perf probe: Fix to avoid crashing if DW_AT_decl_file is NULL

Since clang generates DWARF5 which sets DW_AT_decl_file as 0,
dwarf_decl_file() thinks that is invalid and returns NULL.  In that case
'perf probe' SIGSEGVs because it doesn't expect a NULL decl_file.

This adds a dwarf_decl_file() return value check to avoid such SEGV with
clang generated DWARF5 info.

Without this, 'perf probe' crashes:

  $ perf probe -k $BIN_PATH/vmlinux -s $SRC_PATH -L vfs_read:10
  Segmentation fault
  $

With this, it just warns about it:

  $ perf probe -k $BIN_PATH/vmlinux -s $SRC_PATH -L vfs_read:10
  Debuginfo analysis failed.
    Error: Failed to show lines.
  $

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/166731051077.2100653.15626653369345128302.stgit@devnote3
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/dwarf-aux.c

@@ -137,7 +137,7 @@ int cu_find_lineinfo(Dwarf_Die *cu_die, Dwarf_Addr addr,
 	}
 
 out:
-	return *lineno ?: -ENOENT;
+	return (*lineno && *fname) ? *lineno : -ENOENT;
 }
 
 static int __die_find_inline_cb(Dwarf_Die *die_mem, void *data);
@@ -874,6 +874,11 @@ int die_walk_lines(Dwarf_Die *rt_die, line_walk_callback_t callback, void *data)
 		cu_die = dwarf_diecu(rt_die, &die_mem, NULL, NULL);
 		dwarf_decl_line(rt_die, &decl);
 		decf = dwarf_decl_file(rt_die);
+		if (!decf) {
+			pr_debug2("Failed to get the declared file name of %s\n",
+				  dwarf_diename(rt_die));
+			return -EINVAL;
+		}
 	} else
 		cu_die = rt_die;
 	if (!cu_die) {

tools/perf/util/probe-finder.c

@@ -1063,6 +1063,7 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data)
 	struct dwarf_callback_param *param = data;
 	struct probe_finder *pf = param->data;
 	struct perf_probe_point *pp = &pf->pev->point;
+	const char *fname;
 
 	/* Check tag and diename */
 	if (!die_is_func_def(sp_die) ||
@@ -1070,12 +1071,17 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data)
 		return DWARF_CB_OK;
 
 	/* Check declared file */
-	if (pp->file && strtailcmp(pp->file, dwarf_decl_file(sp_die)))
+	fname = dwarf_decl_file(sp_die);
+	if (!fname) {
+		pr_warning("A function DIE doesn't have decl_line. Maybe broken DWARF?\n");
+		return DWARF_CB_OK;
+	}
+	if (pp->file && fname && strtailcmp(pp->file, fname))
 		return DWARF_CB_OK;
 
 	pr_debug("Matched function: %s [%lx]\n", dwarf_diename(sp_die),
 		 (unsigned long)dwarf_dieoffset(sp_die));
-	pf->fname = dwarf_decl_file(sp_die);
+	pf->fname = fname;
 	if (pp->line) { /* Function relative line */
 		dwarf_decl_line(sp_die, &pf->lno);
 		pf->lno += pp->line;
@@ -1134,6 +1140,7 @@ struct pubname_callback_param {
 static int pubname_search_cb(Dwarf *dbg, Dwarf_Global *gl, void *data)
 {
 	struct pubname_callback_param *param = data;
+	const char *fname;
 
 	if (dwarf_offdie(dbg, gl->die_offset, param->sp_die)) {
 		if (dwarf_tag(param->sp_die) != DW_TAG_subprogram)
@@ -1143,9 +1150,11 @@ static int pubname_search_cb(Dwarf *dbg, Dwarf_Global *gl, void *data)
 			if (!dwarf_offdie(dbg, gl->cu_offset, param->cu_die))
 				return DWARF_CB_OK;
 
-			if (param->file &&
-			    strtailcmp(param->file, dwarf_decl_file(param->sp_die)))
-				return DWARF_CB_OK;
+			if (param->file) {
+				fname = dwarf_decl_file(param->sp_die);
+				if (!fname || strtailcmp(param->file, fname))
+					return DWARF_CB_OK;
+			}
 
 			param->found = 1;
 			return DWARF_CB_ABORT;
@@ -1779,7 +1788,7 @@ int debuginfo__find_probe_point(struct debuginfo *dbg, u64 addr,
 		}
 		/* Verify the lineno and baseline are in a same file */
 		tmp = dwarf_decl_file(&spdie);
-		if (!tmp || strcmp(tmp, fname) != 0)
+		if (!tmp || (fname && strcmp(tmp, fname) != 0))
 			lineno = 0;
 	}
 
@@ -1889,10 +1898,14 @@ static int line_range_search_cb(Dwarf_Die *sp_die, void *data)
 	struct dwarf_callback_param *param = data;
 	struct line_finder *lf = param->data;
 	struct line_range *lr = lf->lr;
+	const char *fname;
 
 	/* Check declared file */
-	if (lr->file && strtailcmp(lr->file, dwarf_decl_file(sp_die)))
-		return DWARF_CB_OK;
+	if (lr->file) {
+		fname = dwarf_decl_file(sp_die);
+		if (!fname || strtailcmp(lr->file, fname))
+			return DWARF_CB_OK;
+	}
 
 	if (die_match_name(sp_die, lr->function) && die_is_func_def(sp_die)) {
 		lf->fname = dwarf_decl_file(sp_die);