[PATCH v3] perf trace: BTF-based enum pretty printing
Howard Chu
howardchu95 at gmail.com
Thu Jun 13 02:27:57 UTC 2024
changes in v3:
- Fixed another awkward formatting issue in trace__load_vmlinux_btf()
changes in v2:
- Fix formatting issues
- Pass a &use_btf to syscall_arg_fmt__init_array(), instead of
traversing all the arguments again.
- Add a trace__load_vmlinux_btf() function to load vmlinux BTF
- Add member 'btf_entry' in 'struct syscall_arg_fmt' to save the entry to
the corresponding 'struct btf_member' object, without having to do
btf__find_by_name(), btf__type_by_id(), btf_enum(), and btf_vlen()
everytime a syscall enters.
In 'struct syscall_arg_fmt':
```
struct {
void *entry;
u16 nr_entries;
} btf_entry;
```
This is the new member btf_entry. 'struct btf_member' object, so that
we don't have to do btf__find_by_name(), btf__type_by_id(), btf_enum(),
and btf_vlen() everytime a landlock_add_rule() syscall entered.
Note that entry is of type 'void *', because this btf_entry can also be
applied to 'struct btf_member *' for 'BTF_KIND_STRUCT', hopefully in the
future.
===
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
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)
```
Signed-off-by: Howard Chu <howardchu95 at gmail.com>
---
tools/perf/builtin-trace.c | 97 ++++++++++++++++++++++++++++++++++++--
1 file changed, 93 insertions(+), 4 deletions(-)
diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 5cbe1748911d..740285a1f189 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);
@@ -1798,7 +1869,8 @@ 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 +1883,7 @@ 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 +1956,13 @@ 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->btf == NULL)
+ trace__load_vmlinux_btf(trace);
+
+ return err;
}
static int evsel__init_tp_arg_scnprintf(struct evsel *evsel)
@@ -1891,7 +1970,7 @@ 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 +2182,16 @@ 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
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