On Mon, Feb 27, 2023 at 9:48 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote: > > On Mon, 2023-02-27 at 11:31 -0800, Andrii Nakryiko wrote: > [...] > > > > I'd start with understanding what BTF and DWARF differences are > > > > causing the issue before trying to come up with the fix. For that we > > > > don't even need config or repro steps, it should be enough to share > > > > vmlinux with BTF and DWARF, and start from there. > > > > > > > > > > Yes, I suspect that there is some kind of unanticipated > > > anomaly for some DWARF encoding for some kind of objects, > > > just need to find the root for the diverging type hierarchies. > > > > > > > But I'm sure Eduard is on top of this already (especially that he can > > > > repro the issue now). > > > > > > I'm working on it, nothing to report yet, but I'm working on it. > > > > > > > Thanks, please keep us posted! > > It is interesting how everything is interconnected. The patch for > pahole below happens to help. I prepared it last week while working on > new DWARF encoding scheme for btf_type_tag. > > I still need to track down which "unspecified_type" entries caused the > issue in this particular case. Will post an update tomorrow. > > Meanwhile, Matt, KP, could you please verify the patch on your side? > It is for the "next" branch of pahole. > > --- > > From 09fac63ca08e25aea499f827283b07cc87a7daab Mon Sep 17 00:00:00 2001 > From: Eduard Zingerman <eddyz87@xxxxxxxxx> > Date: Tue, 21 Feb 2023 19:23:00 +0200 > Subject: [PATCH] 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 renders references established on recode phase invalid. > > This commit reverts `unspecified_type` id/tag tracking, instead: > - `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`. > > [1] https://lore.kernel.org/all/Y0R7uu3s%2FimnvPzM@xxxxxxxxxx/ > [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") > > Fixes: bcc648a10cbc ("btf_encoder: Encode DW_TAG_unspecified_type returning routines as void") > Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx> Tested-by: KP Singh <kpsingh@xxxxxxxxxx> Reported-by: Matt Bobrowski <mattbobrowski@xxxxxxxxxx> Thank you so much Eduard, this worked: * No duplicate BTF ID warnings * No 15 minute BTF ID generation * Matt's reproducer loads successfully. I had a sneaky suspicion that it was these unspecified types, which is why my hacky patch which got unspecified types out of the way got things to *mostly* work.
