perf probe: Support tracing an entry of array

Add array-entry tracing support to perf probe. This enables to trace an entry
of array which is indexed by constant value, e.g. array[0].

For example:

  $ perf probe -a 'bio_split bi->bi_io_vec[0]'

Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100519195742.2885.5344.stgit@localhost6.localdomain6>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-probe.txt

@@ -94,7 +94,7 @@ Each probe argument follows below syntax.
 
  [NAME=]LOCALVAR|$retval|%REG|@SYMBOL[:TYPE]
 
-'NAME' specifies the name of this argument (optional). You can use the name of local variable, local data structure member (e.g. var->field, var.field2), or kprobe-tracer argument format (e.g. $retval, %ax, etc). Note that the name of this argument will be set as the last member name if you specify a local data structure member (e.g. field2 for 'var->field1.field2'.)
+'NAME' specifies the name of this argument (optional). You can use the name of local variable, local data structure member (e.g. var->field, var.field2), local array with fixed index (e.g. array[1], var->array[0], var->pointer[2]), or kprobe-tracer argument format (e.g. $retval, %ax, etc). Note that the name of this argument will be set as the last member name if you specify a local data structure member (e.g. field2 for 'var->field1.field2'.)
 'TYPE' casts the type of this argument (optional). If omitted, perf probe automatically set the type based on debuginfo. You can specify 'string' type only for the local variable or structure member which is an array of or a pointer to 'char' or 'unsigned char' type.
 
 LINE SYNTAX

tools/perf/util/probe-event.c

@@ -557,7 +557,7 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
 /* Parse perf-probe event argument */
 static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
 {
-	char *tmp;
+	char *tmp, *goodname;
 	struct perf_probe_arg_field **fieldp;
 
 	pr_debug("parsing arg: %s into ", str);
@@ -580,7 +580,7 @@ static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
 		pr_debug("type:%s ", arg->type);
 	}
 
-	tmp = strpbrk(str, "-.");
+	tmp = strpbrk(str, "-.[");
 	if (!is_c_varname(str) || !tmp) {
 		/* A variable, register, symbol or special value */
 		arg->var = strdup(str);
@@ -590,10 +590,11 @@ static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
 		return 0;
 	}
 
-	/* Structure fields */
+	/* Structure fields or array element */
 	arg->var = strndup(str, tmp - str);
 	if (arg->var == NULL)
 		return -ENOMEM;
+	goodname = arg->var;
 	pr_debug("%s, ", arg->var);
 	fieldp = &arg->field;
 
@@ -601,6 +602,19 @@ static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
 		*fieldp = zalloc(sizeof(struct perf_probe_arg_field));
 		if (*fieldp == NULL)
 			return -ENOMEM;
+		if (*tmp == '[') {	/* Array */
+			str = tmp;
+			(*fieldp)->index = strtol(str + 1, &tmp, 0);
+			(*fieldp)->ref = true;
+			if (*tmp != ']' || tmp == str + 1) {
+				semantic_error("Array index must be a"
+						" number.\n");
+				return -EINVAL;
+			}
+			tmp++;
+			if (*tmp == '\0')
+				tmp = NULL;
+		} else {		/* Structure */
 			if (*tmp == '.') {
 				str = tmp + 1;
 				(*fieldp)->ref = false;
@@ -608,15 +622,18 @@ static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
 				str = tmp + 2;
 				(*fieldp)->ref = true;
 			} else {
-			semantic_error("Argument parse error: %s\n", str);
+				semantic_error("Argument parse error: %s\n",
+					       str);
 				return -EINVAL;
 			}
-
-		tmp = strpbrk(str, "-.");
+			tmp = strpbrk(str, "-.[");
+		}
 		if (tmp) {
 			(*fieldp)->name = strndup(str, tmp - str);
 			if ((*fieldp)->name == NULL)
 				return -ENOMEM;
+			if (*str != '[')
+				goodname = (*fieldp)->name;
 			pr_debug("%s(%d), ", (*fieldp)->name, (*fieldp)->ref);
 			fieldp = &(*fieldp)->next;
 		}
@@ -624,11 +641,13 @@ static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
 	(*fieldp)->name = strdup(str);
 	if ((*fieldp)->name == NULL)
 		return -ENOMEM;
+	if (*str != '[')
+		goodname = (*fieldp)->name;
 	pr_debug("%s(%d)\n", (*fieldp)->name, (*fieldp)->ref);
 
