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

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Message-ID: <aLJSWXAUVBqSFYPL@google.com>
Date: Fri, 29 Aug 2025 18:22:33 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Zecheng Li <zecheng@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...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>,
	Xu Liu <xliuprof@...gle.com>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/10] perf dwarf-aux: Better variable collection for
 insn tracking

On Mon, Aug 25, 2025 at 07:54:05PM +0000, Zecheng Li wrote:
> 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>

Reviewed-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung

> ---
>  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
>