Subject: [PATCH V3 13/14] tools/perf: Add support for global_die to capture name of variable in case of register defined variable

From: Athira Rajeev <[email-masked]>
Date: Sat, 1 Jun 2024 11:39:40 +0530

In case of register defined variable (found using
find_data_type_global_reg), if the type of variable happens to be base
type (example, long unsigned int), perf report captures it as:

    12.85%  long unsigned int  long unsigned int +0 (no field)

The above data type is actually referring to samples captured while
accessing "r1" which represents current stack pointer in powerpc.
register void *__stack_pointer asm("r1");

The dwarf debug contains this as:

<<>>
 <1><18dd772>: Abbrev Number: 129 (DW_TAG_variable)
    <18dd774>   DW_AT_name        : (indirect string, offset: 0x11ba): current_stack_pointer
    <18dd778>   DW_AT_decl_file   : 51
    <18dd779>   DW_AT_decl_line   : 1468
    <18dd77b>   DW_AT_decl_column : 24
    <18dd77c>   DW_AT_type        : <0x18da5cd>
    <18dd780>   DW_AT_external    : 1
    <18dd780>   DW_AT_location    : 1 byte block: 51    (DW_OP_reg1 (r1))

 where 18da5cd is:

 <1><18da5cd>: Abbrev Number: 47 (DW_TAG_base_type)
    <18da5ce>   DW_AT_byte_size   : 8
    <18da5cf>   DW_AT_encoding    : 7   (unsigned)
    <18da5d0>   DW_AT_name        : (indirect string, offset: 0x55c7): long unsigned int
<<>>

To make it more clear to the user, capture the DW_AT_name of the
variable and save it as part of Dwarf_Global. Dwarf_Global is used so
that it can be used and retrieved while presenting the result.

Update "dso__findnew_data_type" function to set "var_name" if
variable name is set as part of Dwarf_Global. Updated
"hist_entry__typeoff_snprintf" to print var_name if it is set.
With the changes, along with "long unsigned int" report also says the
variable name as current_stack_pointer

Snippet of result:

    12.85%  long unsigned int  long unsigned int +0 (current_stack_pointer)
     4.68%  struct paca_struct  struct paca_struct +2312 (__current)
     4.57%  struct paca_struct  struct paca_struct +2354 (irq_soft_mask)

Signed-off-by: Athira Rajeev <[email-masked]>
---
 tools/perf/util/annotate-data.c | 30 ++++++++++++++++++++++++------
 tools/perf/util/dwarf-aux.c     |  1 +
 tools/perf/util/dwarf-aux.h     |  1 +
 tools/perf/util/sort.c          |  7 +++++--
 4 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 82232f2d8e16..2bce522304f4 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -268,23 +268,32 @@ static void delete_members(struct annotated_member *member)
 }
 
 static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
-							  Dwarf_Die *type_die)
+							  Dwarf_Die *type_die, Dwarf_Global *global_die)
 {
 	struct annotated_data_type *result = NULL;
 	struct annotated_data_type key;
 	struct rb_node *node;
 	struct strbuf sb;
+	struct strbuf sb_var_name;
 	char *type_name;
+	char *var_name;
 	Dwarf_Word size;
 
 	strbuf_init(&sb, 32);
+	strbuf_init(&sb_var_name, 32);
 	if (die_get_typename_from_type(type_die, &sb) < 0)
 		strbuf_add(&sb, "(unknown type)", 14);
+	if (global_die->name) {
+		strbuf_addstr(&sb_var_name, global_die->name);
+		var_name = strbuf_detach(&sb_var_name, NULL);
+	}
 	type_name = strbuf_detach(&sb, NULL);
 	dwarf_aggregate_size(type_die, &size);
 
 	/* Check existing nodes in dso->data_types tree */
 	key.self.type_name = type_name;
+	if (global_die->name)
+		key.self.var_name = var_name;
 	key.self.size = size;
 	node = rb_find(&key, dso__data_types(dso), data_type_cmp);
 	if (node) {
@@ -301,6 +310,8 @@ static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
 	}
 
 	result->self.type_name = type_name;
+	if (global_die->name)
+		result->self.var_name = var_name;
 	result->self.size = size;
 	INIT_LIST_HEAD(&result->self.children);
 
