Message-ID:  <168407353144.941486.592643565749157905.stgit@mhiramat.roam.corp.google.com>
Date:   Sun, 14 May 2023 23:12:11 +0900
From:   "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To:     linux-trace-kernel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        mhiramat@...nel.org, Florent Revest <revest@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>, bpf@...r.kernel.org
Subject: [PATCH v10 07/11] tracing/probes: Add $args meta argument for all function args

From: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Add the '$args' meta fetch argument for function-entry probe events. This
will be expanded to the all arguments of the function and the tracepoint
using BTF function argument information.

e.g.
 #  echo 'p vfs_read $args' >> dynamic_events
 #  echo 'f vfs_write $args' >> dynamic_events
 #  echo 't sched_overutilized_tp $args' >> dynamic_events
 # cat dynamic_events
p:kprobes/p_vfs_read_0 vfs_read file=file buf=buf count=count pos=pos
f:fprobes/vfs_write__entry vfs_write file=file buf=buf count=count pos=pos
t:tracepoints/sched_overutilized_tp sched_overutilized_tp rd=rd overutilized=overutilized

NOTE: This is not like other $-vars, you can not use this $args as a
part of fetch args, e.g. specifying name "foo=$args" and using it in
dereferences "+0($args)" will lead a parse error.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
Changes in v10:
 - Change $$args to $args so that user can use $$ for current task's pid.
Changes in v6:
 - update patch description.
---
 kernel/trace/trace_fprobe.c |   21 ++++++++-
 kernel/trace/trace_kprobe.c |   23 ++++++++--
 kernel/trace/trace_probe.c  |   98 +++++++++++++++++++++++++++++++++++++++++++
 kernel/trace/trace_probe.h  |   10 ++++
 4 files changed, 144 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index 75130a5bdddc..6573e93e7631 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -925,14 +925,16 @@ static int __trace_fprobe_create(int argc, const char *argv[])
 	 *  FETCHARG:TYPE : use TYPE instead of unsigned long.
 	 */
 	struct trace_fprobe *tf = NULL;
-	int i, len, ret = 0;
+	int i, len, new_argc = 0, ret = 0;
 	bool is_return = false;
 	char *symbol = NULL, *tmp = NULL;
 	const char *event = NULL, *group = FPROBE_EVENT_SYSTEM;
+	const char **new_argv = NULL;
 	int maxactive = 0;
 	char buf[MAX_EVENT_NAME_LEN];
 	char gbuf[MAX_EVENT_NAME_LEN];
 	char sbuf[KSYM_NAME_LEN];
+	char abuf[MAX_BTF_ARGS_LEN];
 	bool is_tracepoint = false;
 	struct tracepoint *tpoint = NULL;
 	struct traceprobe_parse_context ctx = {
@@ -1038,9 +1040,22 @@ static int __trace_fprobe_create(int argc, const char *argv[])
 	} else
 		ctx.funcname = symbol;
 
+	argc -= 2; argv += 2;
+	new_argv = traceprobe_expand_meta_args(argc, argv, &new_argc,
+					       abuf, MAX_BTF_ARGS_LEN, &ctx);
+	if (IS_ERR(new_argv)) {
+		ret = PTR_ERR(new_argv);
+		new_argv = NULL;
+		goto out;
+	}
+	if (new_argv) {
+		argc = new_argc;
+		argv = new_argv;
+	}
+
 	/* setup a probe */
 	tf = alloc_trace_fprobe(group, event, symbol, tpoint, maxactive,
-				argc - 2, is_return);
+				argc, is_return);
 	if (IS_ERR(tf)) {
 		ret = PTR_ERR(tf);
 		/* This must return -ENOMEM, else there is a bug */
@@ -1052,7 +1067,6 @@ static int __trace_fprobe_create(int argc, const char *argv[])
 		tf->mod = __module_text_address(
 				(unsigned long)tf->tpoint->probestub);
 
