Re: [PATCH v4] perf trace: BTF-based enum pretty printing

From: Arnaldo Carvalho de Melo
Date: Thu Jun 13 2024 - 08:47:36 EST

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In reply to: Howard Chu: "[PATCH v4] perf trace: BTF-based enum pretty printing"
Next in thread: Arnaldo Carvalho de Melo: "Re: [PATCH v4] perf trace: BTF-based enum pretty printing"
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On Thu, Jun 13, 2024 at 12:27:47PM +0800, Howard Chu wrote:
> changes in v4:
>
> - Add enum support to tracepoint arguments

That is cool, but see below the comment as having this as a separate
patch.

Also please, on the patch that introduces ! syscall tracepoint enum args
BTF augmentation include examples of tracepoints being augmented. I'll
try here while testing the patch as-is.

More comments below.

> - For tracing syscalls, move trace__load_vmlinux_btf() to
> syscall__set_arg_fmts() to make it more elegant
>
> changes in v3:
>
> - Fixed another awkward formatting issue in trace__load_vmlinux_btf()
>
> changes in v2:
>
> - Fix formatting issues

<SNIP>

> 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)
> ```
>
> Signed-off-by: Howard Chu <howardchu95@xxxxxxxxx>
> ---
> tools/perf/builtin-trace.c | 121 ++++++++++++++++++++++++++++++++++---
> 1 file changed, 111 insertions(+), 10 deletions(-)
>
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 5cbe1748911d..0a168cb9b0c2 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 *entry;
> + 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;
> @@ -887,6 +894,56 @@ static size_t syscall_arg__scnprintf_getrandom_flags(char *bf, size_t size,
>
> #define SCA_GETRANDOM_FLAGS syscall_arg__scnprintf_getrandom_flags
>
> +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))
> + 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)
> + return -1;
> +
> + arg_fmt->btf_entry.entry = 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.entry == NULL)
> + if (btf_enum_find_entry(btf, type, arg_fmt))
> + return 0;
> +
> + be = (struct btf_enum *)arg_fmt->btf_entry.entry;
> +
> + for (i = 0; i < arg_fmt->btf_entry.nr_entries; ++i, ++be) {
> + if (be->val == val) {
> + return scnprintf(bf, size, "%s",
> + btf__name_by_offset(btf, be->name_off));
> + }
> + }
> +
> + return 0;
> +}
> +
> #define STRARRAY(name, array) \
> { .scnprintf = SCA_STRARRAY, \
> .strtoul = STUL_STRARRAY, \
> @@ -1238,6 +1295,7 @@ 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;
> @@ -1699,6 +1757,15 @@ 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 +1811,8 @@ 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 +1824,7 @@ 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 +1851,8 @@ 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);
> @@ -1796,9 +1867,14 @@ 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 trace *trace, struct syscall *sc)

See the comment about evsel__init_tp_arg_scnprintf() below. Also please
do patches on top of previous work, i.e. the v3 patch should be a
separate patch and this v4 should add the extra functionality, i.e. the
support for !syscall tracepoint enum BTF augmentation.

> {
> - struct tep_format_field *last_field = syscall_arg_fmt__init_array(sc->arg_fmt, sc->args);
> + bool use_btf;
> + struct tep_format_field *last_field = syscall_arg_fmt__init_array(sc->arg_fmt, sc->args,
> + &use_btf);
> +
> + if (use_btf && trace->btf == NULL)
> + trace__load_vmlinux_btf(trace);
>
> if (last_field)
> sc->args_size = last_field->offset + last_field->size;
> @@ -1883,15 +1959,20 @@ 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);
> + return syscall__set_arg_fmts(trace, sc);
> }
>
> -static int evsel__init_tp_arg_scnprintf(struct evsel *evsel)
> +static int evsel__init_tp_arg_scnprintf(struct trace *trace, struct evsel *evsel)

The convention here is that evsel__ is the "class" name, so the first
arg is a 'struct evsel *', if you really were transforming this into a
'struct trace' specific "method" you would change the name of the C
function to 'trace__init_tp_arg_scnprintf'.

