perf probe: Show accessible local variables

Add -V (--vars) option for listing accessible local variables at given probe
point. This will help finding which local variables are available for event
arguments.

e.g.)
 # perf probe -V call_timer_fn:23
 Available variables at call_timer_fn:23
         @<run_timer_softirq+345>
                 function_type*  fn
                 int     preempt_count
                 long unsigned int       data
                 struct list_head        work_list
                 struct list_head*       head
                 struct timer_list*      timer
                 struct tvec_base*       base

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20101021101323.3542.40282.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-finder.c

@@ -172,8 +172,8 @@ static Dwarf_Die *die_get_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
 		return NULL;
 }
 
-/* Get type die, but skip qualifiers and typedef */
-static Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
+/* Get a type die, but skip qualifiers */
+static Dwarf_Die *__die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
 {
 	int tag;
 
@@ -185,8 +185,17 @@ static Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
 	} while (tag == DW_TAG_const_type ||
 		 tag == DW_TAG_restrict_type ||
 		 tag == DW_TAG_volatile_type ||
-		 tag == DW_TAG_shared_type ||
-		 tag == DW_TAG_typedef);
+		 tag == DW_TAG_shared_type);
+
+	return vr_die;
+}
+
+/* Get a type die, but skip qualifiers and typedef */
+static Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
+{
+	do {
+		vr_die = __die_get_real_type(vr_die, die_mem);
+	} while (vr_die && dwarf_tag(vr_die) == DW_TAG_typedef);
 
 	return vr_die;
 }
@@ -380,6 +389,60 @@ static Dwarf_Die *die_find_member(Dwarf_Die *st_die, const char *name,
 			      die_mem);
 }
 
+/* Get the name of given variable DIE */
+static int die_get_typename(Dwarf_Die *vr_die, char *buf, int len)
+{
+	Dwarf_Die type;
+	int tag, ret, ret2;
+	const char *tmp = "";
+
+	if (__die_get_real_type(vr_die, &type) == NULL)
+		return -ENOENT;
+
+	tag = dwarf_tag(&type);
+	if (tag == DW_TAG_array_type || tag == DW_TAG_pointer_type)
+		tmp = "*";
+	else if (tag == DW_TAG_subroutine_type) {
+		/* Function pointer */
+		ret = snprintf(buf, len, "(function_type)");
+		return (ret >= len) ? -E2BIG : ret;
+	} else {
+		if (!dwarf_diename(&type))
+			return -ENOENT;
+		if (tag == DW_TAG_union_type)
+			tmp = "union ";
+		else if (tag == DW_TAG_structure_type)
+			tmp = "struct ";
+		/* Write a base name */
+		ret = snprintf(buf, len, "%s%s", tmp, dwarf_diename(&type));
+		return (ret >= len) ? -E2BIG : ret;
+	}
+	ret = die_get_typename(&type, buf, len);
+	if (ret > 0) {
+		ret2 = snprintf(buf + ret, len - ret, "%s", tmp);
+		ret = (ret2 >= len - ret) ? -E2BIG : ret2 + ret;
+	}
+	return ret;
+}
+
+/* Get the name and type of given variable DIE, stored as "type\tname" */
+static int die_get_varname(Dwarf_Die *vr_die, char *buf, int len)
+{
+	int ret, ret2;
+
+	ret = die_get_typename(vr_die, buf, len);
+	if (ret < 0) {
+		pr_debug("Failed to get type, make it unknown.\n");
+		ret = snprintf(buf, len, "(unknown_type)");
+	}
+	if (ret > 0) {
+		ret2 = snprintf(buf + ret, len - ret, "\t%s",
+				dwarf_diename(vr_die));
+		ret = (ret2 >= len - ret) ? -E2BIG : ret2 + ret;
+	}
+	return ret;
+}
+
 /*
  * Probe finder related functions
  */
@@ -393,8 +456,13 @@ static struct probe_trace_arg_ref *alloc_trace_arg_ref(long offs)
 	return ref;
 }
 
-/* Show a location */
-static int convert_variable_location(Dwarf_Die *vr_die, struct probe_finder *pf)
+/*
+ * Convert a location into trace_arg.
+ * If tvar == NULL, this just checks variable can be converted.
+ */
+static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
+				     Dwarf_Op *fb_ops,
+				     struct probe_trace_arg *tvar)
 {
 	Dwarf_Attribute attr;
 	Dwarf_Op *op;
@@ -403,7 +471,6 @@ static int convert_variable_location(Dwarf_Die *vr_die, struct probe_finder *pf)
 	Dwarf_Word offs = 0;
 	bool ref = false;
 	const char *regs;
-	struct probe_trace_arg *tvar = pf->tvar;
 	int ret;
 
 	if (dwarf_attr(vr_die, DW_AT_external, &attr) != NULL)
@@ -411,16 +478,16 @@ static int convert_variable_location(Dwarf_Die *vr_die, struct probe_finder *pf)
 
