> > +#endif
> >  };
> >
> >  struct syscall_fmt {
> > @@ -139,6 +144,9 @@ struct trace {
> >         } syscalls;
> >  #ifdef HAVE_BPF_SKEL
> >         struct augmented_raw_syscalls_bpf *skel;
> > +#endif
> > +#ifdef HAVE_LIBBPF_SUPPORT
> > +       struct btf              *btf;
> >  #endif
> >         struct record_opts      opts;
> >         struct evlist   *evlist;
> > @@ -204,6 +212,20 @@ struct trace {
> >         } oe;
> >  };
> >
> > +static void trace__load_vmlinux_btf(struct trace *trace __maybe_unused)
> > +{
> > +#ifdef HAVE_LIBBPF_SUPPORT
> > +       if (trace->btf != NULL)
> > +               return;
> > +
> > +       trace->btf = btf__load_vmlinux_btf();
> > +       if (verbose > 0) {
> > +               fprintf(trace->output, trace->btf ? "vmlinux BTF loaded\n" :
> > +                                                   "Failed to load vmlinux BTF\n");
> > +       }
> > +#endif
> > +}
> > +
> >  struct tp_field {
> >         int offset;
> >         union {
> > @@ -887,6 +909,64 @@ static size_t syscall_arg__scnprintf_getrandom_flags(char *bf, size_t size,
> >
> >  #define SCA_GETRANDOM_FLAGS syscall_arg__scnprintf_getrandom_flags
> >
> > +#ifdef HAVE_LIBBPF_SUPPORT
> > +static int syscall_arg_fmt__cache_btf_enum(struct syscall_arg_fmt *arg_fmt, struct btf *btf, char *type)
> > +{
> > +       int id;
> > +
> > +       // Already cached?
>
> Hi Howard,
>
> I'm on nit patrol again, just to note that most comments are /* */
> style although we do have // comments - the ratio of /* */ to // is
> about 10:1. The kernel is similar in this regard. There's no clear
> guidance so we could ignore this, but fwiw I generally try to stick
> with /* */ for consistency with the rest of the surrounding code.
>
> Thanks,
> Ian
> > +       if (arg_fmt->type != NULL)
> > +               return 0;
> > +
> > +       type = strstr(type, "enum ");
> > +       if (type == NULL)
> > +               return -1;
> > +
> > +       type += 5; // skip "enum " to get the enumeration name
> > +
> > +       id = btf__find_by_name(btf, type);
> > +       if (id < 0)
> > +               return -1;
> > +
> > +       arg_fmt->type = btf__type_by_id(btf, id);
> > +       return arg_fmt->type == NULL ? -1 : 0;
> > +}
> > +
> > +static size_t btf_enum_scnprintf(const struct btf_type *type, struct btf *btf, char *bf, size_t size, int val)
> > +{
> > +       struct btf_enum *be = btf_enum(type);
> > +       const int nr_entries = btf_vlen(type);
> > +
> > +       for (int i = 0; i < nr_entries; ++i, ++be) {
> > +               if (be->val == val) {
> > +                       return scnprintf(bf, size, "%s",
> > +                                        btf__name_by_offset(btf, be->name_off));
> > +               }
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static size_t trace__btf_enum_scnprintf(struct trace *trace, struct syscall_arg_fmt *arg_fmt, char *bf,
> > +                                       size_t size, int val, char *type)
> > +{
> > +       if (trace->btf == NULL)
> > +               return 0;
> > +
> > +       if (syscall_arg_fmt__cache_btf_enum(arg_fmt, trace->btf, type) < 0)
> > +               return 0;
> > +
> > +       return btf_enum_scnprintf(arg_fmt->type, trace->btf, bf, size, val);
> > +}
> > +#else // HAVE_LIBBPF_SUPPORT
> > +static size_t trace__btf_enum_scnprintf(struct trace *trace __maybe_unused, struct syscall_arg_fmt *arg_fmt __maybe_unused,
> > +                                       char *bf __maybe_unused, size_t size __maybe_unused, int val __maybe_unused,
> > +                                       char *type __maybe_unused)
> > +{
> > +       return 0;
> > +}
> > +#endif // HAVE_LIBBPF_SUPPORT
> > +
> >  #define STRARRAY(name, array) \
> >           { .scnprintf  = SCA_STRARRAY, \
> >             .strtoul    = STUL_STRARRAY, \
> > @@ -1238,6 +1318,7 @@ struct syscall {
> >         bool                is_exit;
> >         bool                is_open;
> >         bool                nonexistent;
> > +       bool                use_btf;
> >         struct tep_format_field *args;
> >         const char          *name;
> >         const struct syscall_fmt  *fmt;
> > @@ -1744,7 +1825,8 @@ static const struct syscall_arg_fmt *syscall_arg_fmt__find_by_name(const char *n
> >  }
> >
