[PATCH v2 07/11] perf annotate-data: Handle global variable access with const register

[Zecheng Li]

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. This is only done for kernel DSOs since the pattern relies on
kernel-specific global variable resolution. We could also treat
registers with integer types to the global variable path, but this
requires more changes.

Signed-off-by: Zecheng Li <zli94@xxxxxxxx>
---
 tools/perf/util/annotate-data.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 301f73ea8275..50c82c91f828 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -1229,6 +1229,11 @@ 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 &&
+	    dso__kernel(map__dso(dloc->ms->map))) {
+		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;
-- 
2.53.0