-	/* If no name is specified, set the last field name */
+	/* If no name is specified, set the last field name (not array index)*/
 	if (!arg->name) {
-		arg->name = strdup((*fieldp)->name);
+		arg->name = strdup(goodname);
 		if (arg->name == NULL)
 			return -ENOMEM;
 	}
@@ -776,8 +795,11 @@ int synthesize_perf_probe_arg(struct perf_probe_arg *pa, char *buf, size_t len)
 	len -= ret;
 
 	while (field) {
-		ret = e_snprintf(tmp, len, "%s%s", field->ref ? "->" : ".",
-				 field->name);
+		if (field->name[0] == '[')
+			ret = e_snprintf(tmp, len, "%s", field->name);
+		else
+			ret = e_snprintf(tmp, len, "%s%s",
+					 field->ref ? "->" : ".", field->name);
 		if (ret <= 0)
 			goto error;
 		tmp += ret;

tools/perf/util/probe-event.h

@@ -50,6 +50,7 @@ struct perf_probe_point {
 struct perf_probe_arg_field {
 	struct perf_probe_arg_field	*next;	/* Next field */
 	char				*name;	/* Name of the field */
+	long				index;	/* Array index number */
 	bool				ref;	/* Referencing flag */
 };
 

tools/perf/util/probe-finder.c

@@ -485,6 +485,9 @@ static int convert_variable_type(Dwarf_Die *vr_die,
 		return -ENOENT;
 	}
 
+	pr_debug("%s type is %s.\n",
+		 dwarf_diename(vr_die), dwarf_diename(&type));
+
 	if (cast && strcmp(cast, "string") == 0) {	/* String type */
 		ret = dwarf_tag(&type);
 		if (ret != DW_TAG_pointer_type &&
@@ -553,16 +556,44 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 	struct kprobe_trace_arg_ref *ref = *ref_ptr;
 	Dwarf_Die type;
 	Dwarf_Word offs;
-	int ret;
+	int ret, tag;
 
 	pr_debug("converting %s in %s\n", field->name, varname);
 	if (die_get_real_type(vr_die, &type) == NULL) {
 		pr_warning("Failed to get the type of %s.\n", varname);
 		return -ENOENT;
 	}
+	pr_debug2("Var real type: (%x)\n", (unsigned)dwarf_dieoffset(&type));
+	tag = dwarf_tag(&type);
 
+	if (field->name[0] == '[' &&
+	    (tag == DW_TAG_array_type || tag == DW_TAG_pointer_type)) {
+		if (field->next)
+			/* Save original type for next field */
+			memcpy(die_mem, &type, sizeof(*die_mem));
+		/* Get the type of this array */
+		if (die_get_real_type(&type, &type) == NULL) {
+			pr_warning("Failed to get the type of %s.\n", varname);
+			return -ENOENT;
+		}
+		pr_debug2("Array real type: (%x)\n",
+			 (unsigned)dwarf_dieoffset(&type));
+		if (tag == DW_TAG_pointer_type) {
+			ref = zalloc(sizeof(struct kprobe_trace_arg_ref));
+			if (ref == NULL)
+				return -ENOMEM;
+			if (*ref_ptr)
+				(*ref_ptr)->next = ref;
+			else
+				*ref_ptr = ref;
+		}
+		ref->offset += die_get_byte_size(&type) * field->index;
+		if (!field->next)
+			/* Save vr_die for converting types */
+			memcpy(die_mem, vr_die, sizeof(*die_mem));
+		goto next;
+	} else if (tag == DW_TAG_pointer_type) {
 		/* Check the pointer and dereference */
-	if (dwarf_tag(&type) == DW_TAG_pointer_type) {
 		if (!field->ref) {
 			pr_err("Semantic error: %s must be referred by '->'\n",
 			       field->name);
@@ -588,10 +619,15 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 			*ref_ptr = ref;
 	} else {
 		/* Verify it is a data structure  */
-		if (dwarf_tag(&type) != DW_TAG_structure_type) {
+		if (tag != DW_TAG_structure_type) {
 			pr_warning("%s is not a data structure.\n", varname);
 			return -EINVAL;
 		}
+		if (field->name[0] == '[') {
+			pr_err("Semantic error: %s is not a pointor nor array.",
+			       varname);
+			return -EINVAL;
+		}
 		if (field->ref) {
 			pr_err("Semantic error: %s must be referred by '.'\n",
 			       field->name);
@@ -618,6 +654,7 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 	}
 	ref->offset += (long)offs;
 
+next:
 	/* Converting next field */
 	if (field->next)
 		return convert_variable_fields(die_mem, field->name,
@@ -667,7 +704,6 @@ static int find_variable(Dwarf_Die *sp_die, struct probe_finder *pf)
 	char buf[32], *ptr;
 	int ret;
 
-	/* TODO: Support arrays */
 	if (pf->pvar->name)
 		pf->tvar->name = strdup(pf->pvar->name);
 	else {