dwarf_loader: Fix for BTF id drift caused by adding unspecified types
Recent changes to handle unspecified types (see [1]) cause BTF ID drift.
Specifically, the intent of commits [2], [3] and [4] is to render
references to unspecified types as void type. However, as a
consequence:
- in `die__process_unit()` call to `cu__add_tag()` allocates `small_id`
for unspecified type tags and adds these tags to `cu->types_table`;
- `btf_encoder__encode_tag()` skips generation of BTF entries for
`DW_TAG_unspecified_type` tags.
Such logic causes ID drift if unspecified type is not the last type
processed for compilation unit. `small_id` of each type following
unspecified type in the `cu->types_table` would have its BTF id off by
-1.
Thus, rendering references established on recode phase invalid.
This commit reverts `unspecified_type` id/tag tracking. Instead, the
following is done:
- `small_id` for unspecified type tags is set to 0, thus reference to
unspecified type tag would render BTF id of a `void` on recode phase;
- unspecified type tags are not added to `cu->types_table`.
This change also happens to fix issue reported in [5], the gist of that
issue is that the field `encoder->unspecified_type` is set but not reset
by function `btf_encoder__encode_cu()`. Thus, the following sequence of
events might occur when BTF encoding is requested:
- CU with unspecified type is processed:
- unspecified type id is 42
- encoder->unspecified_type is set to 42
- CU without unspecified type is processed next using the same `encoder`
object:
- some `struct foo` has id 42 in this CU
- the references to `struct foo` are set 0 by function
`btf_encoder__tag_type()`.
[1] https://lore.kernel.org/all/Y0R7uu3s%2FimnvPzM@kernel.org/
[2] bcc648a10cbc ("btf_encoder: Encode DW_TAG_unspecified_type returning routines as void")
[3] cffe5e1f75e1 ("core: Record if a CU has a DW_TAG_unspecified_type")
[4] 75e0fe28bb02 ("core: Add DW_TAG_unspecified_type to tag__is_tag_type() set")
[5] https://lore.kernel.org/bpf/Y%2FP1yxAuV6Wj3A0K@google.com/
Fixes: bcc648a10cbcd0b9 ("btf_encoder: Encode DW_TAG_unspecified_type returning routines as void")
Fixes: 52b25808e44a8e7f ("btf_encoder: Store type_id_off, unspecified type in encoder")
Reported-by: Matt Bobrowski <mattbobrowski@google.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Tested-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: KP Singh <kpsingh@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Yonghong Song <yhs@fb.com>
Cc: bpf@vger.kernel.org
Cc: dwarves@vger.kernel.org
Cc: kernel-team@fb.com
Link: https://lore.kernel.org/r/20230228202357.2766051-1-eddyz87@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
3 files changed
