perf probe: Support comp_dir to find an absolute source path

index 8d08e75..4445a1e 100644
@@ -201,28 +201,38 @@ static int try_to_find_kprobe_trace_events(struct perf_probe_event *pev,
  * a newly allocated path on success.
  * Return 0 if file was found and readable, -errno otherwise.
  */
-static int get_real_path(const char *raw_path, char **new_path)
+static int get_real_path(const char *raw_path, const char *comp_dir,
+			 char **new_path)
 {
-	if (!symbol_conf.source_prefix) {
-		if (access(raw_path, R_OK) == 0) {
-			*new_path = strdup(raw_path);
-			return 0;
-		} else
-			return -errno;
+	const char *prefix = symbol_conf.source_prefix;
+
+	if (!prefix) {
+		if (raw_path[0] != '/' && comp_dir)
+			/* If not an absolute path, try to use comp_dir */
+			prefix = comp_dir;
+		else {
+			if (access(raw_path, R_OK) == 0) {
+				*new_path = strdup(raw_path);
+				return 0;
+			} else
+				return -errno;
+		}
 	}
 
-	*new_path = malloc((strlen(symbol_conf.source_prefix) +
-			    strlen(raw_path) + 2));
+	*new_path = malloc((strlen(prefix) + strlen(raw_path) + 2));
 	if (!*new_path)
 		return -ENOMEM;
 
 	for (;;) {
-		sprintf(*new_path, "%s/%s", symbol_conf.source_prefix,
-			raw_path);
+		sprintf(*new_path, "%s/%s", prefix, raw_path);
 
 		if (access(*new_path, R_OK) == 0)
 			return 0;
 
+		if (!symbol_conf.source_prefix)
+			/* In case of searching comp_dir, don't retry */
+			return -errno;
+
 		switch (errno) {
 		case ENAMETOOLONG:
 		case ENOENT:

@@ -318,7 +328,7 @@ int show_line_range(struct line_range *lr)
 
 	/* Convert source file path */
 	tmp = lr->path;
-	ret = get_real_path(tmp, &lr->path);
+	ret = get_real_path(tmp, lr->comp_dir, &lr->path);
 	free(tmp);	/* Free old path */
 	if (ret < 0) {
 		pr_warning("Failed to find source file. (%d)\n", ret);

index bc06d3e..ed362ac 100644
@@ -86,6 +86,7 @@ struct line_range {
 	int			end;		/* End line number */
 	int			offset;		/* Start line offset */
 	char			*path;		/* Real path name */
+	char			*comp_dir;	/* Compile directory */
 	struct list_head	line_list;	/* Visible lines */
 };
 

index a934a36..37dcdb6 100644
@@ -144,6 +144,15 @@ static const char *cu_find_realpath(Dwarf_Die *cu_die, const char *fname)
 	return src;
 }
 
+/* Get DW_AT_comp_dir (should be NULL with older gcc) */
+static const char *cu_get_comp_dir(Dwarf_Die *cu_die)
+{
+	Dwarf_Attribute attr;
+	if (dwarf_attr(cu_die, DW_AT_comp_dir, &attr) == NULL)
+		return NULL;
+	return dwarf_formstring(&attr);
+}
+
 /* Compare diename and tname */
 static bool die_compare_name(Dwarf_Die *dw_die, const char *tname)
 {

@@ -1374,6 +1383,7 @@ int find_line_range(int fd, struct line_range *lr)
 	size_t cuhl;
 	Dwarf_Die *diep;
 	Dwarf *dbg;
+	const char *comp_dir;
 
 	dbg = dwarf_begin(fd, DWARF_C_READ);
 	if (!dbg) {

@@ -1409,6 +1419,17 @@ int find_line_range(int fd, struct line_range *lr)
 		}
 		off = noff;
 	}
+
+	/* Store comp_dir */
+	if (lf.found) {
+		comp_dir = cu_get_comp_dir(&lf.cu_die);
+		if (comp_dir) {
+			lr->comp_dir = strdup(comp_dir);
+			if (!lr->comp_dir)
+				ret = -ENOMEM;
+		}
+	}
+
 	pr_debug("path: %s\n", lr->path);
 	dwarf_end(dbg);
 

index 8d08e75..4445a1e 100644
@@ -201,28 +201,38 @@ static int try_to_find_kprobe_trace_events(struct perf_probe_event *pev,
  * a newly allocated path on success.
  * Return 0 if file was found and readable, -errno otherwise.
  */
-static int get_real_path(const char *raw_path, char **new_path)
+static int get_real_path(const char *raw_path, const char *comp_dir,
+			 char **new_path)
 {
-	if (!symbol_conf.source_prefix) {
-		if (access(raw_path, R_OK) == 0) {
-			*new_path = strdup(raw_path);
-			return 0;
-		} else
-			return -errno;
+	const char *prefix = symbol_conf.source_prefix;
+
+	if (!prefix) {
+		if (raw_path[0] != '/' && comp_dir)
+			/* If not an absolute path, try to use comp_dir */
+			prefix = comp_dir;
+		else {
+			if (access(raw_path, R_OK) == 0) {
+				*new_path = strdup(raw_path);
+				return 0;
+			} else
+				return -errno;
+		}
 	}
 
