linux-kernel - [PATCH v1 11/11] perf dwarf-aux: Collect all variable locations for insn tracking

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Message-ID: <20260127020617.2804780-12-zli94@ncsu.edu>
Date: Mon, 26 Jan 2026 21:05:04 -0500
From: Zecheng Li <zli94@...u.edu>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	Zecheng Li <zli94@...u.edu>,
	xliuprof@...gle.com,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v1 11/11] 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@...u.edu>
---
 tools/perf/util/dwarf-aux.c | 60 ++++++++++++++++++-------------------
 1 file changed, 30 insertions(+), 30 deletions(-)

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index a05d73d6e9e7..3a028d4acb78 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1643,6 +1643,7 @@ 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;
@@ -1650,41 +1651,40 @@ 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;
 }
-- 
2.52.0