netdev - Re: [PATCH bpf-next 2/6] libbpf: Collect static vs global info about functions

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Message-ID: <20200108201019.q4xtcdawor36rxyo@ast-mbp>
Date:   Wed, 8 Jan 2020 12:10:20 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/6] libbpf: Collect static vs global info about
 functions

On Wed, Jan 08, 2020 at 05:57:55PM +0000, Song Liu wrote:
> 
> 
> > On Jan 8, 2020, at 2:25 AM, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> > 
> > Alexei Starovoitov <ast@...nel.org> writes:
> > 
> >> Collect static vs global information about BPF functions from ELF file and
> >> improve BTF with this additional info if llvm is too old and doesn't emit it on
> >> its own.
> > 
> > Has the support for this actually landed in LLVM yet? I tried grep'ing
> > in the commit log and couldn't find anything...
> > 
> > [...]
> >> @@ -313,6 +321,7 @@ struct bpf_object {
> >> 	bool loaded;
> >> 	bool has_pseudo_calls;
> >> 	bool relaxed_core_relocs;
> >> +	bool llvm_emits_func_linkage;
> > 
> > Nit: s/llvm/compiler/? Presumably GCC will also support this at some
> > point?
> 
> Echoing this nit (and other references to llvm). Otherwise,

sure. will rename to compiler, but I think you folks are overly optimistic
about gcc. Even basic stuff doesn't work yet. I doubt we will see BTF
emitted by gcc this year.