-	*new_path = malloc((strlen(symbol_conf.source_prefix) +
-			    strlen(raw_path) + 2));
+	*new_path = malloc((strlen(prefix) + strlen(raw_path) + 2));
 	if (!*new_path)
 		return -ENOMEM;
 
 	for (;;) {
-		sprintf(*new_path, "%s/%s", symbol_conf.source_prefix,
-			raw_path);
+		sprintf(*new_path, "%s/%s", prefix, raw_path);
 
 		if (access(*new_path, R_OK) == 0)
 			return 0;
 
+		if (!symbol_conf.source_prefix)
+			/* In case of searching comp_dir, don't retry */
+			return -errno;
+
 		switch (errno) {
 		case ENAMETOOLONG:
 		case ENOENT:

@@ -318,7 +328,7 @@ int show_line_range(struct line_range *lr)
 
 	/* Convert source file path */
 	tmp = lr->path;
-	ret = get_real_path(tmp, &lr->path);
+	ret = get_real_path(tmp, lr->comp_dir, &lr->path);
 	free(tmp);	/* Free old path */
 	if (ret < 0) {
 		pr_warning("Failed to find source file. (%d)\n", ret);

index bc06d3e..ed362ac 100644
@@ -86,6 +86,7 @@ struct line_range {
 	int			end;		/* End line number */
 	int			offset;		/* Start line offset */
 	char			*path;		/* Real path name */
+	char			*comp_dir;	/* Compile directory */
 	struct list_head	line_list;	/* Visible lines */
 };
 

index a934a36..37dcdb6 100644
@@ -144,6 +144,15 @@ static const char *cu_find_realpath(Dwarf_Die *cu_die, const char *fname)
 	return src;
 }
 
+/* Get DW_AT_comp_dir (should be NULL with older gcc) */
+static const char *cu_get_comp_dir(Dwarf_Die *cu_die)
+{
+	Dwarf_Attribute attr;
+	if (dwarf_attr(cu_die, DW_AT_comp_dir, &attr) == NULL)
+		return NULL;
+	return dwarf_formstring(&attr);
+}
+
 /* Compare diename and tname */
 static bool die_compare_name(Dwarf_Die *dw_die, const char *tname)
 {

@@ -1374,6 +1383,7 @@ int find_line_range(int fd, struct line_range *lr)
 	size_t cuhl;
 	Dwarf_Die *diep;
 	Dwarf *dbg;
+	const char *comp_dir;
 
 	dbg = dwarf_begin(fd, DWARF_C_READ);
 	if (!dbg) {

@@ -1409,6 +1419,17 @@ int find_line_range(int fd, struct line_range *lr)
 		}
 		off = noff;
 	}
+
+	/* Store comp_dir */
+	if (lf.found) {
+		comp_dir = cu_get_comp_dir(&lf.cu_die);
+		if (comp_dir) {
+			lr->comp_dir = strdup(comp_dir);
+			if (!lr->comp_dir)
+				ret = -ENOMEM;
+		}
+	}
+
 	pr_debug("path: %s\n", lr->path);
 	dwarf_end(dbg);
 

index 37dcdb6..f88070e 100644
@@ -158,7 +158,7 @@ static bool die_compare_name(Dwarf_Die *dw_die, const char *tname)
 {
 	const char *name;
 	name = dwarf_diename(dw_die);
-	return name ? strcmp(tname, name) : -1;
+	return name ? (strcmp(tname, name) == 0) : false;
 }
 
 /* Get type die, but skip qualifiers and typedef */

@@ -329,7 +329,7 @@ static int __die_find_variable_cb(Dwarf_Die *die_mem, void *data)
 	tag = dwarf_tag(die_mem);
 	if ((tag == DW_TAG_formal_parameter ||
 	     tag == DW_TAG_variable) &&
-	    (die_compare_name(die_mem, name) == 0))
+	    die_compare_name(die_mem, name))
 		return DIE_FIND_CB_FOUND;
 
 	return DIE_FIND_CB_CONTINUE;