> >  static struct tep_format_field *
> > -syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field *field)
> > +syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field *field,
> > +                           bool *use_btf)
> >  {
> >         struct tep_format_field *last_field = NULL;
> >         int len;
> > @@ -1756,6 +1838,7 @@ syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field
> >                         continue;
> >
> >                 len = strlen(field->name);
> > +               arg->is_enum = false;
> >
> >                 if (strcmp(field->type, "const char *") == 0 &&
> >                     ((len >= 4 && strcmp(field->name + len - 4, "name") == 0) ||
> > @@ -1782,6 +1865,8 @@ syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field
> >                          * 7 unsigned long
> >                          */
> >                         arg->scnprintf = SCA_FD;
> > +               } else if (strstr(field->type, "enum") && use_btf != NULL) {
> > +                       *use_btf = arg->is_enum = true;
> >                 } else {
> >                         const struct syscall_arg_fmt *fmt =
> >                                 syscall_arg_fmt__find_by_name(field->name);
> > @@ -1798,7 +1883,8 @@ syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field
> >
> >  static int syscall__set_arg_fmts(struct syscall *sc)
> >  {
> > -       struct tep_format_field *last_field = syscall_arg_fmt__init_array(sc->arg_fmt, sc->args);
> > +       struct tep_format_field *last_field = syscall_arg_fmt__init_array(sc->arg_fmt, sc->args,
> > +                                                                         &sc->use_btf);
> >
> >         if (last_field)
> >                 sc->args_size = last_field->offset + last_field->size;
> > @@ -1811,6 +1897,7 @@ static int trace__read_syscall_info(struct trace *trace, int id)
> >         char tp_name[128];
> >         struct syscall *sc;
> >         const char *name = syscalltbl__name(trace->sctbl, id);
> > +       int err;
> >
> >  #ifdef HAVE_SYSCALL_TABLE_SUPPORT
> >         if (trace->syscalls.table == NULL) {
> > @@ -1883,7 +1970,13 @@ static int trace__read_syscall_info(struct trace *trace, int id)
> >         sc->is_exit = !strcmp(name, "exit_group") || !strcmp(name, "exit");
> >         sc->is_open = !strcmp(name, "open") || !strcmp(name, "openat");
> >
> > -       return syscall__set_arg_fmts(sc);
> > +       err = syscall__set_arg_fmts(sc);
> > +
> > +       /* after calling syscall__set_arg_fmts() we'll know whether use_btf is true */
> > +       if (sc->use_btf)
> > +               trace__load_vmlinux_btf(trace);
> > +
> > +       return err;
> >  }
> >
> >  static int evsel__init_tp_arg_scnprintf(struct evsel *evsel)
> > @@ -1891,7 +1984,7 @@ static int evsel__init_tp_arg_scnprintf(struct evsel *evsel)
> >         struct syscall_arg_fmt *fmt = evsel__syscall_arg_fmt(evsel);
> >
> >         if (fmt != NULL) {
> > -               syscall_arg_fmt__init_array(fmt, evsel->tp_format->format.fields);
> > +               syscall_arg_fmt__init_array(fmt, evsel->tp_format->format.fields, NULL);
> >                 return 0;
> >         }
> >
> > @@ -2103,6 +2196,15 @@ static size_t syscall__scnprintf_args(struct syscall *sc, char *bf, size_t size,
> >                         if (trace->show_arg_names)
> >                                 printed += scnprintf(bf + printed, size - printed, "%s: ", field->name);
> >
> > +                       if (sc->arg_fmt[arg.idx].is_enum) {
> > +                               size_t p = trace__btf_enum_scnprintf(trace, &sc->arg_fmt[arg.idx], bf + printed,
> > +                                                                    size - printed, val, field->type);
> > +                               if (p) {
> > +                                       printed += p;
> > +                                       continue;
> > +                               }
> > +                       }
> > +
> >                         printed += syscall_arg_fmt__scnprintf_val(&sc->arg_fmt[arg.idx],
> >                                                                   bf + printed, size - printed, &arg, val);
> >                 }
> > --
> > 2.45.2
> >

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