 	/* TODO: handle more than 1 exprs */
 	if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL ||
-	    dwarf_getlocation_addr(&attr, pf->addr, &op, &nops, 1) <= 0 ||
+	    dwarf_getlocation_addr(&attr, addr, &op, &nops, 1) <= 0 ||
 	    nops == 0) {
 		/* TODO: Support const_value */
-		pr_err("Failed to find the location of %s at this address.\n"
-		       " Perhaps, it has been optimized out.\n", pf->pvar->var);
 		return -ENOENT;
 	}
 
 	if (op->atom == DW_OP_addr) {
 static_var:
+		if (!tvar)
+			return 0;
 		/* Static variables on memory (not stack), make @varname */
 		ret = strlen(dwarf_diename(vr_die));
 		tvar->value = zalloc(ret + 2);
@@ -435,14 +502,11 @@ static_var:
 
 	/* If this is based on frame buffer, set the offset */
 	if (op->atom == DW_OP_fbreg) {
-		if (pf->fb_ops == NULL) {
-			pr_warning("The attribute of frame base is not "
-				   "supported.\n");
+		if (fb_ops == NULL)
 			return -ENOTSUP;
-		}
 		ref = true;
 		offs = op->number;
-		op = &pf->fb_ops[0];
+		op = &fb_ops[0];
 	}
 
 	if (op->atom >= DW_OP_breg0 && op->atom <= DW_OP_breg31) {
@@ -458,13 +522,18 @@ static_var:
 	} else if (op->atom == DW_OP_regx) {
 		regn = op->number;
 	} else {
-		pr_warning("DW_OP %x is not supported.\n", op->atom);
+		pr_debug("DW_OP %x is not supported.\n", op->atom);
 		return -ENOTSUP;
 	}
 
+	if (!tvar)
+		return 0;
+
 	regs = get_arch_regstr(regn);
 	if (!regs) {
-		pr_warning("Mapping for DWARF register number %u missing on this architecture.", regn);
+		/* This should be a bug in DWARF or this tool */
+		pr_warning("Mapping for DWARF register number %u "
+			   "missing on this architecture.", regn);
 		return -ERANGE;
 	}
 
@@ -689,8 +758,14 @@ static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
 	pr_debug("Converting variable %s into trace event.\n",
 		 dwarf_diename(vr_die));
 
-	ret = convert_variable_location(vr_die, pf);
-	if (ret == 0 && pf->pvar->field) {
+	ret = convert_variable_location(vr_die, pf->addr, pf->fb_ops,
+					pf->tvar);
+	if (ret == -ENOENT)
+		pr_err("Failed to find the location of %s at this address.\n"
+		       " Perhaps, it has been optimized out.\n", pf->pvar->var);
+	else if (ret == -ENOTSUP)
+		pr_err("Sorry, we don't support this variable location yet.\n");
+	else if (pf->pvar->field) {
 		ret = convert_variable_fields(vr_die, pf->pvar->var,
 					      pf->pvar->field, &pf->tvar->ref,
 					      &die_mem);
@@ -772,34 +847,12 @@ found:
 	return ret;
 }
 
-/* Show a probe point to output buffer */
-static int convert_probe_point(Dwarf_Die *sp_die, struct probe_finder *pf)
+/* Convert subprogram DIE to trace point */
+static int convert_to_trace_point(Dwarf_Die *sp_die, Dwarf_Addr paddr,
+				  bool retprobe, struct probe_trace_point *tp)
 {
-	struct probe_trace_event *tev;
 	Dwarf_Addr eaddr;
-	Dwarf_Die die_mem;
 	const char *name;
-	int ret, i;
-	Dwarf_Attribute fb_attr;
-	size_t nops;
-
-	if (pf->ntevs == pf->max_tevs) {
-		pr_warning("Too many( > %d) probe point found.\n",
-			   pf->max_tevs);
-		return -ERANGE;
-	}
-	tev = &pf->tevs[pf->ntevs++];
-
-	/* If no real subprogram, find a real one */
-	if (!sp_die || dwarf_tag(sp_die) != DW_TAG_subprogram) {
-		sp_die = die_find_real_subprogram(&pf->cu_die,
-						 pf->addr, &die_mem);
-		if (!sp_die) {
-			pr_warning("Failed to find probe point in any "
-				   "functions.\n");
-			return -ENOENT;
-		}
-	}
 