But in this case instead of passing the 'struct trace' pointer all the
way down we should instead pass a 'bool *use_btf' argument, making it:

static int evsel__init_tp_arg_scnprintf(struct evsel *evsel, bool *use_btf)

Then, when evlist__set_syscall_tp_fields(evlist, &use_btf) returns,
check that use_btf to check if we need to call
trace__load_vmlinux_btf(trace).

I'll test the patch as is now.

- Arnaldo

> {
> struct syscall_arg_fmt *fmt = evsel__syscall_arg_fmt(evsel);
> + bool use_btf;
>
> 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, &use_btf);
> +
> + if (use_btf && trace->btf == NULL)
> + trace__load_vmlinux_btf(trace);
> +
> return 0;
> }
>
> @@ -2103,6 +2184,16 @@ 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);
> }
> @@ -2791,7 +2882,7 @@ static size_t trace__fprintf_tp_fields(struct trace *trace, struct evsel *evsel,
> val = syscall_arg_fmt__mask_val(arg, &syscall_arg, val);
>
> /* Suppress this argument if its value is zero and show_zero property isn't set. */
> - if (val == 0 && !trace->show_zeros && !arg->show_zero)
> + if (val == 0 && !trace->show_zeros && !arg->show_zero && !arg->is_enum)
> continue;
>
> printed += scnprintf(bf + printed, size - printed, "%s", printed ? ", " : "");
> @@ -2799,6 +2890,15 @@ static size_t trace__fprintf_tp_fields(struct trace *trace, struct evsel *evsel,
> if (trace->show_arg_names)
> printed += scnprintf(bf + printed, size - printed, "%s: ", field->name);
>
> + if (arg->is_enum && trace->btf) {
> + size_t p = btf_enum_scnprintf(bf + printed, size - printed, val, trace->btf,
> + field->type, arg);
> + if (p) {
> + printed += p;
> + continue;
> + }
> + }
> +
> printed += syscall_arg_fmt__scnprintf_val(arg, bf + printed, size - printed, &syscall_arg, val);
> }
>
> @@ -4461,8 +4561,9 @@ static void evsel__set_syscall_arg_fmt(struct evsel *evsel, const char *name)
> }
> }
>
> -static int evlist__set_syscall_tp_fields(struct evlist *evlist)
> +static int evlist__set_syscall_tp_fields(struct trace *trace)
> {
> + struct evlist *evlist = trace->evlist;
> struct evsel *evsel;
>
> evlist__for_each_entry(evlist, evsel) {
> @@ -4470,7 +4571,7 @@ static int evlist__set_syscall_tp_fields(struct evlist *evlist)
> continue;
>
> if (strcmp(evsel->tp_format->system, "syscalls")) {
> - evsel__init_tp_arg_scnprintf(evsel);
> + evsel__init_tp_arg_scnprintf(trace, evsel);
> continue;
> }
>
> @@ -4949,7 +5050,7 @@ int cmd_trace(int argc, const char **argv)
>
> if (trace.evlist->core.nr_entries > 0) {
> evlist__set_default_evsel_handler(trace.evlist, trace__event_handler);
> - if (evlist__set_syscall_tp_fields(trace.evlist)) {
> + if (evlist__set_syscall_tp_fields(&trace)) {
> perror("failed to set syscalls:* tracepoint fields");
> goto out;
> }
> --
> 2.45.2
>

Next message: Greg Kroah-Hartman: "[PATCH 6.1 00/85] 6.1.94-rc1 review"
Previous message: Paul E. McKenney: "Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache_free callback"
In reply to: Howard Chu: "[PATCH v4] perf trace: BTF-based enum pretty printing"
Next in thread: Arnaldo Carvalho de Melo: "Re: [PATCH v4] perf trace: BTF-based enum pretty printing"
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