On Sat, Jan 2, 2021 at 3:07 PM Jiri Olsa <jo...@redhat.com> wrote: > > On Sat, Jan 02, 2021 at 02:25:34PM -0800, Andrii Nakryiko wrote: > > SNIP > > > > > > > so your .config has > > > CONFIG_CRYPTO_DEV_BCM_SPU=y > > > > > > and that defines 'struct device_private' which > > > clashes with the same struct defined in drivers/base/base.h > > > > > > so several networking structs will be doubled, like net_device: > > > > > > $ bpftool btf dump file ../vmlinux.config | grep net_device\' | > > > grep STRUCT > > > [2731] STRUCT 'net_device' size=2240 vlen=133 > > > [113981] STRUCT 'net_device' size=2240 vlen=133 > > > > > > each is using different 'struct device_private' when it's unwinded > > > > > > and that will confuse BTFIDS logic, becase we have multiple structs > > > with the same name, and we can't be sure which one to pick > > > > > > perhaps we should check on this in pahole and warn earlier with > > > better error message.. I'll check, but I'm not sure if pahole can > > > survive another hastab ;-) > > > > > > Andrii, any ideas on this? ;-) > > > > It's both unavoidable and correct from the C type system's > > perspective, so there is nothing for pahole to warn about. We used to > > have (for a long time) a similar clash with two completely different > > ring_buffer structs. Eventually they just got renamed to avoid > > duplication of related structs (task_struct and tons of other). But > > both BTF dedup and CO-RE relocation algorithms are designed to handle > > this correctly, ... > > AFAIU it's all correctly dedulicated, but still all structs that > contain (at some point) 'struct device_private' will appear twice > in BTF data.. each with different 'struct device_private'
it's correct from the type system perspective, right. Those two duplicates of struct device_private are parts of two different hierarchies of types. However inconvenient it is, C allows it, unfortunately :( > > > ... so perhaps BTFIDS should be able to handle this as > > well? > > hm, BTFIDS sees BTF data with two same struct names and has no > way to tell which one to use > > unless we have some annotation data for BTF types I don't > see a way to handle this correctly.. but I think we can > detect this directly in BTFIDS and print more accurate error > message > > as long as we dont see this on daily basis, I think that better > error message + following struct rename is good solution Perhaps warning and handling this gracefully is a bit better way to handle this. Renaming is definitely good, but shouldn't block the kernel build process. I don't remember the exact details for why duplicate struct would cause troubles for resolve_btfids, but maybe just picking the struct with minimal ID (out of 2+ duplicates) would be ok in practice most of the time. In any case, that's what most users (including libbpf) will do, when searching for the type by name. > > > > > > > > > easy fix is the patch below that renames the bcm's structs, > > > it makes the kernel to compile.. but of course the new name > > > is probably wrong and we should push this through that code > > > authors > > > > In this case, I think renaming generic device_private name is a good > > thing regardless. > > ok, I'll send the change > great, thanks > jirka >
