perf trace: Add trace__bpf_sys_enter_beauty_map() to prepare for fetching data in BPF

Set up beauty_map, load it to BPF, in such format: if argument No.3 is a
struct of size 32 bytes (of syscall number 114) beauty_map[114][2] = 32;

if argument No.3 is a string (of syscall number 114) beauty_map[114][2] =
1;

if argument No.3 is a buffer, its size is indicated by argument No.4 (of
syscall number 114) beauty_map[114][2] = -4; /* -1 ~ -6, we'll read this
buffer size in BPF */

Committer notes:

Moved syscall_arg_fmt__cache_btf_struct() from a ifdef
HAVE_LIBBPF_SUPPORT to closer to where it is used, that is ifdef'ed on
HAVE_BPF_SKEL and thus breaks the build when building with
BUILD_BPF_SKEL=0, as detected using 'make -C tools/perf build-test'.

Also add 'struct beauty_map_enter' to tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
as we're using it in this patch, otherwise we get this while trying to
build at this point in the original patch series:

builtin-trace.c: In function ‘trace__init_syscalls_bpf_prog_array_maps’:
builtin-trace.c:3725:58: error: ‘struct <anonymous>’ has no member named ‘beauty_map_enter’
3725 | int beauty_map_fd = bpf_map__fd(trace->skel->maps.beauty_map_enter);
|

We also have to take into account syscall_arg_fmt.from_user when telling
the kernel what to copy in the sys_enter generic collector, we don't
want to collect bogus data in buffers that will only be available to us
at sys_exit time, i.e. after the kernel has filled it, so leave this for
when we have such a sys_exit based collector.

Committer testing:

Not wired up yet, so all continues to work, using the existing BPF
collector and userspace beautifiers that are augmentation aware:

root@number:~# rm -f 987654 ; touch 123456 ; perf trace -e rename* mv 123456 987654
0.000 ( 0.031 ms): mv/20888 renameat2(olddfd: CWD, oldname: "123456", newdfd: CWD, newname: "987654", flags: NOREPLACE) = 0
root@number:~# perf trace -e connect,sendto ping -c 1 www.google.com
0.000 ( 0.014 ms): ping/20892 connect(fd: 5, uservaddr: { .family: LOCAL, path: /run/systemd/resolve/io.systemd.Resolve }, addrlen: 42) = 0
0.040 ( 0.003 ms): ping/20892 sendto(fd: 5, buff: 0x560b4ff17980, len: 97, flags: DONTWAIT|NOSIGNAL) = 97
0.480 ( 0.017 ms): ping/20892 sendto(fd: 5, buff: 0x7ffd82d07150, len: 20, addr: { .family: NETLINK }, addr_len: 0xc) = 20
0.526 ( 0.014 ms): ping/20892 connect(fd: 5, uservaddr: { .family: INET6, port: 0, addr: 2800:3f0:4004:810::2004 }, addrlen: 28) = 0
0.542 ( 0.002 ms): ping/20892 connect(fd: 5, uservaddr: { .family: UNSPEC }, addrlen: 16) = 0
0.544 ( 0.004 ms): ping/20892 connect(fd: 5, uservaddr: { .family: INET, port: 0, addr: 142.251.135.100 }, addrlen: 16) = 0
0.559 ( 0.002 ms): ping/20892 connect(fd: 5, uservaddr: { .family: INET, port: 1025, addr: 142.251.135.100 }, addrlen: 16PING www.google.com (142.251.135.100) 56(84) bytes of data.
) = 0
0.589 ( 0.058 ms): ping/20892 sendto(fd: 3, buff: 0x560b4ff11ac0, len: 64, addr: { .family: INET, port: 0, addr: 142.251.135.100 }, addr_len: 0x10) = 64
45.250 ( 0.029 ms): ping/20892 connect(fd: 5, uservaddr: { .family: LOCAL, path: /run/systemd/resolve/io.systemd.Resolve }, addrlen: 42) = 0
45.344 ( 0.012 ms): ping/20892 sendto(fd: 5, buff: 0x560b4ff19340, len: 111, flags: DONTWAIT|NOSIGNAL) = 111
64 bytes from rio09s08-in-f4.1e100.net (142.251.135.100): icmp_seq=1 ttl=49 time=44.4 ms

--- www.google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 44.361/44.361/44.361/0.000 ms
root@number:~#

Signed-off-by: Howard Chu <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-trace.c

···
 	bool	   show_zero;
 #ifdef HAVE_LIBBPF_SUPPORT
 	const struct btf_type *type;
+	int	   type_id; /* used in btf_dump */
 #endif
 };
 
