perf augmented_raw_syscalls: Tell which args are filenames and how many bytes to copy

Since we know what args are strings from reading the syscall
descriptions in tracefs and also already mark such args to be beautified
using the syscall_arg__scnprintf_filename() helper, all we need is to
fill in this info in the 'syscalls' BPF map we were using to state which
syscalls the user is interested in, i.e. the syscall filter.

Right now just set that with PATH_MAX and unroll the syscall arg in the
BPF program, as the verifier isn't liking something clang generates when
unrolling the loop.

This also makes the augmented_raw_syscalls.c program support all arches,
since we removed that set of defines with the hard coded syscall
numbers, all should be automatically set for all arches, with the
syscall id mapping done correcly.

Doing baby steps here, i.e. just the first string arg for a syscall is
printed, syscalls with more than one, say, the various rename* syscalls,
need further work, but lets get first something that the BPF verifier
accepts before increasing the complexity

To test it, something like:

 # perf trace -e string -e /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.c

With:

  # cat ~/.perfconfig
  [llvm]
	dump-obj = true
	clang-opt = -g
  [trace]
	#add_events = /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.c
	show_zeros = yes
	show_duration = no
	no_inherit = yes
	show_timestamp = no
	show_arg_names = no
	args_alignment = 40
	show_prefix = yes
  #

That commented add_events line is needed for developing this
augmented_raw_syscalls.c BPF program, as if we add it via the
'add_events' mechanism so as to shorten the 'perf trace' command lines,
then we end up not setting up the -v option which precludes us having
access to the bpf verifier log :-\

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Link: https://lkml.kernel.org/n/tip-dn863ya0cbsqycxuy0olvbt1@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 31 insertions, 0 deletions

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index 54b2d0fd0d02..19f22127f02e 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -972,8 +972,14 @@ struct syscall {
 	struct syscall_arg_fmt *arg_fmt;
 };
 
+/*
+ * Must match what is in the BPF program:
+ *
+ * tools/perf/examples/bpf/augmented_raw_syscalls.c
+ */
 struct bpf_map_syscall_entry {
 	bool	enabled;
+	u16	string_args_len[6];
 };
 
 /*
@@ -2711,6 +2717,25 @@ out_enomem:
 }
 
 #ifdef HAVE_LIBBPF_SUPPORT
+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);
+	int arg = 0;
+
+	if (sc == NULL)
+		goto out;
+
+	for (; arg < sc->nr_args; ++arg) {
+		entry->string_args_len[arg] = 0;
+		if (sc->arg_fmt[arg].scnprintf == SCA_FILENAME) {
+			/* Should be set like strace -s strsize */
+			entry->string_args_len[arg] = PATH_MAX;
+		}
+	}
+out:
+	for (; arg < 6; ++arg)
+		entry->string_args_len[arg] = 0;
+}
 static int trace__set_ev_qualifier_bpf_filter(struct trace *trace)
 {
 	int fd = bpf_map__fd(trace->syscalls.map);
@@ -2723,6 +2748,9 @@ static int trace__set_ev_qualifier_bpf_filter(struct trace *trace)
 	for (i = 0; i < trace->ev_qualifier_ids.nr; ++i) {
 		int key = trace->ev_qualifier_ids.entries[i];
 
+		if (value.enabled)
+			trace__init_bpf_map_syscall_args(trace, key, &value);
+
 		err = bpf_map_update_elem(fd, &key, &value, BPF_EXIST);
 		if (err)
 			break;
@@ -2740,6 +2768,9 @@ 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)
+			trace__init_bpf_map_syscall_args(trace, key, &value);
+
 		err = bpf_map_update_elem(fd, &key, &value, BPF_ANY);
 		if (err)
 			break;