From: Namhyung Kim <namhyung@kernel.org>
To: Zecheng Li <zli94@ncsu.edu>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Ian Rogers <irogers@google.com>,
Adrian Hunter <adrian.hunter@intel.com>,
James Clark <james.clark@linaro.org>,
xliuprof@google.com, linux-perf-users@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 02/11] perf dwarf-aux: Add die_get_pointer_type to get pointer types
Date: Tue, 10 Feb 2026 18:17:32 -0800 [thread overview]
Message-ID: <aYvmvNUcoXpNOBW0@google.com> (raw)
In-Reply-To: <20260127020617.2804780-3-zli94@ncsu.edu>
On Mon, Jan 26, 2026 at 09:04:55PM -0500, Zecheng Li wrote:
> When a variable type is wrapped in typedef/qualifiers, callers may need
> to first resolve it to the underlying DW_TAG_pointer_type or
> DW_TAG_array_type. A simple tag check is not enough and directly calling
> __die_get_real_type() can stop at the pointer type (e.g. typedef ->
> pointer) instead of the pointee type.
>
> Add die_get_pointer_type() helper that follows typedef/qualifier chains
> and returns the underlying pointer DIE. Use it in annotate-data.c so
> pointer checks and dereference work correctly for typedef'd pointers.
>
> Signed-off-by: Zecheng Li <zli94@ncsu.edu>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Thanks,
Namhyung
> ---
> tools/perf/util/annotate-data.c | 39 +++++++++++++++++++--------------
> tools/perf/util/dwarf-aux.c | 27 +++++++++++++++++++++++
> tools/perf/util/dwarf-aux.h | 2 ++
> 3 files changed, 51 insertions(+), 17 deletions(-)
>
> diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
> index 99ffc6d70565..8ff1972981b7 100644
> --- a/tools/perf/util/annotate-data.c
> +++ b/tools/perf/util/annotate-data.c
> @@ -455,13 +455,6 @@ static const char *match_result_str(enum type_match_result tmr)
> }
> }
>
> -static bool is_pointer_type(Dwarf_Die *type_die)
> -{
> - int tag = dwarf_tag(type_die);
> -
> - return tag == DW_TAG_pointer_type || tag == DW_TAG_array_type;
> -}
> -
> static bool is_compound_type(Dwarf_Die *type_die)
> {
> int tag = dwarf_tag(type_die);
> @@ -474,19 +467,24 @@ static bool is_better_type(Dwarf_Die *type_a, Dwarf_Die *type_b)
> {
> Dwarf_Word size_a, size_b;
> Dwarf_Die die_a, die_b;
> + Dwarf_Die ptr_a, ptr_b;
> + Dwarf_Die *ptr_type_a, *ptr_type_b;
> +
> + ptr_type_a = die_get_pointer_type(type_a, &ptr_a);
> + ptr_type_b = die_get_pointer_type(type_b, &ptr_b);
>
> /* pointer type is preferred */
> - if (is_pointer_type(type_a) != is_pointer_type(type_b))
> - return is_pointer_type(type_b);
> + if ((ptr_type_a != NULL) != (ptr_type_b != NULL))
> + return ptr_type_b != NULL;
>
> - if (is_pointer_type(type_b)) {
> + if (ptr_type_b) {
> /*
> * We want to compare the target type, but 'void *' can fail to
> * get the target type.
> */
> - if (die_get_real_type(type_a, &die_a) == NULL)
> + if (die_get_real_type(ptr_type_a, &die_a) == NULL)
> return true;
> - if (die_get_real_type(type_b, &die_b) == NULL)
> + if (die_get_real_type(ptr_type_b, &die_b) == NULL)
> return false;
>
> type_a = &die_a;
> @@ -539,7 +537,7 @@ static enum type_match_result check_variable(struct data_loc_info *dloc,
> * and local variables are accessed directly without a pointer.
> */
> if (needs_pointer) {
> - if (!is_pointer_type(type_die) ||
> + if (die_get_pointer_type(type_die, type_die) == NULL ||
> __die_get_real_type(type_die, type_die) == NULL)
> return PERF_TMR_NO_POINTER;
> }
> @@ -880,12 +878,16 @@ static void update_var_state(struct type_state *state, struct data_loc_info *dlo
> continue;
>
> if (var->reg == DWARF_REG_FB || var->reg == fbreg || var->reg == state->stack_reg) {
> + Dwarf_Die ptr_die;
> + Dwarf_Die *ptr_type;
> int offset = var->offset;
> struct type_state_stack *stack;
>
> + ptr_type = die_get_pointer_type(&mem_die, &ptr_die);
> +
> /* 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)
> + if (!var->is_reg_var_addr && ptr_type &&
> + __die_get_real_type(ptr_type, &mem_die) == NULL)
> continue;
>
> if (var->reg != DWARF_REG_FB)
> @@ -1110,7 +1112,9 @@ static enum type_match_result check_matching_type(struct type_state *state,
> goto check_non_register;
>
> if (state->regs[reg].kind == TSR_KIND_TYPE) {
> + Dwarf_Die ptr_die;
> Dwarf_Die sized_type;
> + Dwarf_Die *ptr_type;
> struct strbuf sb;
>
> strbuf_init(&sb, 32);
> @@ -1122,7 +1126,8 @@ static enum type_match_result check_matching_type(struct type_state *state,
> * Normal registers should hold a pointer (or array) to
> * dereference a memory location.
