Em Fri, Mar 31, 2023 at 12:27:00AM +0300, Eduard Zingerman escreveu:
> Recent change to fprintf (see below) causes incorrect `type_fprintf()`
> behavior for pointers annotated with btf_type_tag, for example:
>
> $ cat tag-test.c
> #define __t __attribute__((btf_type_tag("t1")))
>
> struct foo {
> int __t *a;
> } g;
>
> $ clang -g -c tag-test.c -o tag-test.o && \
> pahole -J tag-test.o && pahole --sort -F dwarf tag-test.o
> struct foo {
> int a; /* 0 8 */
> ...
> };
>
> Note that `*` is missing in the pahole output.
> The issue is caused by `goto next_type` that jumps over the
> `tag__name()` that is responsible for pointer printing.
>
> As agreed in [1] `type__fprintf()` is modified to skip type tags for
> now and would be modified to emit type tags later.
>
> The change in `__tag__name()` is necessary to avoid the following behavior:
>
> $ cat tag-test.c
> #define __t __attribute__((btf_type_tag("t1")))
>
> struct foo {
> int __t *a;
> int __t __t *b;
> } g;
>
> $ clang -g -c tag-test.c -o tag-test.o && \
> pahole -J tag-test.o && pahole --sort -F dwarf tag-test.o
> struct foo {
> int * a; /* 0 8 */
> int * b; /* 8 8 */
> ...
> };
>
> Note the extra space before `*` for field `b`.
>
> The issue was reported and tracked down to the root cause by
> Arnaldo Carvalho de Melo.
>
> Links:
> [1] https://lore.kernel.org/dwarves/20230314230417.1507266-1-eddyz87@xxxxxxxxx/T/#md82b04f66867434524beec746138951f26a3977e
>
> Fixes: e7fb771f2649 ("fprintf: Correct names for types with btf_type_tag attribute")
> Reported-by: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
> Link: https://lore.kernel.org/dwarves/20230314230417.1507266-1-eddyz87@xxxxxxxxx/T/#mc630bcd474ddd64c70d237edd4e0590dc048d63d
> Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> ---
> dwarves_fprintf.c | 37 +++++++++++++++++++++++++++++--------
> 1 file changed, 29 insertions(+), 8 deletions(-)
>
> diff --git a/dwarves_fprintf.c b/dwarves_fprintf.c
> index 1e6147a..818db2d 100644
> --- a/dwarves_fprintf.c
> +++ b/dwarves_fprintf.c
> @@ -572,7 +572,6 @@ static const char *__tag__name(const struct tag *tag, const struct cu *cu,
> case DW_TAG_restrict_type:
> case DW_TAG_atomic_type:
> case DW_TAG_unspecified_type:
> - case DW_TAG_LLVM_annotation:
> type = cu__type(cu, tag->type);
> if (type == NULL && tag->type != 0)
> tag__id_not_found_snprintf(bf, len, tag->type);
> @@ -618,6 +617,13 @@ static const char *__tag__name(const struct tag *tag, const struct cu *cu,
> case DW_TAG_variable:
> snprintf(bf, len, "%s", variable__name(tag__variable(tag)));
> break;
> + case DW_TAG_LLVM_annotation:
> + type = cu__type(cu, tag->type);
> + if (type == NULL && tag->type != 0)
> + tag__id_not_found_snprintf(bf, len, tag->type);
> + else if (!tag__has_type_loop(tag, type, bf, len, NULL))
> + __tag__name(type, cu, bf, len, conf);
> + break;
> default:
> snprintf(bf, len, "%s%s", tag__prefix(cu, tag->tag, pconf),
> type__name(tag__type(tag)) ?: "");
> @@ -677,6 +683,22 @@ static size_t type__fprintf_stats(struct type *type, const struct cu *cu,
> return printed;
> }
>
> +static type_id_t skip_llvm_annotations(const struct cu *cu, type_id_t id)
> +{
> + struct tag *type;
> +
> + for (;;) {
> + if (id == 0)
> + break;
> + type = cu__type(cu, id);
> + if (type == NULL || type->tag != DW_TAG_LLVM_annotation || type->type == id)
> + break;
> + id = type->type;
> + }
> +
> + return id;
> +}
This part I didn't understand, do you see any possibility of a
DW_TAG_LLVM_annotation pointing to another DW_TAG_LLVM_annotation?
- Arnaldo
> +
> static size_t union__fprintf(struct type *type, const struct cu *cu,
> const struct conf_fprintf *conf, FILE *fp);
>
> @@ -778,19 +800,17 @@ inner_struct:
>
> next_type:
> switch (type->tag) {
> - case DW_TAG_pointer_type:
> - if (type->type != 0) {
> + case DW_TAG_pointer_type: {
> + type_id_t ptype_id = skip_llvm_annotations(cu, type->type);
> +
> + if (ptype_id != 0) {
> int n;
> - struct tag *ptype = cu__type(cu, type->type);
> + struct tag *ptype = cu__type(cu, ptype_id);
> if (ptype == NULL)
> goto out_type_not_found;
> n = tag__has_type_loop(type, ptype, NULL, 0, fp);
> if (n)
> return printed + n;
> - if (ptype->tag == DW_TAG_LLVM_annotation) {
> - type = ptype;
> - goto next_type;
> - }
> if (ptype->tag == DW_TAG_subroutine_type) {
> printed += ftype__fprintf(tag__ftype(ptype),
> cu, name, 0, 1,
> @@ -811,6 +831,7 @@ next_type:
> }
> }
> /* Fall Thru */
> + }
> default:
> print_default:
> printed += fprintf(fp, "%-*s %s", tconf.type_spacing,
> --
> 2.40.0
>
--
- Arnaldo