···
 }
 
 #ifdef HAVE_BPF_SKEL
+static int syscall_arg_fmt__cache_btf_struct(struct syscall_arg_fmt *arg_fmt, struct btf *btf, char *type)
+{
+       int id;
+
+	if (arg_fmt->type != NULL)
+		return -1;
+
+       id = btf__find_by_name(btf, type);
+       if (id < 0)
+		return -1;
+
+       arg_fmt->type    = btf__type_by_id(btf, id);
+       arg_fmt->type_id = id;
+
+       return 0;
+}
+
 static struct bpf_program *trace__find_bpf_program_by_title(struct trace *trace, const char *name)
 {
 	struct bpf_program *pos, *prog = NULL;
···
 {
 	struct syscall *sc = trace__syscall_info(trace, NULL, id);
 	return sc ? bpf_program__fd(sc->bpf_prog.sys_exit) : bpf_program__fd(trace->skel->progs.syscall_unaugmented);
+}
+
+static int trace__bpf_sys_enter_beauty_map(struct trace *trace, int key, unsigned int *beauty_array)
+{
+	struct tep_format_field *field;
+	struct syscall *sc = trace__syscall_info(trace, NULL, key);
+	const struct btf_type *bt;
+	char *struct_offset, *tmp, name[32];
+	bool can_augment = false;
+	int i, cnt;
+
+	if (sc == NULL)
+		return -1;
+
+	trace__load_vmlinux_btf(trace);
+	if (trace->btf == NULL)
+		return -1;
+
+	for (i = 0, field = sc->args; field; ++i, field = field->next) {
+		struct_offset = strstr(field->type, "struct ");
+
+		// XXX We're only collecting pointer payloads _from_ user space
+		if (!sc->arg_fmt[i].from_user)
+			continue;
+
+		if (field->flags & TEP_FIELD_IS_POINTER && struct_offset) { /* struct */
+			struct_offset += 7;
+
+			/* for 'struct foo *', we only want 'foo' */
+			for (tmp = struct_offset, cnt = 0; *tmp != ' ' && *tmp != '\0'; ++tmp, ++cnt) {
+			}
+
+			strncpy(name, struct_offset, cnt);
+			name[cnt] = '\0';
+
+			/* cache struct's btf_type and type_id */
+			if (syscall_arg_fmt__cache_btf_struct(&sc->arg_fmt[i], trace->btf, name))
+				continue;
+
+			bt = sc->arg_fmt[i].type;
+			beauty_array[i] = bt->size;
+			can_augment = true;
+		} else if (field->flags & TEP_FIELD_IS_POINTER && /* string */
+			   strcmp(field->type, "const char *") == 0 &&
+			   (strstr(field->name, "name") ||
+			    strstr(field->name, "path") ||
+			    strstr(field->name, "file") ||
+			    strstr(field->name, "root") ||
+			    strstr(field->name, "key") ||
+			    strstr(field->name, "special") ||
+			    strstr(field->name, "type") ||
+			    strstr(field->name, "description"))) {
+			beauty_array[i] = 1;
+			can_augment = true;
+		} else if (field->flags & TEP_FIELD_IS_POINTER && /* buffer */
+			   strstr(field->type, "char *") &&
+			   (strstr(field->name, "buf") ||
+			    strstr(field->name, "val") ||
+			    strstr(field->name, "msg"))) {
+			int j;
+			struct tep_format_field *field_tmp;
+
+			/* find the size of the buffer that appears in pairs with buf */
+			for (j = 0, field_tmp = sc->args; field_tmp; ++j, field_tmp = field_tmp->next) {
+				if (!(field_tmp->flags & TEP_FIELD_IS_POINTER) && /* only integers */
+				    (strstr(field_tmp->name, "count") ||
+				     strstr(field_tmp->name, "siz") ||  /* size, bufsiz */
+				     (strstr(field_tmp->name, "len") && strcmp(field_tmp->name, "filename")))) {
+					 /* filename's got 'len' in it, we don't want that */
+					beauty_array[i] = -(j + 1);
+					can_augment = true;
+					break;
+				}
+			}
+		}
+	}
+
+	if (can_augment)
+		return 0;
+
+	return -1;
 }
 
 static struct bpf_program *trace__find_usable_bpf_prog_entry(struct trace *trace, struct syscall *sc)
···
 {
 	int map_enter_fd = bpf_map__fd(trace->skel->maps.syscalls_sys_enter);
 	int map_exit_fd  = bpf_map__fd(trace->skel->maps.syscalls_sys_exit);
+	int beauty_map_fd = bpf_map__fd(trace->skel->maps.beauty_map_enter);
 	int err = 0;
+	unsigned int beauty_array[6];
 
 	for (int i = 0; i < trace->sctbl->syscalls.nr_entries; ++i) {
 		int prog_fd, key = syscalltbl__id_at_idx(trace->sctbl, i);
···
 			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;
+
+		/* use beauty_map to tell BPF how many bytes to collect, set beauty_map's value here */
+		memset(beauty_array, 0, sizeof(beauty_array));
+		err = trace__bpf_sys_enter_beauty_map(trace, key, (unsigned int *)beauty_array);
+		if (err)
+			continue;
+		err = bpf_map_update_elem(beauty_map_fd, &key, beauty_array, BPF_ANY);
 		if (err)
 			break;
 	}

tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c

···
 	__uint(max_entries, 1);
 } augmented_args_tmp SEC(".maps");
 
+struct beauty_map_enter {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, int);
+	__type(value, __u32[6]);
+	__uint(max_entries, 512);
+} beauty_map_enter SEC(".maps");
+
 static inline struct augmented_args_payload *augmented_args_payload(void)
 {
 	int key = 0;