Re: Kernel build fail with 'btf_encoder__encode: btf__dedup failed!'

["Daniel Xu" <dxu@dxuuu.xyz>]

On Sun, Jan 22, 2023, at 10:48 AM, Daniel Xu wrote:
> Hi,
>
> I'm getting the following error during build:
>
>         $ ./tools/testing/selftests/bpf/vmtest.sh -j30
>         [...]
>           BTF     .btf.vmlinux.bin.o
>         btf_encoder__encode: btf__dedup failed!
>         Failed to encode BTF
>           LD      .tmp_vmlinux.kallsyms1
>           NM      .tmp_vmlinux.kallsyms1.syms
>           KSYMS   .tmp_vmlinux.kallsyms1.S
>           AS      .tmp_vmlinux.kallsyms1.S
>           LD      .tmp_vmlinux.kallsyms2
>           NM      .tmp_vmlinux.kallsyms2.syms
>           KSYMS   .tmp_vmlinux.kallsyms2.S
>           AS      .tmp_vmlinux.kallsyms2.S
>           LD      .tmp_vmlinux.kallsyms3
>           NM      .tmp_vmlinux.kallsyms3.syms
>           KSYMS   .tmp_vmlinux.kallsyms3.S
>           AS      .tmp_vmlinux.kallsyms3.S
>           LD      vmlinux
>           BTFIDS  vmlinux
>         FAILED: load BTF from vmlinux: No such file or directory
>         make[1]: *** [scripts/Makefile.vmlinux:35: vmlinux] Error 255
>         make[1]: *** Deleting file 'vmlinux'
>         make: *** [Makefile:1264: vmlinux] Error 2
>
> This happens on both bpf-next/master (84150795a49) and 6.2-rc5
> (2241ab53cb).
>
> I've also tried arch linux pahole 1:1.24+r29+g02d67c5-1 as well as
> upstream pahole on master (02d67c5176) and upstream pahole on
> next (2ca56f4c6f659).
>
> Of the above 6 combinations, I think I've tried all of them (maybe
> missing 1 or 2).
>
> Looks like GCC got updated recently on my machine, so perhaps
> it's related?
>
>         CONFIG_CC_VERSION_TEXT="gcc (GCC) 12.2.1 20230111"
>
> I'll try some debugging, but just wanted to report it first.
>
> Thanks,
> Daniel

Applying the following diff:

diff --git a/src/btf.c b/src/btf.c
index ae1520f..8a2fa36 100644
--- a/src/btf.c
+++ b/src/btf.c
@@ -4576,8 +4576,11 @@ static int btf_dedup_ref_type(struct btf_dedup *d, __u32 type_id)
        int ref_type_id;
        long h;

-       if (d->map[type_id] == BTF_IN_PROGRESS_ID)
+       if (d->map[type_id] == BTF_IN_PROGRESS_ID) {
+               struct btf_type *t = btf_type_by_id(d->btf, type_id);
+               pr_warn("eloop type_id=%d, kind=%d, type=%d\n", type_id, btf_kind(t), t->type);
                return -ELOOP;
+       }
        if (d->map[type_id] <= BTF_MAX_NR_TYPES)
                return resolve_type_id(d, type_id);

Yields:

          BTF     .btf.vmlinux.bin.o
        libbpf: eloop type_id=2, kind=10, type=2
        btf_encoder__encode: btf__dedup failed!
        Failed to encode BTF

So it's a CONST pointing to itself?

I'm somewhat out of ideas here.