-	argc -= 2; argv += 2;
 	/* parse arguments */
 	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
 		trace_probe_log_set_index(i + 2);
@@ -1081,6 +1095,7 @@ static int __trace_fprobe_create(int argc, const char *argv[])
 
 out:
 	trace_probe_log_clear();
+	kfree(new_argv);
 	kfree(symbol);
 	return ret;
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index aff6c1a5e161..2d7c0188c2b1 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -732,9 +732,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 	 *  FETCHARG:TYPE : use TYPE instead of unsigned long.
 	 */
 	struct trace_kprobe *tk = NULL;
-	int i, len, ret = 0;
+	int i, len, new_argc = 0, ret = 0;
 	bool is_return = false;
 	char *symbol = NULL, *tmp = NULL;
+	const char **new_argv = NULL;
 	const char *event = NULL, *group = KPROBE_EVENT_SYSTEM;
 	enum probe_print_type ptype;
 	int maxactive = 0;
@@ -742,6 +743,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 	void *addr = NULL;
 	char buf[MAX_EVENT_NAME_LEN];
 	char gbuf[MAX_EVENT_NAME_LEN];
+	char abuf[MAX_BTF_ARGS_LEN];
 	struct traceprobe_parse_context ctx = { .flags = TPARG_FL_KERNEL };
 
 	switch (argv[0][0]) {
@@ -854,19 +856,31 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 		event = buf;
 	}
 
+	argc -= 2; argv += 2;
+	ctx.funcname = symbol;
+	new_argv = traceprobe_expand_meta_args(argc, argv, &new_argc,
+					       abuf, MAX_BTF_ARGS_LEN, &ctx);
+	if (IS_ERR(new_argv)) {
+		ret = PTR_ERR(new_argv);
+		new_argv = NULL;
+		goto out;
+	}
+	if (new_argv) {
+		argc = new_argc;
+		argv = new_argv;
+	}
+
 	/* setup a probe */
 	tk = alloc_trace_kprobe(group, event, addr, symbol, offset, maxactive,
-				argc - 2, is_return);
+				argc, is_return);
 	if (IS_ERR(tk)) {
 		ret = PTR_ERR(tk);
 		/* This must return -ENOMEM, else there is a bug */
 		WARN_ON_ONCE(ret != -ENOMEM);
 		goto out;	/* We know tk is not allocated */
 	}
-	argc -= 2; argv += 2;
 
 	/* parse arguments */
-	ctx.funcname = symbol;
 	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
 		trace_probe_log_set_index(i + 2);
 		ctx.offset = 0;
@@ -894,6 +908,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
 
 out:
 	trace_probe_log_clear();
+	kfree(new_argv);
 	kfree(symbol);
 	return ret;
 
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 525341c42851..ef9866dcae1f 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -451,12 +451,18 @@ static const struct fetch_type *parse_btf_arg_type(int arg_idx,
 
 	return find_fetch_type(typestr, ctx->flags);
 }
+
 #else
 static struct btf *traceprobe_get_btf(void)
 {
 	return NULL;
 }
 
+static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
 static int parse_btf_arg(const char *varname, struct fetch_insn *code,
 			 struct traceprobe_parse_context *ctx)
 {
@@ -535,6 +541,11 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
 	len = str_has_prefix(arg, "arg");
 	if (len && tparg_is_function_entry(ctx->flags)) {
+		if (strcmp(arg, "args") == 0) {
+			err = TP_ERR_BAD_VAR_ARGS;
+			goto inval;
+		}
+
 		ret = kstrtoul(arg + len, 10, &param);
 		if (ret)
 			goto inval;
@@ -1094,6 +1105,93 @@ void traceprobe_free_probe_arg(struct probe_arg *arg)
 	kfree(arg->fmt);
 }
 
