Re: [PATCH v2 13/16] perf annotate-arm64: Support 'add' instruction tracking

[Namhyung Kim]

On Fri, Apr 03, 2026 at 09:47:57AM +0000, Tengda Wu wrote:
> Extend update_insn_state() for arm64 to track pointer arithmetic and
> member address calculations.
> 
> The arm64 'add' instruction frequently calculates structure member
> addresses, such as 'add x0, x1, #offset'. Tracking this is essential
> to maintain the connection between a base pointer and its derived
> member addresses.

What about other arithmetic instructions?  Can 'sub' be used in a
similar manner?  Maybe we want to invalidate the target register state
for all(?) other instructions.

Thanks,
Namhyung

> 
> The implementation checks if the base register contains a pointer
> or a structure type. When an immediate offset is added, use
> die_get_member_type() to verify that the resulting offset points to
> a valid member within the data type. If valid, update the target
> register's type state with the new offset while preserving the base
> type information.
> 
> A real-world example is shown below:
> 
>   ffff80008001c9a8 <flush_ptrace_hw_breakpoint>:
>   ffff80008001c9c4:  add  x19, x0, #0xeb8 // x0 (task_struct*) + 0xeb8 -> x19
>   ffff80008001c9d0:  ldr  x0, [x19]       // PMU sample
> 
> Before this commit, the type flow broke at the 'add' instruction,
> leaving the subsequent load with no type information:
> 
>   chk [28] reg19 offset=0 ok=0 kind=0 cfa : no type information
>   final result: no type information
> 
> After this commit, the tracker correctly follows the member address
> calculation:
> 
>   var [0] reg0 offset 0 type='struct task_struct*'
>   add [1c] address of 0xeb8(reg0) -> reg19 type='struct task_struct*'
>   chk [28] reg19 offset=0 ok=1 kind=1 (struct task_struct*) : Good!
>   found by insn track: 0(reg19) type-offset=0xeb8
>   final result: type='struct task_struct'
> 
> Signed-off-by: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
> ---
>  .../perf/util/annotate-arch/annotate-arm64.c  | 45 +++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/tools/perf/util/annotate-arch/annotate-arm64.c b/tools/perf/util/annotate-arch/annotate-arm64.c
> index 013b673f4861..d2557b9d6909 100644
> --- a/tools/perf/util/annotate-arch/annotate-arm64.c
> +++ b/tools/perf/util/annotate-arch/annotate-arm64.c
> @@ -7,6 +7,7 @@
>  #include <linux/zalloc.h>
>  #include <linux/string.h>
>  #include <regex.h>
> +#include <inttypes.h>
>  #include "../annotate.h"
>  #include "../disasm.h"
>  #include "../annotate-data.h"
> @@ -308,6 +309,50 @@ static void update_insn_state_arm64(struct type_state *state,
>  	sreg = src->reg1;
>  	dreg = dst->reg1;
>  
> +	if (!strcmp(dl->ins.name, "add")) {
> +		struct type_state_reg dst_tsr;
> +
> +		if (!has_reg_type(state, sreg) ||
> +		    !has_reg_type(state, dreg) ||
> +		    !state->regs[dreg].ok)
> +			return;
> +
> +		tsr = &state->regs[sreg];
> +		tsr->copied_from = -1;
> +		dst_tsr = state->regs[dreg];
> +
> +		/* Handle calculation of a register holding a typed pointer */
> +		if (dst_tsr.kind == TSR_KIND_POINTER ||
> +		    (dst_tsr.kind == TSR_KIND_TYPE &&
> +		    dwarf_tag(&dst_tsr.type) == DW_TAG_pointer_type)) {
> +			s32 offset;
> +
> +			if (dst_tsr.kind == TSR_KIND_TYPE &&
> +			    __die_get_real_type(&dst_tsr.type, &type_die) == NULL)
> +				return;
> +
> +			if (dst_tsr.kind == TSR_KIND_POINTER)
> +				type_die = dst_tsr.type;
> +
> +			/* Check if the target type has a member at the new offset */
> +			offset = dst->offset + dst_tsr.offset;
> +			if (die_get_member_type(&type_die, offset, &type_die) == NULL)
> +				return;
> +
> +			tsr->type = dst_tsr.type;
> +			tsr->kind = dst_tsr.kind;
> +			tsr->offset = offset;
> +			tsr->ok = true;
> +
> +			pr_debug_dtp("add [%x] address of %s%#x(reg%d) -> reg%d",
> +				     insn_offset, dst->offset < 0 ? "-" : "",
> +				     abs(dst->offset), dreg, sreg);
> +
> +			pr_debug_type_name(&tsr->type, tsr->kind);
> +		}
> +		return;
> +	}
> +
>  	/* Register to register transfers */
>  	if (!strcmp(dl->ins.name, "mov")) {
>  		if (!has_reg_type(state, sreg))
> -- 
> 2.34.1
>