linux-kernel - Re: [PATCH bpf-next v2 04/13] resolve_btfids: Introduce finalize

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Message-ID: <b92382bdb9b9b274c0eda1d2bf8aba69c9768ecd.camel@gmail.com>
Date: Tue, 20 Jan 2026 10:19:10 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>, Alexei Starovoitov
 <ast@...nel.org>,  Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Mykyta Yatsenko <yatsenko@...a.com>, Tejun Heo <tj@...nel.org>, Alan
 Maguire <alan.maguire@...cle.com>, Benjamin Tissoires <bentiss@...nel.org>,
 Jiri Kosina	 <jikos@...nel.org>, Amery Hung <ameryhung@...il.com>,
 bpf@...r.kernel.org, 	linux-kernel@...r.kernel.org,
 linux-input@...r.kernel.org, 	sched-ext@...ts.linux.dev
Subject: Re: [PATCH bpf-next v2 04/13] resolve_btfids: Introduce
 finalize_btf() step

On Tue, 2026-01-20 at 10:11 -0800, Ihor Solodrai wrote:

[...]

> > > @@ -1099,12 +1116,22 @@ int main(int argc, const char **argv)
> > >  	if (obj.efile.idlist_shndx == -1 ||
> > >  	    obj.efile.symbols_shndx == -1) {
> > >  		pr_debug("Cannot find .BTF_ids or symbols sections, skip symbols resolution\n");
> > > -		goto dump_btf;
> > > +		resolve_btfids = false;
> > >  	}
> > >  
> > > -	if (symbols_collect(&obj))
> > > +	if (resolve_btfids)
> > > +		if (symbols_collect(&obj))
> > > +			goto out;
> > 
> > Nit: check obj.efile.idlist_shndx and obj.efile.symbols_shndx inside symbols_collect()?
> >      To avoid resolve_btfids flag and the `goto dump_btf;` below.
> 
> Hi Eduard, thank you for review.
> 
> The issue is that in case of .BTF_ids section absent we have to skip
> some of the steps, specifically:
>   - symbols_collect()
>   - sequence between symbols_resolve() and dump_raw_btf_ids()

> It's not an exit condition, we still have to do load/dump of the BTF.
> 
> I tried in symbols_collect():
> 
> 	if (obj.efile.idlist_shndx == -1 || obj.efile.symbols_shndx == -1)
> 		return 0;
> 
> But then, we either have to do the same check in symbols_resolve() and
> co, or maybe store a flag in the struct object.  So I decided it's
> better to have an explicit flag in the main control flow, instead of
> hiding it.

For symbols_resolve() is any special logic necessary?
I think that `id = btf_id__find(root, str);` will just return NULL for
every type, thus the whole function would be a noop passing through
BTF types once.

symbols_patch() will be a noop, as it will attempt traversing empty roots.
dump_raw_btf_ids() already returns if there are no .BTF_ids.

[...]