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Date: Thu, 20 Jun 2024 01:59:37 +0800
From: Howard Chu <howardchu95@...il.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>,
Kan Liang <kan.liang@...ux.intel.com>, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 2/5] perf trace: Augment enum syscall arguments with BTF
Hello,
Thanks for the in-depth review.
On Wed, Jun 19, 2024 at 9:44 PM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> On Wed, Jun 19, 2024 at 04:20:39PM +0800, Howard Chu wrote:
> > This is a feature implemented on the basis of the previous bug fix
> > https://lore.kernel.org/linux-perf-users/d18a9606-ac9f-4ca7-afaf-fcf4c951cb90@web.de/T/#t
> >
> > In this patch, BTF is used to turn enum value to the corresponding
> > enum variable 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 decides to run `perf trace`
> > without any arguments, the behaviour is to trace `landlock_add_rule`,
> > so vmlinux btf will be loaded by default.
> >
> > 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)
> > ```
> > Tested-by: Arnaldo Carvalho de Melo <acme@...nel.org>
> > Suggested-by: Arnaldo Carvalho de Melo <acme@...nel.org>
> > Reviewed-by: Arnaldo Carvalho de Melo <acme@...nel.org>
> > Signed-off-by: Howard Chu <howardchu95@...il.com>
> > ---
> > tools/perf/builtin-trace.c | 96 ++++++++++++++++++++++++++++++++++++--
> > 1 file changed, 91 insertions(+), 5 deletions(-)
> >
> > diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> > index c4fa8191253d..d93f34e9af74 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 +111,11 @@ struct syscall_arg_fmt {
> > const char *name;
> > u16 nr_entries; // for arrays
> > bool show_zero;
> > + bool is_enum;
> > + struct {
> > + void *entries;
> > + u16 nr_entries;
> > + } btf_entry;
> > };
> >
> > struct syscall_fmt {
> > @@ -140,6 +146,7 @@ struct trace {
> > #ifdef HAVE_BPF_SKEL
> > struct augmented_raw_syscalls_bpf *skel;
> > #endif
> > + struct btf *btf;
> > struct record_opts opts;
> > struct evlist *evlist;
> > struct machine *host;
> > @@ -897,6 +904,56 @@ static size_t syscall_arg__scnprintf_getrandom_flags(char *bf, size_t size,
> > .strtoul = STUL_STRARRAY_FLAGS, \
> > .parm = &strarray__##array, }
> >
> > +static int btf_enum_find_entry(struct btf *btf, char *type, struct syscall_arg_fmt *arg_fmt)
> > +{
> > + const struct btf_type *bt;
> > + char enum_prefix[][16] = { "enum", "const enum" }, *ep;
> > + int id;
> > + size_t i;
> > +
> > + for (i = 0; i < ARRAY_SIZE(enum_prefix); i++) {
> > + ep = enum_prefix[i];
> > + if (strlen(type) > strlen(ep) + 1 && strstarts(type, ep))
>
> No need for the strlen test? I.e. plain using strstarts() should be
> enough?
Agree. Thanks for pointing that out. Although if string 'type' is
'enum' and prefix is 'enum', strstarts() will be true, but to do 'type
+= strlen(ep) + 1', and then access 'type', might give us an
out-of-range access, but I don't think 'type' will ever be just 'enum'
or 'const enum', so I'll delete it then.
>
> > + type += strlen(ep) + 1;
> > + }
> > +
> > + id = btf__find_by_name(btf, type);
> > + if (id < 0)
> > + return -1;
> > +
> > + bt = btf__type_by_id(btf, id);
> > + if (bt == NULL)
>
> a pr_debug() stating that something that tracefs says should be in BTF
> and isn't found there seems to be of value here.
Sure.
>
> > + return -1;
> > +
> > + arg_fmt->btf_entry.entries = btf_enum(bt);
> > + arg_fmt->btf_entry.nr_entries = btf_vlen(bt);
> > +
> > + return 0;
> > +}
> > +
> > +static size_t btf_enum_scnprintf(char *bf, size_t size, int val, struct btf *btf, char *type,
> > + struct syscall_arg_fmt *arg_fmt)
> > +{
> > + struct btf_enum *be;
> > + int i;
> > +
> > + /* if btf_entry is NULL, find and save it to arg_fmt */
> > + if (arg_fmt->btf_entry.entries == NULL)
> > + if (btf_enum_find_entry(btf, type, arg_fmt))
> > + return 0;
> > +
> > + be = (struct btf_enum *)arg_fmt->btf_entry.entries;
>
> struct btf_enum *be = (struct btf_enum *)arg_fmt->btf_entry.entries;
>
> arg_fmt->btf_entry.entries is (void *), so we don't need the (struct
> btf_enum *) cast here, removing it makes the code more compact. And
> since we move the declaration to the same line, the info about its type
> is there as well.