 	/* Copy the name of probe point */
 	name = dwarf_diename(sp_die);
@@ -809,26 +862,45 @@ static int convert_probe_point(Dwarf_Die *sp_die, struct probe_finder *pf)
 				   dwarf_diename(sp_die));
 			return -ENOENT;
 		}
-		tev->point.symbol = strdup(name);
-		if (tev->point.symbol == NULL)
+		tp->symbol = strdup(name);
+		if (tp->symbol == NULL)
 			return -ENOMEM;
-		tev->point.offset = (unsigned long)(pf->addr - eaddr);
+		tp->offset = (unsigned long)(paddr - eaddr);
 	} else
 		/* This function has no name. */
-		tev->point.offset = (unsigned long)pf->addr;
+		tp->offset = (unsigned long)paddr;
 
 	/* Return probe must be on the head of a subprogram */
-	if (pf->pev->point.retprobe) {
-		if (tev->point.offset != 0) {
+	if (retprobe) {
+		if (eaddr != paddr) {
 			pr_warning("Return probe must be on the head of"
 				   " a real function\n");
 			return -EINVAL;
 		}
-		tev->point.retprobe = true;
+		tp->retprobe = true;
 	}
 
-	pr_debug("Probe point found: %s+%lu\n", tev->point.symbol,
-		 tev->point.offset);
+	return 0;
+}
+
+/* Call probe_finder callback with real subprogram DIE */
+static int call_probe_finder(Dwarf_Die *sp_die, struct probe_finder *pf)
+{
+	Dwarf_Die die_mem;
+	Dwarf_Attribute fb_attr;
+	size_t nops;
+	int ret;
+
+	/* If no real subprogram, find a real one */
+	if (!sp_die || dwarf_tag(sp_die) != DW_TAG_subprogram) {
+		sp_die = die_find_real_subprogram(&pf->cu_die,
+						  pf->addr, &die_mem);
+		if (!sp_die) {
+			pr_warning("Failed to find probe point in any "
+				   "functions.\n");
+			return -ENOENT;
+		}
+	}
 
 	/* Get the frame base attribute/ops */
 	dwarf_attr(sp_die, DW_AT_frame_base, &fb_attr);
@@ -848,22 +920,13 @@ static int convert_probe_point(Dwarf_Die *sp_die, struct probe_finder *pf)
 #endif
 	}
 
-	/* Find each argument */
-	tev->nargs = pf->pev->nargs;
-	tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
-	if (tev->args == NULL)
-		return -ENOMEM;
-	for (i = 0; i < pf->pev->nargs; i++) {
-		pf->pvar = &pf->pev->args[i];
-		pf->tvar = &tev->args[i];
-		ret = find_variable(sp_die, pf);
-		if (ret != 0)
-			return ret;
-	}
+	/* Call finder's callback handler */
+	ret = pf->callback(sp_die, pf);
 
 	/* *pf->fb_ops will be cached in libdw. Don't free it. */
 	pf->fb_ops = NULL;
-	return 0;
+
+	return ret;
 }
 
 /* Find probe point from its line number */
@@ -899,7 +962,7 @@ static int find_probe_point_by_line(struct probe_finder *pf)
 			 (int)i, lineno, (uintmax_t)addr);
 		pf->addr = addr;
 
-		ret = convert_probe_point(NULL, pf);
+		ret = call_probe_finder(NULL, pf);
 		/* Continuing, because target line might be inlined. */
 	}
 	return ret;
@@ -1012,7 +1075,7 @@ static int find_probe_point_lazy(Dwarf_Die *sp_die, struct probe_finder *pf)
 			 (int)i, lineno, (unsigned long long)addr);
 		pf->addr = addr;
 
-		ret = convert_probe_point(sp_die, pf);
+		ret = call_probe_finder(sp_die, pf);
 		/* Continuing, because target line might be inlined. */
 	}
 	/* TODO: deallocate lines, but how? */
@@ -1047,7 +1110,7 @@ static int probe_point_inline_cb(Dwarf_Die *in_die, void *data)
 		pr_debug("found inline addr: 0x%jx\n",
 			 (uintmax_t)pf->addr);
 
-		param->retval = convert_probe_point(in_die, pf);
+		param->retval = call_probe_finder(in_die, pf);
 		if (param->retval < 0)
 			return DWARF_CB_ABORT;
 	}
@@ -1085,7 +1148,7 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data)
 			}
 			pf->addr += pp->offset;
 			/* TODO: Check the address in this function */
-			param->retval = convert_probe_point(sp_die, pf);
+			param->retval = call_probe_finder(sp_die, pf);
 		}
 	} else {
 		struct dwarf_callback_param _param = {.data = (void *)pf,
@@ -1107,70 +1170,229 @@ static int find_probe_point_by_func(struct probe_finder *pf)
 	return _param.retval;
 }
 