@@ -348,7 +348,7 @@ static int __die_find_member_cb(Dwarf_Die *die_mem, void *data)
 	const char *name = data;
 
 	if ((dwarf_tag(die_mem) == DW_TAG_member) &&
-	    (die_compare_name(die_mem, name) == 0))
+	    die_compare_name(die_mem, name))
 		return DIE_FIND_CB_FOUND;
 
 	return DIE_FIND_CB_SIBLING;

@@ -506,8 +506,8 @@ static int convert_variable_type(Dwarf_Die *vr_die,
 				return -ENOMEM;
 			}
 		}
-		if (die_compare_name(&type, "char") != 0 &&
-		    die_compare_name(&type, "unsigned char") != 0) {
+		if (!die_compare_name(&type, "char") &&
+		    !die_compare_name(&type, "unsigned char")) {
 			pr_warning("Failed to cast into string: "
 				   "%s is not (unsigned) char *.",
 				   dwarf_diename(vr_die));

@@ -1017,7 +1017,7 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data)
 
 	/* Check tag and diename */
 	if (dwarf_tag(sp_die) != DW_TAG_subprogram ||
-	    die_compare_name(sp_die, pp->function) != 0)
+	    !die_compare_name(sp_die, pp->function))
 		return DWARF_CB_OK;
 
 	pf->fname = dwarf_decl_file(sp_die);

@@ -1340,7 +1340,7 @@ static int line_range_search_cb(Dwarf_Die *sp_die, void *data)
 	struct line_range *lr = lf->lr;
 
 	if (dwarf_tag(sp_die) == DW_TAG_subprogram &&
-	    die_compare_name(sp_die, lr->function) == 0) {
+	    die_compare_name(sp_die, lr->function)) {
 		lf->fname = dwarf_decl_file(sp_die);
 		dwarf_decl_line(sp_die, &lr->offset);
 		pr_debug("fname: %s, lineno:%d\n", lf->fname, lr->offset);

index 37dcdb6..f88070e 100644
@@ -158,7 +158,7 @@ static bool die_compare_name(Dwarf_Die *dw_die, const char *tname)
 {
 	const char *name;
 	name = dwarf_diename(dw_die);
-	return name ? strcmp(tname, name) : -1;
+	return name ? (strcmp(tname, name) == 0) : false;
 }
 
 /* Get type die, but skip qualifiers and typedef */

@@ -329,7 +329,7 @@ static int __die_find_variable_cb(Dwarf_Die *die_mem, void *data)
 	tag = dwarf_tag(die_mem);
 	if ((tag == DW_TAG_formal_parameter ||
 	     tag == DW_TAG_variable) &&
-	    (die_compare_name(die_mem, name) == 0))
+	    die_compare_name(die_mem, name))
 		return DIE_FIND_CB_FOUND;
 
 	return DIE_FIND_CB_CONTINUE;

@@ -348,7 +348,7 @@ static int __die_find_member_cb(Dwarf_Die *die_mem, void *data)
 	const char *name = data;
 
 	if ((dwarf_tag(die_mem) == DW_TAG_member) &&
-	    (die_compare_name(die_mem, name) == 0))
+	    die_compare_name(die_mem, name))
 		return DIE_FIND_CB_FOUND;
 
 	return DIE_FIND_CB_SIBLING;

@@ -506,8 +506,8 @@ static int convert_variable_type(Dwarf_Die *vr_die,
 				return -ENOMEM;
 			}
 		}
-		if (die_compare_name(&type, "char") != 0 &&
-		    die_compare_name(&type, "unsigned char") != 0) {
+		if (!die_compare_name(&type, "char") &&
+		    !die_compare_name(&type, "unsigned char")) {
 			pr_warning("Failed to cast into string: "
 				   "%s is not (unsigned) char *.",
 				   dwarf_diename(vr_die));

@@ -1017,7 +1017,7 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data)
 
 	/* Check tag and diename */
 	if (dwarf_tag(sp_die) != DW_TAG_subprogram ||
-	    die_compare_name(sp_die, pp->function) != 0)
+	    !die_compare_name(sp_die, pp->function))
 		return DWARF_CB_OK;
 
 	pf->fname = dwarf_decl_file(sp_die);

@@ -1340,7 +1340,7 @@ static int line_range_search_cb(Dwarf_Die *sp_die, void *data)
 	struct line_range *lr = lf->lr;
 
 	if (dwarf_tag(sp_die) == DW_TAG_subprogram &&
-	    die_compare_name(sp_die, lr->function) == 0) {
+	    die_compare_name(sp_die, lr->function)) {
 		lf->fname = dwarf_decl_file(sp_die);
 		dwarf_decl_line(sp_die, &lr->offset);
 		pr_debug("fname: %s, lineno:%d\n", lf->fname, lr->offset);