linux-kernel - [PATCH v1 07/11] perf annotate-data: Handle global variable access with const register

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Message-ID: <20260127020617.2804780-8-zli94@ncsu.edu>
Date: Mon, 26 Jan 2026 21:05:00 -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 07/11] perf annotate-data: Handle global variable access with const register

When a register holds a constant value (TSR_KIND_CONST) and is used with
a negative offset, treat it as a potential global variable access
instead of falling through to CFA (frame) handling.

This fixes cases like array indexing with computed offsets:

    movzbl -0x7d72725a(%rax), %eax   # array[%rax]

Where %rax contains a computed index and the negative offset points to a
global array. Previously this fell through to the CFA path which doesn't
handle global variables, resulting in "no type information".

The fix redirects such accesses to check_kernel which calls
get_global_var_type() to resolve the type from the global variable
cache. We could also treat registers with integer types to the global
variable path, but this requires more changes.

Signed-off-by: Zecheng Li <zli94@...u.edu>
---
 tools/perf/util/annotate-data.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 970238bc81b7..177aa6634504 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -1230,6 +1230,10 @@ static enum type_match_result check_matching_type(struct type_state *state,
 		return PERF_TMR_BAIL_OUT;
 	}

+	if (state->regs[reg].kind == TSR_KIND_CONST) {
+		if (dloc->op->offset < 0 && reg != state->stack_reg && reg != dloc->fbreg)
+			goto check_kernel;
+	}
 check_non_register:
 	if (reg == dloc->fbreg || reg == state->stack_reg) {
 		struct type_state_stack *stack;
-- 
2.52.0