-/* Find probe_trace_events specified by perf_probe_event from debuginfo */
-int find_probe_trace_events(int fd, struct perf_probe_event *pev,
-			     struct probe_trace_event **tevs, int max_tevs)
+/* Find probe points from debuginfo */
+static int find_probes(int fd, struct probe_finder *pf)
 {
-	struct probe_finder pf = {.pev = pev, .max_tevs = max_tevs};
-	struct perf_probe_point *pp = &pev->point;
+	struct perf_probe_point *pp = &pf->pev->point;
 	Dwarf_Off off, noff;
 	size_t cuhl;
 	Dwarf_Die *diep;
 	Dwarf *dbg;
 	int ret = 0;
 
-	pf.tevs = zalloc(sizeof(struct probe_trace_event) * max_tevs);
-	if (pf.tevs == NULL)
-		return -ENOMEM;
-	*tevs = pf.tevs;
-	pf.ntevs = 0;
-
 	dbg = dwarf_begin(fd, DWARF_C_READ);
 	if (!dbg) {
 		pr_warning("No dwarf info found in the vmlinux - "
 			"please rebuild with CONFIG_DEBUG_INFO=y.\n");
-		free(pf.tevs);
-		*tevs = NULL;
 		return -EBADF;
 	}
 
 #if _ELFUTILS_PREREQ(0, 142)
 	/* Get the call frame information from this dwarf */
-	pf.cfi = dwarf_getcfi(dbg);
+	pf->cfi = dwarf_getcfi(dbg);
 #endif
 
 	off = 0;
-	line_list__init(&pf.lcache);
+	line_list__init(&pf->lcache);
 	/* Loop on CUs (Compilation Unit) */
 	while (!dwarf_nextcu(dbg, off, &noff, &cuhl, NULL, NULL, NULL) &&
 	       ret >= 0) {
 		/* Get the DIE(Debugging Information Entry) of this CU */
-		diep = dwarf_offdie(dbg, off + cuhl, &pf.cu_die);
+		diep = dwarf_offdie(dbg, off + cuhl, &pf->cu_die);
 		if (!diep)
 			continue;
 
 		/* Check if target file is included. */
 		if (pp->file)
-			pf.fname = cu_find_realpath(&pf.cu_die, pp->file);
+			pf->fname = cu_find_realpath(&pf->cu_die, pp->file);
 		else
-			pf.fname = NULL;
+			pf->fname = NULL;
 
-		if (!pp->file || pf.fname) {
+		if (!pp->file || pf->fname) {
 			if (pp->function)
-				ret = find_probe_point_by_func(&pf);
+				ret = find_probe_point_by_func(pf);
 			else if (pp->lazy_line)
-				ret = find_probe_point_lazy(NULL, &pf);
+				ret = find_probe_point_lazy(NULL, pf);
 			else {
-				pf.lno = pp->line;
-				ret = find_probe_point_by_line(&pf);
+				pf->lno = pp->line;
+				ret = find_probe_point_by_line(pf);
 			}
 		}
 		off = noff;
 	}
-	line_list__free(&pf.lcache);
+	line_list__free(&pf->lcache);
 	dwarf_end(dbg);
 
