Re: pahole v1.24: FAILED: load BTF from vmlinux: Invalid argument

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Aug 26, 2022 at 05:59:44AM +0300, Vitaly Chikunov wrote:
> On Fri, Aug 26, 2022 at 05:52:20AM +0300, Vitaly Chikunov wrote:
> > Arnaldo,
> > 
> > On Thu, Aug 25, 2022 at 08:16:20PM +0300, Vitaly Chikunov wrote:
> > > On Thu, Aug 25, 2022 at 01:47:59PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > On Thu, Aug 25, 2022, 1:35 PM Vitaly Chikunov <vt@altlinux.org> wrote:
> > > > >
> > > > > I also noticed that after upgrading pahole to v1.24 kernel build (tested on
> > > > > v5.18.19, v5.15.63, sorry for not testing on mainline) fails with:
> > > > >
> > > > >     BTFIDS  vmlinux
> > > > >   + ./tools/bpf/resolve_btfids/resolve_btfids vmlinux
> > > > >   FAILED: load BTF from vmlinux: Invalid argument
> > > > >
> > > > > Perhaps, .tmp_vmlinux.btf is generated incorrectly? Downgrading dwarves to
> > > > > v1.23 resolves the issue.
> > > > >
> > > > 
> > > > Can you try this, from Martin Reboredo (Archlinux):
> > > > 
> > > > Can you try a build of the kernel or the by passing the
> > > > --skip_encoding_btf_enum64 to scripts/pahole-flags.sh?
> > > > 
> > > > Here's a patch for either in tree scripts/pahole-flags.sh or
> > > > /usr/lib/modules/5.19.3-arch1-1/build/scripts/pahole-flags.sh
> > > 
> > > This patch helped and kernel builds successfully after applying it.
> > > (Didn't notice this suggestion in release discussion thread.)
> > 
> > Even thought it now compiles with this patch, it does not boot
> > afterwards (in virtme-like env), witch such console messages:
> 
> I'm talking here about 5.15.62. Yes, proposed patch does not apply there
> (since there is no `scripts/pahole-flags.sh`), but I updated
> `scripts/link-vmlinux.sh` with the similar `if` to append
> `--skip_encoding_btf_enum64` which lets then compilation pass.
> 
> Thanks,
> 
> > 
> >   [    0.767649] Run /init as init process
> >   [    0.770858] BPF:[593] ENUM perf_event_task_context
> >   [    0.771262] BPF:size=4 vlen=4
> >   [    0.771511] BPF:
> >   [    0.771680] BPF:Invalid btf_info kind_flag
> >   [    0.772016] BPF:

I can see the same on 5.15, it looks like the libbpf change that
pahole is compiled with is setting the type's kflag for values < 0:
(which is the case for perf_event_task_context enum first value)

  dffbbdc2d988 libbpf: Add enum64 parsing and new enum64 public API

but IIUC kflag should stay zero for normal enum otherwise the btf meta
verifier screams

if I compile pahole with the libbpf change below I can boot 5.15 kernel
normally

Yonghong, any idea?

thanks,
jirka


---
diff --git a/src/btf.c b/src/btf.c
index 2d14f1a52d7a..53d7516e4b89 100644
--- a/src/btf.c
+++ b/src/btf.c
@@ -2151,10 +2151,6 @@ int btf__add_enum_value(struct btf *btf, const char *name, __s64 value)
 	t = btf_last_type(btf);
 	btf_type_inc_vlen(t);
 
-	/* if negative value, set signedness to signed */
-	if (value < 0)
-		t->info = btf_type_info(btf_kind(t), btf_vlen(t), true);
-
 	btf->hdr->type_len += sz;
 	btf->hdr->str_off += sz;
 	return 0;