linux-kernel - [PATCH v2 03/10] perf dwarf-aux: Better variable collection for insn tracking

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Message-ID: <20250825195412.223077-4-zecheng@google.com>
Date: Mon, 25 Aug 2025 19:54:05 +0000
From: Zecheng Li <zecheng@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	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>, 
	"Liang, Kan" <kan.liang@...ux.intel.com>, Masami Hiramatsu <mhiramat@...nel.org>
Cc: Xu Liu <xliuprof@...gle.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Zecheng Li <zecheng@...gle.com>
Subject: [PATCH v2 03/10] perf dwarf-aux: Better variable collection for insn tracking

Utilizes the previous is_breg_access_indirect function to determine if
the register + offset stores the variable itself or the struct it points
to, save the information in die_var_type.is_reg_var_addr.

Since we are storing the real types in the stack state, we need to do a
type dereference when is_reg_var_addr is set to false for stack/frame
registers.

For other gp registers, skip the variable when the register is a pointer
to the type. If we want to accept these variables, we might also utilize
is_reg_var_addr in a different way, we need to mark that register as a
pointer to the type.

Signed-off-by: Zecheng Li <zecheng@...gle.com>
---
 tools/perf/util/annotate-data.c |  9 +++++++++
 tools/perf/util/dwarf-aux.c     | 11 ++++++++++-
 tools/perf/util/dwarf-aux.h     |  2 ++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 1ef2edbc71d9..258157cc43c2 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -868,6 +868,11 @@ static void update_var_state(struct type_state *state, struct data_loc_info *dlo
 			int offset = var->offset;
 			struct type_state_stack *stack;
 
+			/* If the reg location holds the pointer value, dereference the type */
+			if (!var->is_reg_var_addr && is_pointer_type(&mem_die) &&
+				__die_get_real_type(&mem_die, &mem_die) == NULL)
+				continue;
+
 			if (var->reg != DWARF_REG_FB)
 				offset -= fb_offset;
 
@@ -893,6 +898,10 @@ static void update_var_state(struct type_state *state, struct data_loc_info *dlo
 
 			reg = &state->regs[var->reg];
 
+			/* For gp registers, skip the address registers for now */
+			if (var->is_reg_var_addr)
+				continue;
+
 			if (reg->ok && reg->kind == TSR_KIND_TYPE &&
 			    !is_better_type(&reg->type, &mem_die))
 				continue;
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 449bc9ad7aff..6fd2db5d9381 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1627,13 +1627,22 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
 	if (!check_allowed_ops(ops, nops))
 		return DIE_FIND_CB_SIBLING;
 
-	if (die_get_real_type(die_mem, &type_die) == NULL)
+	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;
+
+	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->reg = reg_from_dwarf_op(ops);
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index 892c8c5c23fc..cd481ec9c5a1 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -148,6 +148,8 @@ struct die_var_type {
 	u64 addr;
 	int reg;
 	int offset;
+	/* Whether the register holds a address to the type */
+	bool is_reg_var_addr;
 };
 
 /* Return type info of a member at offset */
-- 
2.51.0.261.g7ce5a0a67e-goog