> */
> - if (!is_pointer_type(&state->regs[reg].type)) {
> + ptr_type = die_get_pointer_type(&state->regs[reg].type, &ptr_die);
> + if (!ptr_type) {
> if (dloc->op->offset < 0 && reg != state->stack_reg)
> goto check_kernel;
>
> @@ -1130,7 +1135,7 @@ static enum type_match_result check_matching_type(struct type_state *state,
> }
>
> /* Remove the pointer and get the target type */
> - if (__die_get_real_type(&state->regs[reg].type, type_die) == NULL)
> + if (__die_get_real_type(ptr_type, type_die) == NULL)
> return PERF_TMR_NO_POINTER;
>
> dloc->type_offset = dloc->op->offset + state->regs[reg].offset;
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index b57cdc8860f0..96cfcbd40c45 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -303,6 +303,33 @@ Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem)
> return vr_die;
> }
>
> +/**
> + * die_get_pointer_type - Get a pointer/array type die
> + * @type_die: a DIE of a type
> + * @die_mem: where to store a type DIE
> + *
> + * Get a pointer/array type DIE from @type_die. If the type is a typedef or
> + * qualifier (const, volatile, etc.), follow the chain to find the underlying
> + * pointer type.
> + */
> +Dwarf_Die *die_get_pointer_type(Dwarf_Die *type_die, Dwarf_Die *die_mem)
> +{
> + int tag;
> +
> + do {
> + tag = dwarf_tag(type_die);
> + if (tag == DW_TAG_pointer_type || tag == DW_TAG_array_type)
> + return type_die;
> + if (tag != DW_TAG_typedef && tag != DW_TAG_const_type &&
> + tag != DW_TAG_restrict_type && tag != DW_TAG_volatile_type &&
> + tag != DW_TAG_shared_type)
> + return NULL;
> + type_die = die_get_type(type_die, die_mem);
> + } while (type_die);
> +
> + return NULL;
> +}
> +
> /* Get attribute and translate it as a udata */
> static int die_get_attr_udata(Dwarf_Die *tp_die, unsigned int attr_name,
> Dwarf_Word *result)
> diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
> index b3ee5df0b6be..8045281f219c 100644
> --- a/tools/perf/util/dwarf-aux.h
> +++ b/tools/perf/util/dwarf-aux.h
> @@ -60,6 +60,8 @@ Dwarf_Die *die_get_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem);
> Dwarf_Die *__die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem);
> /* Get a type die, but skip qualifiers and typedef */
> Dwarf_Die *die_get_real_type(Dwarf_Die *vr_die, Dwarf_Die *die_mem);
> +/* Get a pointer/array type, following typedefs/qualifiers */
> +Dwarf_Die *die_get_pointer_type(Dwarf_Die *type_die, Dwarf_Die *die_mem);
>
> /* Check whether the DIE is signed or not */
> bool die_is_signed_type(Dwarf_Die *tp_die);
> --
> 2.52.0
>
next prev parent reply other threads:[~2026-02-11 2:17 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-27 2:04 [PATCH v1 00/11] perf tools: Improvements to data type profiler Zecheng Li
2026-01-27 2:04 ` [PATCH v1 01/11] perf dwarf-aux: Skip check_variable for die_find_variable_by_reg Zecheng Li
2026-02-11 2:08 ` Namhyung Kim
2026-01-27 2:04 ` [PATCH v1 02/11] perf dwarf-aux: Add die_get_pointer_type to get pointer types Zecheng Li
2026-02-11 2:17 ` Namhyung Kim [this message]
2026-01-27 2:04 ` [PATCH v1 03/11] perf dwarf-aux: Preserve typedefs in match_var_offset Zecheng Li
2026-02-11 2:23 ` Namhyung Kim
2026-01-27 2:04 ` [PATCH v1 04/11] perf annotate-data: Improve type comparison from different scopes Zecheng Li
2026-02-11 2:25 ` Namhyung Kim
2026-01-27 2:04 ` [PATCH v1 05/11] perf dwarf-aux: Handle array types in die_get_member_type Zecheng Li
2026-01-27 2:04 ` [PATCH v1 06/11] perf annotate-data: Collect global variables without name Zecheng Li
2026-02-11 2:29 ` Namhyung Kim
2026-01-27 2:05 ` [PATCH v1 07/11] perf annotate-data: Handle global variable access with const register Zecheng Li
2026-02-11 2:37 ` Namhyung Kim
2026-01-27 2:05 ` [PATCH v1 08/11] perf annotate-data: Add invalidate_reg_state() helper for x86 Zecheng Li
2026-02-11 2:38 ` Namhyung Kim
2026-01-27 2:05 ` [PATCH v1 09/11] perf annotate-data: Invalidate caller-saved regs for all calls Zecheng Li
2026-01-27 2:05 ` [PATCH v1 10/11] perf annotate-data: Use DWARF location ranges to preserve reg state Zecheng Li
2026-01-27 2:05 ` [PATCH v1 11/11] perf dwarf-aux: Collect all variable locations for insn tracking Zecheng Li
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