Sure, thanks.
>
> > +
> > + for (i = 0; i < arg_fmt->btf_entry.nr_entries; ++i, ++be) {
>
>
> for (int i = 0; i < arg_fmt->btf_entry.nr_entries; ++i, ++be) {
>
> ⬢[acme@...lbox perf-tools-next]$ git grep 'for (int ' tools/perf/ | wc -l
> 99
> ⬢[acme@...lbox perf-tools-next]$
>
> Doing it this way makes the code more compact and is allowed even in
> kernel code since some time ago:
Sure.
>
> ⬢[acme@...lbox perf-tools-next]$ git grep 'for (int ' drivers/ | wc -l
> 294
> ⬢[acme@...lbox perf-tools-next]$ git grep 'for (int ' kernel/ | wc -l
> 12
> ⬢[acme@...lbox perf-tools-next]$ git grep 'for (int ' net/ | wc -l
> 3
> ⬢[acme@...lbox perf-tools-next]$ git grep 'for (int ' mm/ | wc -l
> 21
> ⬢[acme@...lbox perf-tools-next]$
>
> > + if (be->val == val) {
> > + return scnprintf(bf, size, "%s",
> > + btf__name_by_offset(btf, be->name_off));
> > + }
> > + }
> > +
> > + return 0;
> > +}
> > +
> > #include "trace/beauty/arch_errno_names.c"
> > #include "trace/beauty/eventfd.c"
> > #include "trace/beauty/futex_op.c"
> > @@ -1699,6 +1756,15 @@ static void trace__symbols__exit(struct trace *trace)
> > symbol__exit();
> > }
> >
> > +static void trace__load_vmlinux_btf(struct trace *trace)
> > +{
> > + trace->btf = btf__load_vmlinux_btf();
> > + if (verbose > 0) {
> > + fprintf(trace->output, trace->btf ? "vmlinux BTF loaded\n" :
> > + "Failed to load vmlinux BTF\n");
> > + }
> > +}
> > +
> > static int syscall__alloc_arg_fmts(struct syscall *sc, int nr_args)
> > {
> > int idx;
> > @@ -1744,7 +1810,7 @@ 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;
> > @@ -1782,6 +1848,8 @@ 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;
>
> Here you have to check if use_btf is NULL, as you, in this patch, later
> call syscall_arg_fmt__init_array(arg, field, NULL) in
> evsel__init_tp_arg_scnprintf(), probably you tested it all at the end of
> the patch series, we have to make sure that it works after each patch,
> so that we keep the codebase bisectable.
I'm sorry, could you enlighten me on this? I thought:
```
else if (strstr(field->type, "enum") && use_btf != NULL) {
```
is doing the NULL checking. If you mean making sure the NULL checking
appears in all patches, I thought this is where we should introduce
the checking. Tiny reminder, the [1/5] patch is your syscalltbl
traversal bug fix.
>
> > } else {
> > const struct syscall_arg_fmt *fmt =
> > syscall_arg_fmt__find_by_name(field->name);
> > @@ -1796,9 +1864,10 @@ syscall_arg_fmt__init_array(struct syscall_arg_fmt *arg, struct tep_format_field
> > return last_field;
> > }
> >
> > -static int syscall__set_arg_fmts(struct syscall *sc)
> > +static int syscall__set_arg_fmts(struct syscall *sc, bool *use_btf)
> > {
> > - 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,
> > + use_btf);
> >
> > if (last_field)
> > sc->args_size = last_field->offset + last_field->size;
> > @@ -1810,7 +1879,9 @@ static int trace__read_syscall_info(struct trace *trace, int id)
> > {
> > char tp_name[128];
> > struct syscall *sc;
> > + int err;
> > const char *name = syscalltbl__name(trace->sctbl, id);
> > + bool use_btf = false;
> >
> > #ifdef HAVE_SYSCALL_TABLE_SUPPORT
> > if (trace->syscalls.table == NULL) {
> > @@ -1883,7 +1954,12 @@ 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, &use_btf);
> > +
> > + if (use_btf && trace->btf == NULL)
> > + trace__load_vmlinux_btf(trace);
> > +
> > + return err;
> > }
> >
> > static int evsel__init_tp_arg_scnprintf(struct evsel *evsel)
> > @@ -1891,7 +1967,7 @@ 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 +2179,16 @@ 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 && trace->btf) {
> > + size_t p = btf_enum_scnprintf(bf + printed, size - printed, val,
> > + trace->btf, field->type,
> > + &sc->arg_fmt[arg.idx]);
> > + 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
> >
Thanks,
Howard
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