@@ -1178,7 +1189,7 @@ static int find_data_type_block(struct data_loc_info *dloc,
  * cu_die and match with reg to identify data type die.
  */
 static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_Die *cu_die,
-		Dwarf_Die *type_die)
+		Dwarf_Die *type_die, Dwarf_Global *global_die)
 {
 	Dwarf_Die vr_die;
 	int ret = -1;
@@ -1190,8 +1201,11 @@ static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_
 			if (dwarf_offdie(dloc->di->dbg, var_types->die_off, &vr_die)) {
 				if (die_get_real_type(&vr_die, type_die) == NULL) {
 					dloc->type_offset = 0;
+					global_die->name = var_types->name;
 					dwarf_offdie(dloc->di->dbg, var_types->die_off, type_die);
 				}
+				global_die->die_offset = (long)dwarf_dieoffset(type_die);
+				global_die->cu_offset = (long)dwarf_dieoffset(cu_die);
 				pr_debug_type_name(type_die, TSR_KIND_TYPE);
 				ret = 0;
 				pr_debug_dtp("found by CU for %s (die:%#lx)\n",
@@ -1205,7 +1219,8 @@ static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_
 }
 
 /* The result will be saved in @type_die */
-static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
+static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die,
+		Dwarf_Global *global_die)
 {
 	struct annotated_op_loc *loc = dloc->op;
 	Dwarf_Die cu_die, var_die;
@@ -1219,6 +1234,8 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
 	u64 pc;
 	char buf[64];
 
+	memset(global_die, 0, sizeof(Dwarf_Global));
+
 	if (dloc->op->multi_regs)
 		snprintf(buf, sizeof(buf), "reg%d, reg%d", dloc->op->reg1, dloc->op->reg2);
 	else if (dloc->op->reg1 == DWARF_REG_PC)
@@ -1252,7 +1269,7 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
 		     dwarf_diename(&cu_die), (long)dwarf_dieoffset(&cu_die));
 
 	if (loc->reg_type == DWARF_REG_GLOBAL) {
-		ret = find_data_type_global_reg(dloc, reg, &cu_die, type_die);
+		ret = find_data_type_global_reg(dloc, reg, &cu_die, type_die, global_die);
 		if (!ret)
 			goto out;
 	}
@@ -1388,6 +1405,7 @@ struct annotated_data_type *find_data_type(struct data_loc_info *dloc)
 	struct annotated_data_type *result = NULL;
 	struct dso *dso = map__dso(dloc->ms->map);
 	Dwarf_Die type_die;
+	Dwarf_Global global_die;
 
 	dloc->di = debuginfo__new(dso__long_name(dso));
 	if (dloc->di == NULL) {
@@ -1403,10 +1421,10 @@ struct annotated_data_type *find_data_type(struct data_loc_info *dloc)
 
 	dloc->fbreg = -1;
 
-	if (find_data_type_die(dloc, &type_die) < 0)
+	if (find_data_type_die(dloc, &type_die, &global_die) < 0)
 		goto out;
 
-	result = dso__findnew_data_type(dso, &type_die);
+	result = dso__findnew_data_type(dso, &type_die, &global_die);
 
 out:
 	debuginfo__delete(dloc->di);
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 44ef968a7ad3..9e61ff326651 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1610,6 +1610,7 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
 	vt->reg = reg_from_dwarf_op(ops);
 	vt->offset = offset_from_dwarf_op(ops);
 	vt->next = *var_types;
+	vt->name = dwarf_diename(die_mem);
 	*var_types = vt;
 
 	return DIE_FIND_CB_SIBLING;
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index 24446412b869..406a5b1e269b 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -146,6 +146,7 @@ struct die_var_type {
 	u64 addr;
 	int reg;
 	int offset;
+	const char *name;
 };
 
 /* Return type info of a member at offset */
diff --git a/tools/perf/util/sort.c b/tools/perf/util/sort.c
index cd39ea972193..535ca19a23fd 100644
--- a/tools/perf/util/sort.c
+++ b/tools/perf/util/sort.c
@@ -2305,9 +2305,12 @@ static int hist_entry__typeoff_snprintf(struct hist_entry *he, char *bf,
 	char buf[4096];
 
 	buf[0] = '\0';
-	if (list_empty(&he_type->self.children))
+	if (list_empty(&he_type->self.children)) {
 		snprintf(buf, sizeof(buf), "no field");
-	else
+		if (he_type->self.var_name)
+			strcpy(buf, he_type->self.var_name);
+
+	} else
 		fill_member_name(buf, sizeof(buf), &he_type->self,
 				 he->mem_type_off, true);
 	buf[4095] = '\0';
-- 
2.43.0