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

[Namhyung Kim <namhyung@kernel.org>]

On Mon, Jan 26, 2026 at 09:05:00PM -0500, Zecheng Li wrote:
> 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.

I'm thinking of how we can support user binaries with this code pattern.
For now, I think it's ok for the kernel, but at least we need to check
if dso__kernel(map__dso(dloc->ms->map)) is not zero (DSO_SPACE__USER).

Thanks,
Namhyung

> 
> Signed-off-by: Zecheng Li <zli94@ncsu.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
>