From: Zecheng Li <zli94@ncsu.edu>
Date: Mon, 9 Mar 2026 17:55:24 +0000 (-0400)
Subject: perf dwarf-aux: Collect all variable locations for insn tracking
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a90407a5a89a29f3c4af89e55afe4d0489b8a81c;p=thirdparty%2Fkernel%2Flinux.git

perf dwarf-aux: Collect all variable locations for insn tracking

Previously, only the first DWARF location entry was collected for each
variable. This was based on the assumption that instruction tracking
could reconstruct the remaining state. However, variables may have
different locations across different address ranges, and relying solely
on instruction tracking can miss valid type information.

Change __die_collect_vars_cb() to iterate over all location entries
using dwarf_getlocations() in a loop. This ensures that variables with
multiple location ranges are properly tracked, improving type coverage.

Signed-off-by: Zecheng Li <zli94@ncsu.edu>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 0710c875416fa..92db2fccc788a 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1645,6 +1645,7 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
 	Dwarf_Op *ops;
 	size_t nops;
 	struct die_var_type *vt;
+	ptrdiff_t off;
 
 	if (tag != DW_TAG_variable && tag != DW_TAG_formal_parameter)
 		return DIE_FIND_CB_SIBLING;
@@ -1652,41 +1653,40 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
 	if (dwarf_attr(die_mem, DW_AT_location, &attr) == NULL)
 		return DIE_FIND_CB_SIBLING;
 
-	/*
-	 * Only collect the first location as it can reconstruct the
-	 * remaining state by following the instructions.
-	 * start = 0 means it covers the whole range.
-	 */
-	if (dwarf_getlocations(&attr, 0, &base, &start, &end, &ops, &nops) <= 0)
-		return DIE_FIND_CB_SIBLING;
-
-	if (!check_allowed_ops(ops, nops))
-		return DIE_FIND_CB_SIBLING;
-
 	if (__die_get_real_type(die_mem, &type_die) == NULL)
 		return DIE_FIND_CB_SIBLING;
 
-	vt = malloc(sizeof(*vt));
-	if (vt == NULL)
-		return DIE_FIND_CB_END;
-
-	/* Usually a register holds the value of a variable */
-	vt->is_reg_var_addr = false;
+	/*
+	 * Collect all location entries as variables may have different
+	 * locations across different address ranges.
+	 */
+	off = 0;
+	while ((off = dwarf_getlocations(&attr, off, &base, &start, &end, &ops, &nops)) > 0) {
+		if (!check_allowed_ops(ops, nops))
+			continue;
 
-	if (((ops->atom >= DW_OP_breg0 && ops->atom <= DW_OP_breg31) ||
-	      ops->atom == DW_OP_bregx || ops->atom == DW_OP_fbreg) &&
-	      !is_breg_access_indirect(ops, nops))
-		/* The register contains an address of the variable. */
-		vt->is_reg_var_addr = true;
+		vt = malloc(sizeof(*vt));
+		if (vt == NULL)
+			return DIE_FIND_CB_END;
 
-	vt->die_off = dwarf_dieoffset(&type_die);
-	vt->addr = start;
-	vt->end = end;
-	vt->has_range = (end != 0 || start != 0);
-	vt->reg = reg_from_dwarf_op(ops);
-	vt->offset = offset_from_dwarf_op(ops);
-	vt->next = *var_types;
-	*var_types = vt;
+		/* Usually a register holds the value of a variable */
+		vt->is_reg_var_addr = false;
+
+		if (((ops->atom >= DW_OP_breg0 && ops->atom <= DW_OP_breg31) ||
+		      ops->atom == DW_OP_bregx || ops->atom == DW_OP_fbreg) &&
+		      !is_breg_access_indirect(ops, nops))
+			/* The register contains an address of the variable. */
+			vt->is_reg_var_addr = true;
+
+		vt->die_off = dwarf_dieoffset(&type_die);
+		vt->addr = start;
+		vt->end = end;
+		vt->has_range = (end != 0 || start != 0);
+		vt->reg = reg_from_dwarf_op(ops);
+		vt->offset = offset_from_dwarf_op(ops);
+		vt->next = *var_types;
+		*var_types = vt;
+	}
 
 	return DIE_FIND_CB_SIBLING;
 }