Re: [PATCH v4 5/6] perf annotate-data: Fix libdw API contract violations

Namhyung Kim
2026-05-03T23:53:58Z

On Sun, May 03, 2026 at 10:10:31AM -0700, Ian Rogers wrote:
> Check return values of `dwarf_aggregate_size` and `dwarf_formudata`.
>
> Additionally:
> - Avoid `vfprintf` undefined behavior with `NULL` strings by using
> the `die_name()` helper for `dwarf_diename()` in `pr_*` calls.
> - Use `die_get_data_member_location()` (updated to use
> `dwarf_attr_integrate`) to correctly parse location expressions
> for inherited member locations in the fallback path when
> `dwarf_formudata()` fails.
>
> Fixes: 2bc3cf575a16 ("perf annotate-data: Improve debug message with location info")
> Fixes: 4a111cadac85 ("perf annotate-data: Add member field in the data type")
> Fixes: 8b1042c425f6 ("perf annotate-data: Set bitfield member offset and size properly")
> Fixes: fc044c53b99f ("perf annotate-data: Add dso->data_types tree")
> Assisted-by: Gemini-CLI:Google Gemini 3
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> v4:
> - Safe DWARF name printing in annotate-data.
> - Fix fallback location expression parsing for inherited data members.
> ---
> tools/perf/util/annotate-data.c | 27 +++++++++++++++++----------
> 1 file changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
> index 1eff0a27237d..2eacbba51f32 100644
> --- a/tools/perf/util/annotate-data.c
> +++ b/tools/perf/util/annotate-data.c
> @@ -74,7 +74,8 @@ void pr_debug_type_name(Dwarf_Die *die, enum type_state_kind kind)
> break;
> }
>
> - dwarf_aggregate_size(die, &size);
> + if (dwarf_aggregate_size(die, &size) != 0)
> + size = 0;
>
> strbuf_init(&sb, 32);
> die_get_typename_from_type(die, &sb);
> @@ -146,9 +147,9 @@ static void pr_debug_scope(Dwarf_Die *scope_die)
>
> tag = dwarf_tag(scope_die);
> if (tag == DW_TAG_subprogram)
> - pr_info("[function] %s\n", dwarf_diename(scope_die));
> + pr_info("[function] %s\n", die_name(scope_die));
> else if (tag == DW_TAG_inlined_subroutine)
> - pr_info("[inlined] %s\n", dwarf_diename(scope_die));
> + pr_info("[inlined] %s\n", die_name(scope_die));
> else if (tag == DW_TAG_lexical_block)
> pr_info("[block]\n");
> else
> @@ -250,9 +251,12 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
> if (dwarf_aggregate_size(&die_mem, &size) < 0)
> size = 0;
>
> - if (dwarf_attr_integrate(die, DW_AT_data_member_location, &attr))
> - dwarf_formudata(&attr, &loc);
> - else {
> + if (dwarf_attr_integrate(die, DW_AT_data_member_location, &attr)) {
> + if (dwarf_formudata(&attr, &loc) != 0) {
> + if (die_get_data_member_location(die, &loc) != 0)
> + loc = 0;
> + }
> + } else {
> /* bitfield member */
> if (dwarf_attr_integrate(die, DW_AT_data_bit_offset, &attr) &&
> dwarf_formudata(&attr, &loc) == 0)
> @@ -273,7 +277,9 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
> dwarf_diename(die), (long)bit_size) < 0)
> member->var_name = NULL;
> } else {
> - member->var_name = strdup(dwarf_diename(die));
> + const char *name = dwarf_diename(die);
> +
> + member->var_name = strdup(name);

This can be: member->var_name = name ? strdup(name) : NULL;

Thanks,
Namhyung

> }
>
> if (member->var_name == NULL) {
> @@ -370,7 +376,8 @@ static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
> if (dwarf_tag(type_die) == DW_TAG_typedef)
> die_get_real_type(type_die, type_die);
>
> - dwarf_aggregate_size(type_die, &size);
> + if (dwarf_aggregate_size(type_die, &size) != 0)
> + size = 0;
>
> /* Check existing nodes in dso->data_types tree */
> key.self.type_name = type_name;
> @@ -1569,7 +1576,7 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
> offset = loc->offset;
>
> pr_debug_dtp("CU for %s (die:%#lx)\n",
> - dwarf_diename(&cu_die), (long)dwarf_dieoffset(&cu_die));
> + die_name(&cu_die), (long)dwarf_dieoffset(&cu_die));
>
> if (reg == DWARF_REG_PC) {
> if (get_global_var_type(&cu_die, dloc, dloc->ip, dloc->var_addr,
> @@ -1636,7 +1643,7 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
> }
>
> pr_debug_dtp("found \"%s\" (die: %#lx) in scope=%d/%d (die: %#lx) ",
> - dwarf_diename(&var_die), (long)dwarf_dieoffset(&var_die),
> + die_name(&var_die), (long)dwarf_dieoffset(&var_die),
> i+1, nr_scopes, (long)dwarf_dieoffset(&scopes[i]));
>
> if (reg == DWARF_REG_PC) {
> --
> 2.54.0.545.g6539524ca2-goog
>