linux-kernel - Re: [PATCH v2 bpf-next] libbpf: Improve debug message when the base BTF cannot be found

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Message-ID: <Z0YsIULqeCxeVVtF@bolson-desk>
Date: Tue, 26 Nov 2024 14:14:25 -0600
From: "Olson, Matthew" <matthew.olson@...el.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
CC: Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
	<bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
	<daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu
	<song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend
	<john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev
	<sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next] libbpf: Improve debug message when the base
 BTF cannot be found

On Tue, Nov 26, 2024 at 01:39:36PM -0600, Olson, Matthew wrote:
> On Tue, Nov 26, 2024 at 11:21:21AM -0800, Andrii Nakryiko wrote:
> > On Thu, Nov 21, 2024 at 5:07 PM Olson, Matthew <matthew.olson@...el.com> wrote:
> > >
> > > From 22ed11ee2153fc921987eac7de24f564da9f9230 Mon Sep 17 00:00:00 2001
> > > From: Ben Olson <matthew.olson@...el.com>
> > > Date: Thu, 21 Nov 2024 11:26:35 -0600
> > > Subject: [PATCH v2 bpf-next] libbpf: Improve debug message when the base BTF
> > >  cannot be found
> > >
> > > When running `bpftool` on a kernel module installed in `/lib/modules...`,
> > > this error is encountered if the user does not specify `--base-btf` to
> > > point to a valid base BTF (e.g. usually in `/sys/kernel/btf/vmlinux`).
> > > However, looking at the debug output to determine the cause of the error
> > > simply says `Invalid BTF string section`, which does not point to the
> > > actual source of the error. This just improves that debug message to tell
> > > users what happened.
> > >
> > > Signed-off-by: Ben Olson <matthew.olson@...el.com>
> > > ---
> > >
> > > Changed in v2:
> > >   * Made error message better reflect the condition
> > >
> > >  tools/lib/bpf/btf.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> > > index 12468ae0d573..a4ae2df68b91 100644
> > > --- a/tools/lib/bpf/btf.c
> > > +++ b/tools/lib/bpf/btf.c
> > > @@ -283,7 +283,7 @@ static int btf_parse_str_sec(struct btf *btf)
> > >      return -EINVAL;
> > >    }
> > >    if (!btf->base_btf && start[0]) {
> > > -    pr_debug("Invalid BTF string section\n");
> > > +    pr_debug("Malformed BTF string section, did you forget to provide base BTF?\n");
> > 
> > I'm not sure why, but this v2 didn't make it into patchworks, so I
> > can't apply it. Can you please resend?
> 
> Sure thing. Thanks.

Ah, I think I figured out why it didn't make it into patchworks; I'll resend
yet again.

> 
> > 
> > Also please make sure you don't change indentation (tabs -> spaces),
> > because it looks like that's what happened here.
> 
> Ach, rookie mistake. I'll add clang-format to my git hooks.
> 
> > 
> > >      return -EINVAL;
> > >    }
> > >    return 0;
> > > --
> > > 2.47.0
>