perf tools: Synthesize bpf_trampoline/dispatcher ksymbol event

Synthesize bpf images (trampolines/dispatchers) on start, as ksymbol
events from /proc/kallsyms. Having this perf can recognize samples from
those images and perf report and top shows them correctly.

The rest of the ksymbol handling is already in place from for the bpf
programs monitoring, so only the initial state was needed.

perf report output:

  # Overhead  Command     Shared Object                  Symbol

    12.37%  test_progs  [kernel.vmlinux]                 [k] entry_SYSCALL_64
    11.80%  test_progs  [kernel.vmlinux]                 [k] syscall_return_via_sysret
     9.63%  test_progs  bpf_prog_bcf7977d3b93787c_prog2  [k] bpf_prog_bcf7977d3b93787c_prog2
     6.90%  test_progs  bpf_trampoline_24456             [k] bpf_trampoline_24456
     6.36%  test_progs  [kernel.vmlinux]                 [k] memcpy_erms

Committer notes:

Use scnprintf() instead of strncpy() to overcome this on fedora:32,
rawhide and OpenMandriva Cooker:

    CC       /tmp/build/perf/util/bpf-event.o
  In file included from /usr/include/string.h:495,
                   from /git/linux/tools/lib/bpf/libbpf_common.h:12,
                   from /git/linux/tools/lib/bpf/bpf.h:31,
                   from util/bpf-event.c:4:
  In function 'strncpy',
      inlined from 'process_bpf_image' at util/bpf-event.c:323:2,
      inlined from 'kallsyms_process_symbol' at util/bpf-event.c:358:9:
  /usr/include/bits/string_fortified.h:106:10: error: '__builtin_strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
    106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos (__dest));
        |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

Signed-off-by: Jiri Olsa <[email protected]>
Acked-by: Song Liu <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Björn Töpel <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Jesper Dangaard Brouer <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Yonghong Song <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]/
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

1 files changed, 93 insertions, 0 deletions

diff --git a/tools/perf/util/bpf-event.c b/tools/perf/util/bpf-event.c
index a3207d900339..0cd41a862952 100644
--- a/tools/perf/util/bpf-event.c
+++ b/tools/perf/util/bpf-event.c
@@ -6,6 +6,9 @@
 #include <bpf/libbpf.h>
 #include <linux/btf.h>
 #include <linux/err.h>
+#include <linux/string.h>
+#include <internal/lib.h>
+#include <symbol/kallsyms.h>
 #include "bpf-event.h"
 #include "debug.h"
 #include "dso.h"
@@ -290,11 +293,82 @@ out:
 	return err ? -1 : 0;
 }
 
+struct kallsyms_parse {
+	union perf_event	*event;
+	perf_event__handler_t	 process;
+	struct machine		*machine;
+	struct perf_tool	*tool;
+};
+
+static int
+process_bpf_image(char *name, u64 addr, struct kallsyms_parse *data)
+{
+	struct machine *machine = data->machine;
+	union perf_event *event = data->event;
+	struct perf_record_ksymbol *ksymbol;
+	int len;
+
+	ksymbol = &event->ksymbol;
+
+	*ksymbol = (struct perf_record_ksymbol) {
+		.header = {
+			.type = PERF_RECORD_KSYMBOL,
+			.size = offsetof(struct perf_record_ksymbol, name),
+		},
+		.addr      = addr,
+		.len       = page_size,
+		.ksym_type = PERF_RECORD_KSYMBOL_TYPE_BPF,
+		.flags     = 0,
+	};
+
+	len = scnprintf(ksymbol->name, KSYM_NAME_LEN, "%s", name);
+	ksymbol->header.size += PERF_ALIGN(len + 1, sizeof(u64));
+	memset((void *) event + event->header.size, 0, machine->id_hdr_size);
+	event->header.size += machine->id_hdr_size;
+
+	return perf_tool__process_synth_event(data->tool, event, machine,
+					      data->process);
+}
+
+static int
+kallsyms_process_symbol(void *data, const char *_name,
+			char type __maybe_unused, u64 start)
+{
+	char disp[KSYM_NAME_LEN];
+	char *module, *name;
+	unsigned long id;
+	int err = 0;
+
+	module = strchr(_name, '\t');
+	if (!module)
+		return 0;
+
+	/* We are going after [bpf] module ... */
+	if (strcmp(module + 1, "[bpf]"))
+		return 0;
+
+	name = memdup(_name, (module - _name) + 1);
+	if (!name)
+		return -ENOMEM;
+
+	name[module - _name] = 0;
+
+	/* .. and only for trampolines and dispatchers */
+	if ((sscanf(name, "bpf_trampoline_%lu", &id) == 1) ||
+	    (sscanf(name, "bpf_dispatcher_%s", disp) == 1))
+		err = process_bpf_image(name, start, data);
+
+	free(name);
+	return err;
+}
+
 int perf_event__synthesize_bpf_events(struct perf_session *session,
 				      perf_event__handler_t process,
 				      struct machine *machine,
 				      struct record_opts *opts)
 {
+	const char *kallsyms_filename = "/proc/kallsyms";
+	struct kallsyms_parse arg;
 	union perf_event *event;
 	__u32 id = 0;
 	int err;
@@ -303,6 +377,8 @@ int perf_event__synthesize_bpf_events(struct perf_session *session,
 	event = malloc(sizeof(event->bpf) + KSYM_NAME_LEN + machine->id_hdr_size);
 	if (!event)
 		return -1;
+
+	/* Synthesize all the bpf programs in system. */
 	while (true) {
 		err = bpf_prog_get_next_id(id, &id);
 		if (err) {
@@ -335,6 +411,23 @@ int perf_event__synthesize_bpf_events(struct perf_session *session,
 			break;
 		}
 	}
+
+	/* Synthesize all the bpf images - trampolines/dispatchers. */
+	if (symbol_conf.kallsyms_name != NULL)
+		kallsyms_filename = symbol_conf.kallsyms_name;
+
+	arg = (struct kallsyms_parse) {
+		.event   = event,
+		.process = process,
+		.machine = machine,
+		.tool    = session->tool,
+	};
+
+	if (kallsyms__parse(kallsyms_filename, &arg, kallsyms_process_symbol)) {
+		pr_err("%s: failed to synthesize bpf images: %s\n",
+		       __func__, strerror(errno));
+	}
+
 	free(event);
 	return err;
 }