-	return (ret < 0) ? ret : pf.ntevs;
+	return ret;
+}
+
+/* Add a found probe point into trace event list */
+static int add_probe_trace_event(Dwarf_Die *sp_die, struct probe_finder *pf)
+{
+	struct trace_event_finder *tf =
+			container_of(pf, struct trace_event_finder, pf);
+	struct probe_trace_event *tev;
+	int ret, i;
+
+	/* Check number of tevs */
+	if (tf->ntevs == tf->max_tevs) {
+		pr_warning("Too many( > %d) probe point found.\n",
+			   tf->max_tevs);
+		return -ERANGE;
+	}
+	tev = &tf->tevs[tf->ntevs++];
+
+	ret = convert_to_trace_point(sp_die, pf->addr, pf->pev->point.retprobe,
+				     &tev->point);
+	if (ret < 0)
+		return ret;
+
+	pr_debug("Probe point found: %s+%lu\n", tev->point.symbol,
+		 tev->point.offset);
+
+	/* Find each argument */
+	tev->nargs = pf->pev->nargs;
+	tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
+	if (tev->args == NULL)
+		return -ENOMEM;
+	for (i = 0; i < pf->pev->nargs; i++) {
+		pf->pvar = &pf->pev->args[i];
+		pf->tvar = &tev->args[i];
+		ret = find_variable(sp_die, pf);
+		if (ret != 0)
+			return ret;
+	}
+
+	return 0;
+}
+
+/* Find probe_trace_events specified by perf_probe_event from debuginfo */
+int find_probe_trace_events(int fd, struct perf_probe_event *pev,
+			    struct probe_trace_event **tevs, int max_tevs)
+{
+	struct trace_event_finder tf = {
+			.pf = {.pev = pev, .callback = add_probe_trace_event},
+			.max_tevs = max_tevs};
+	int ret;
+
+	/* Allocate result tevs array */
+	*tevs = zalloc(sizeof(struct probe_trace_event) * max_tevs);
+	if (*tevs == NULL)
+		return -ENOMEM;
+
+	tf.tevs = *tevs;
+	tf.ntevs = 0;
+
+	ret = find_probes(fd, &tf.pf);
+	if (ret < 0) {
+		free(*tevs);
+		*tevs = NULL;
+		return ret;
+	}
+
+	return (ret < 0) ? ret : tf.ntevs;
+}
+
+#define MAX_VAR_LEN 64
+
+/* Collect available variables in this scope */
+static int collect_variables_cb(Dwarf_Die *die_mem, void *data)
+{
+	struct available_var_finder *af = data;
+	struct variable_list *vl;
+	char buf[MAX_VAR_LEN];
+	int tag, ret;
+
+	vl = &af->vls[af->nvls - 1];
+
+	tag = dwarf_tag(die_mem);
+	if (tag == DW_TAG_formal_parameter ||
+	    tag == DW_TAG_variable) {
+		ret = convert_variable_location(die_mem, af->pf.addr,
+						af->pf.fb_ops, NULL);
+		if (ret == 0) {
+			ret = die_get_varname(die_mem, buf, MAX_VAR_LEN);
+			if (ret > 0)
+				strlist__add(vl->vars, buf);
+		}
+	}
+
+	if (dwarf_haspc(die_mem, af->pf.addr))
+		return DIE_FIND_CB_CONTINUE;
+	else
+		return DIE_FIND_CB_SIBLING;
+}
+
+/* Add a found vars into available variables list */
+static int add_available_vars(Dwarf_Die *sp_die, struct probe_finder *pf)
+{
+	struct available_var_finder *af =
+			container_of(pf, struct available_var_finder, pf);
+	struct variable_list *vl;
+	Dwarf_Die die_mem;
+	int ret;
+
+	/* Check number of tevs */
+	if (af->nvls == af->max_vls) {
+		pr_warning("Too many( > %d) probe point found.\n", af->max_vls);
+		return -ERANGE;
+	}
+	vl = &af->vls[af->nvls++];
+
+	ret = convert_to_trace_point(sp_die, pf->addr, pf->pev->point.retprobe,
+				     &vl->point);
+	if (ret < 0)
+		return ret;
+
+	pr_debug("Probe point found: %s+%lu\n", vl->point.symbol,
+		 vl->point.offset);
+
+	/* Find local variables */
+	vl->vars = strlist__new(true, NULL);
+	if (vl->vars == NULL)
+		return -ENOMEM;
+	die_find_child(sp_die, collect_variables_cb, (void *)af, &die_mem);
+
+	if (strlist__empty(vl->vars)) {
+		strlist__delete(vl->vars);
+		vl->vars = NULL;
+	}
+
+	return ret;
+}
+
+/* Find available variables at given probe point */
+int find_available_vars_at(int fd, struct perf_probe_event *pev,
+			   struct variable_list **vls, int max_vls)
+{
+	struct available_var_finder af = {
+			.pf = {.pev = pev, .callback = add_available_vars},
+			.max_vls = max_vls};
+	int ret;
+
+	/* Allocate result vls array */
+	*vls = zalloc(sizeof(struct variable_list) * max_vls);
+	if (*vls == NULL)
+		return -ENOMEM;
+
+	af.vls = *vls;
+	af.nvls = 0;
+
+	ret = find_probes(fd, &af.pf);
+	if (ret < 0) {
+		/* Free vlist for error */
+		while (af.nvls--) {
+			if (af.vls[af.nvls].point.symbol)
+				free(af.vls[af.nvls].point.symbol);
+			if (af.vls[af.nvls].vars)
+				strlist__delete(af.vls[af.nvls].vars);
+		}
+		free(af.vls);
+		*vls = NULL;
+		return ret;
+	}
+
+	return (ret < 0) ? ret : af.nvls;
 }
 
 /* Reverse search */