[PATCH 009/107] perf trace: Put the per-syscall entry/exit prog_array BPF map infrastructure in place

Arnaldo Carvalho de Melo
2019-07-30T02:56:51Z

From: Arnaldo Carvalho de Melo <acme@redhat.com>

I.e. look for "syscalls_sys_enter" and "syscalls_sys_exit" BPF maps of
type PROG_ARRAY and populate it with the handlers as specified per
syscall, for now only 'open' is wiring it to something, in time all
syscalls that need to copy arguments entering a syscall or returning
from one will set these to the right handlers, reusing when possible
pre-existing ones.

Next step is to use bpf_tail_call() into that.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-t0p4u43i9vbpzs1xtowna3gb@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/builtin-trace.c | 76 ++++++++++++++++++-
.../examples/bpf/augmented_raw_syscalls.c | 14 ++++
2 files changed, 86 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 6cc696edf24a..fb8b8e78d7b5 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -1,4 +1,3 @@
-// SPDX-License-Identifier: GPL-2.0-only
/*
* builtin-trace.c
*
@@ -83,6 +82,10 @@ struct trace {
int max;
struct syscall *table;
struct bpf_map *map;
+ struct { // per syscall BPF_MAP_TYPE_PROG_ARRAY
+ struct bpf_map *sys_enter,
+ *sys_exit;
+ } prog_array;
struct {
struct perf_evsel *sys_enter,
*sys_exit,
@@ -1619,6 +1622,22 @@ static int trace__validate_ev_qualifier(struct trace *trace)
goto out;
}

+static __maybe_unused bool trace__syscall_enabled(struct trace *trace, int id)
+{
+ bool in_ev_qualifier;
+
+ if (trace->ev_qualifier_ids.nr == 0)
+ return true;
+
+ in_ev_qualifier = bsearch(&id, trace->ev_qualifier_ids.entries,
+ trace->ev_qualifier_ids.nr, sizeof(int), intcmp) != NULL;
+
+ if (in_ev_qualifier)
+ return !trace->not_ev_qualifier;
+
+ return trace->not_ev_qualifier;
+}
+
/*
* args is to be interpreted as a series of longs but we need to handle
* 8-byte unaligned accesses. args points to raw_data within the event
@@ -2784,6 +2803,18 @@ static void trace__init_syscall_bpf_progs(struct trace *trace, int id)
}
}

+static int trace__bpf_prog_sys_enter_fd(struct trace *trace, int id)
+{
+ struct syscall *sc = trace__syscall_info(trace, NULL, id);
+ return sc ? bpf_program__fd(sc->bpf_prog.sys_enter) : bpf_program__fd(trace->syscalls.unaugmented_prog);
+}
+
+static int trace__bpf_prog_sys_exit_fd(struct trace *trace, int id)
+{
+ struct syscall *sc = trace__syscall_info(trace, NULL, id);
+ return sc ? bpf_program__fd(sc->bpf_prog.sys_exit) : bpf_program__fd(trace->syscalls.unaugmented_prog);
+}
+
static void trace__init_bpf_map_syscall_args(struct trace *trace, int id, struct bpf_map_syscall_entry *entry)
{
struct syscall *sc = trace__syscall_info(trace, NULL, id);
@@ -2837,10 +2868,8 @@ static int __trace__init_syscalls_bpf_map(struct trace *trace, bool enabled)
int err = 0, key;

for (key = 0; key < trace->sctbl->syscalls.nr_entries; ++key) {
- if (enabled) {
+ if (enabled)
trace__init_bpf_map_syscall_args(trace, key, &value);
- trace__init_syscall_bpf_progs(trace, key);
- }

err = bpf_map_update_elem(fd, &key, &value, BPF_ANY);
if (err)
@@ -2859,6 +2888,34 @@ static int trace__init_syscalls_bpf_map(struct trace *trace)

return __trace__init_syscalls_bpf_map(trace, enabled);
}
+
+static int trace__init_syscalls_bpf_prog_array_maps(struct trace *trace)
+{
+ int map_enter_fd = bpf_map__fd(trace->syscalls.prog_array.sys_enter),
+ map_exit_fd = bpf_map__fd(trace->syscalls.prog_array.sys_exit);
+ int err = 0, key;
+
+ for (key = 0; key < trace->sctbl->syscalls.nr_entries; ++key) {
+ int prog_fd;
+
+ if (!trace__syscall_enabled(trace, key))
+ continue;
+
+ trace__init_syscall_bpf_progs(trace, key);
+
+ // It'll get at least the "!raw_syscalls:unaugmented"
+ prog_fd = trace__bpf_prog_sys_enter_fd(trace, key);
+ err = bpf_map_update_elem(map_enter_fd, &key, &prog_fd, BPF_ANY);
+ if (err)
+ break;
+ prog_fd = trace__bpf_prog_sys_exit_fd(trace, key);
+ err = bpf_map_update_elem(map_exit_fd, &key, &prog_fd, BPF_ANY);
+ if (err)
+ break;
+ }
+
+ return err;
+}
#else
static int trace__set_ev_qualifier_bpf_filter(struct trace *trace __maybe_unused)
{
@@ -2875,6 +2932,11 @@ static struct bpf_program *trace__find_bpf_program_by_title(struct trace *trace
{
return NULL;
}
+
+static int trace__init_syscalls_bpf_prog_array_maps(struct trace *trace __maybe_unused)
+{
+ return 0;
+}
#endif // HAVE_LIBBPF_SUPPORT

static int trace__set_ev_qualifier_filter(struct trace *trace)
@@ -3129,6 +3191,10 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
if (trace->syscalls.map)
trace__init_syscalls_bpf_map(trace);

+ if (trace->syscalls.prog_array.sys_enter)
+ trace__init_syscalls_bpf_prog_array_maps(trace);
+
+
if (trace->ev_qualifier_ids.nr > 0) {
err = trace__set_ev_qualifier_filter(trace);
if (err < 0)
@@ -3754,6 +3820,8 @@ static void trace__set_bpf_map_filtered_pids(struct trace *trace)
static void trace__set_bpf_map_syscalls(struct trace *trace)
{
trace->syscalls.map = trace__find_bpf_map_by_name(trace, "syscalls");
+ trace->syscalls.prog_array.sys_enter = trace__find_bpf_map_by_name(trace, "syscalls_sys_enter");
+ trace->syscalls.prog_array.sys_exit = trace__find_bpf_map_by_name(trace, "syscalls_sys_exit");
}

static int trace__config(const char *var, const char *value, void *arg)
diff --git a/tools/perf/examples/bpf/augmented_raw_syscalls.c b/tools/perf/examples/bpf/augmented_raw_syscalls.c
index 66b33b299349..c66474a6ccf4 100644
--- a/tools/perf/examples/bpf/augmented_raw_syscalls.c
+++ b/tools/perf/examples/bpf/augmented_raw_syscalls.c
@@ -33,6 +33,20 @@ struct syscall {

bpf_map(syscalls, ARRAY, int, struct syscall, 512);

+/*
+ * What to augment at entry?
+ *
+ * Pointer arg payloads (filenames, etc) passed from userspace to the kernel
+ */
+bpf_map(syscalls_sys_enter, PROG_ARRAY, u32, u32, 512);
+
+/*
+ * What to augment at exit?
+ *
+ * Pointer arg payloads returned from the kernel (struct stat, etc) to userspace.
+ */
+bpf_map(syscalls_sys_exit, PROG_ARRAY, u32, u32, 512);
+
struct syscall_enter_args {
unsigned long long common_tp_fields;
long syscall_nr;
--
2.21.0