+/* Return new_argv which must be freed after use */
+const char **traceprobe_expand_meta_args(int argc, const char *argv[],
+					 int *new_argc, char *buf, int bufsize,
+					 struct traceprobe_parse_context *ctx)
+{
+	struct btf *btf = traceprobe_get_btf();
+	const struct btf_param *params = NULL;
+	int i, j, used, ret, args_idx = -1;
+	const char **new_argv = NULL;
+	int nr_skipped;
+
+	/* The first argument of tracepoint should be skipped. */
+	nr_skipped = ctx->flags & TPARG_FL_TPOINT ? 1 : 0;
+	for (i = 0; i < argc; i++)
+		if (!strcmp(argv[i], "$args")) {
+			trace_probe_log_set_index(i + 2);
+
+			if (!tparg_is_function_entry(ctx->flags)) {
+				trace_probe_log_err(0, NOFENTRY_ARGS);
+				return ERR_PTR(-EINVAL);
+			}
+
+			if (args_idx >= 0) {
+				trace_probe_log_err(0, DOUBLE_ARGS);
+				return ERR_PTR(-EINVAL);
+			}
+
+			args_idx = i;
+			params = find_btf_func_param(ctx->funcname, &ctx->nr_params);
+			if (IS_ERR(params)) {
+				trace_probe_log_err(0, NOSUP_BTFARG);
+				return (const char **)params;
+			}
+			ctx->params = params;
+		}
+
+	/* If target has no arguments, return NULL and the original argc. */
+	if (args_idx < 0 || ctx->nr_params < nr_skipped) {
+		*new_argc = argc;
+		return NULL;
+	}
+
+	*new_argc = argc - 1 + ctx->nr_params - nr_skipped;
+
+	new_argv = kcalloc(*new_argc, sizeof(char *), GFP_KERNEL);
+	if (!new_argv)
+		return ERR_PTR(-ENOMEM);
+
+	for (i = 0; i < args_idx; i++)
+		new_argv[i] = argv[i];
+
+	used = 0;
+	trace_probe_log_set_index(args_idx + 2);
+	for (i = 0; i < ctx->nr_params - nr_skipped; i++) {
+		const char *name;
+
+		name = btf_name_by_offset(btf, params[i + nr_skipped].name_off);
+		if (!name) {
+			trace_probe_log_err(0, NO_BTF_ENTRY);
+			ret = -ENOENT;
+			goto error;
+		}
+		ret = snprintf(buf + used, bufsize - used, "%s", name);
+		if (ret >= bufsize - used) {
+			trace_probe_log_err(0, ARGS_2LONG);
+			ret = -E2BIG;
+			goto error;
+		}
+		new_argv[args_idx + i] = buf + used;
+		used += ret + 1; /* include null byte */
+	}
+
+	/* Note: we have to skip $$args */
+	j = args_idx + ctx->nr_params - nr_skipped;
+	for (i = args_idx + 1; i < argc; i++, j++) {
+		if (WARN_ON(j >= *new_argc))
+			goto error;
+		new_argv[j] = argv[i];
+	}
+
+	return new_argv;
+
+error:
+	kfree(new_argv);
+	return ERR_PTR(ret);
+}
+
 int traceprobe_update_arg(struct probe_arg *arg)
 {
 	struct fetch_insn *code = arg->code;
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 9ea5c7e8753f..da91ce4b8a40 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -33,6 +33,7 @@
 #define MAX_ARGSTR_LEN		63
 #define MAX_ARRAY_LEN		64
 #define MAX_ARG_NAME_LEN	32
+#define MAX_BTF_ARGS_LEN	128
 #define MAX_STRING_SIZE		PATH_MAX
 
 /* Reserved field names */
@@ -387,6 +388,9 @@ struct traceprobe_parse_context {
 extern int traceprobe_parse_probe_arg(struct trace_probe *tp, int i,
 				      const char *argv,
 				      struct traceprobe_parse_context *ctx);
+const char **traceprobe_expand_meta_args(int argc, const char *argv[],
+					 int *new_argc, char *buf, int bufsize,
+					 struct traceprobe_parse_context *ctx);
 
 extern int traceprobe_update_arg(struct probe_arg *arg);
 extern void traceprobe_free_probe_arg(struct probe_arg *arg);
@@ -481,7 +485,11 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
 	C(NO_EP_FILTER,		"No filter rule after 'if'"),		\
 	C(NOSUP_BTFARG,		"BTF is not available or not supported"),	\
 	C(NO_BTFARG,		"This variable is not found at this probe point"),\
-	C(NO_BTF_ENTRY,		"No BTF entry for this probe point"),
+	C(NO_BTF_ENTRY,		"No BTF entry for this probe point"),	\
+	C(BAD_VAR_ARGS,		"$args must be an independent parameter without name etc."),\
+	C(NOFENTRY_ARGS,	"$args can be used only on function entry"),	\
+	C(DOUBLE_ARGS,		"$args can be used only once in the parameters"),	\
+	C(ARGS_2LONG,		"$args failed because the argument is too long"),
 
 #undef C
 #define C(a, b)		TP_ERR_##a

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