tracing: probeevent: Add $argN for accessing function args

Add $argN special fetch variable for accessing function
arguments. This allows user to trace the Nth argument easily
at the function entry.

Note that this returns most probably assignment of registers
and stacks. In some case, it may not work well. If you need
to access correct registers or stacks you should use perf-probe.

Link: http://lkml.kernel.org/r/152465888632.26224.3412465701570253696.stgit@devbox

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 23 insertions, 13 deletions

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index dfd096031305..333cda6d2633 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -157,14 +157,13 @@ int traceprobe_split_symbol_offset(char *symbol, long *offset)
 #define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
 
 static int parse_probe_vars(char *arg, const struct fetch_type *t,
-			    struct fetch_insn *code, bool is_return,
-			    bool is_kprobe)
+			    struct fetch_insn *code, unsigned int flags)
 {
 	int ret = 0;
 	unsigned long param;
 
 	if (strcmp(arg, "retval") == 0) {
-		if (is_return)
+		if (flags & TPARG_FL_RETURN)
 			code->op = FETCH_OP_RETVAL;
 		else
 			ret = -EINVAL;
@@ -173,7 +172,8 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 			code->op = FETCH_OP_STACKP;
 		} else if (isdigit(arg[5])) {
 			ret = kstrtoul(arg + 5, 10, &param);
-			if (ret || (is_kprobe && param > PARAM_MAX_STACK))
+			if (ret || ((flags & TPARG_FL_KERNEL) &&
+				    param > PARAM_MAX_STACK))
 				ret = -EINVAL;
 			else {
 				code->op = FETCH_OP_STACK;
@@ -183,6 +183,18 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 			ret = -EINVAL;
 	} else if (strcmp(arg, "comm") == 0) {
 		code->op = FETCH_OP_COMM;
+#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
+	} else if (((flags & TPARG_FL_MASK) ==
+		    (TPARG_FL_KERNEL | TPARG_FL_FENTRY)) &&
+		   strncmp(arg, "arg", 3) == 0) {
+		if (!isdigit(arg[3]))
+			return -EINVAL;
+		ret = kstrtoul(arg + 3, 10, &param);
+		if (ret || !param || param > PARAM_MAX_STACK)
+			return -EINVAL;
+		code->op = FETCH_OP_ARG;
+		code->param = (unsigned int)param - 1;
+#endif
 	} else
 		ret = -EINVAL;
 
@@ -193,7 +205,7 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,
 static int
 parse_probe_arg(char *arg, const struct fetch_type *type,
 		struct fetch_insn **pcode, struct fetch_insn *end,
-		bool is_return, bool is_kprobe)
+		unsigned int flags)
 {
 	struct fetch_insn *code = *pcode;
 	unsigned long param;
@@ -203,8 +215,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 
 	switch (arg[0]) {
 	case '$':
-		ret = parse_probe_vars(arg + 1, type, code,
-					is_return, is_kprobe);
+		ret = parse_probe_vars(arg + 1, type, code, flags);
 		break;
 
 	case '%':	/* named register */
@@ -226,7 +237,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 			code->immediate = param;
 		} else if (arg[1] == '+') {
 			/* kprobes don't support file offsets */
-			if (is_kprobe)
+			if (flags & TPARG_FL_KERNEL)
 				return -EINVAL;
 
 			ret = kstrtol(arg + 2, 0, &offset);
@@ -237,7 +248,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 			code->immediate = (unsigned long)offset;  // imm64?
 		} else {
 			/* uprobes don't support symbols */
-			if (!is_kprobe)
+			if (!(flags & TPARG_FL_KERNEL))
 				return -EINVAL;
 
 			ret = traceprobe_split_symbol_offset(arg + 1, &offset);
@@ -278,8 +289,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 			const struct fetch_type *t2 = find_fetch_type(NULL);
 
 			*tmp = '\0';
-			ret = parse_probe_arg(arg, t2, &code, end, is_return,
-					      is_kprobe);
+			ret = parse_probe_arg(arg, t2, &code, end, flags);
 			if (ret)
 				break;
 			if (code->op == FETCH_OP_COMM)
@@ -339,7 +349,7 @@ static int __parse_bitfield_probe_arg(const char *bf,
 
 /* String length checking wrapper */
 int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
-		struct probe_arg *parg, bool is_return, bool is_kprobe)
+		struct probe_arg *parg, unsigned int flags)
 {
 	struct fetch_insn *code, *scode, *tmp = NULL;
 	char *t, *t2;
@@ -397,7 +407,7 @@ int traceprobe_parse_probe_arg(char *arg, ssize_t *size,
 	code[FETCH_INSN_MAX - 1].op = FETCH_OP_END;
 
 	ret = parse_probe_arg(arg, parg->type, &code, &code[FETCH_INSN_MAX - 1],
-			      is_return, is_kprobe);
+			      flags);
 	if (ret)
 		goto fail;