netdev - Re: [PATCH bpf] libbpf: handle GCC noreturn-turned-volatile quirk

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Message-ID: <e7b34bdc-31d0-8137-9189-f0f03339d33d@iogearbox.net>
Date:   Wed, 10 Jun 2020 13:38:24 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Andrii Nakryiko <andriin@...com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, ast@...com, jean-philippe@...aro.org
Cc:     andrii.nakryiko@...il.com, kernel-team@...com
Subject: Re: [PATCH bpf] libbpf: handle GCC noreturn-turned-volatile quirk

On 6/10/20 7:23 AM, Andrii Nakryiko wrote:
> Handle a GCC quirk of emitting extra volatile modifier in DWARF (and
> subsequently preserved in BTF by pahole) for function pointers marked as
> __attribute__((noreturn)). This was the way to mark such functions before GCC
> 2.5 added noreturn attribute. Drop such func_proto modifiers, similarly to how
> it's done for array (also to handle GCC quirk/bug).
> 
> Such volatile attribute is emitted by GCC only, so existing selftests can't
> express such test. Simple repro is like this (compiled with GCC + BTF
> generated by pahole):
> 
>    struct my_struct {
>        void __attribute__((noreturn)) (*fn)(int);
>    };
>    struct my_struct a;
> 
> Without this fix, output will be:
> 
> struct my_struct {
>      voidvolatile  (*fn)(int);
> };
> 
> With the fix:
> 
> struct my_struct {
>      void (*fn)(int);
> };
> 
> Reported-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Fixes: 351131b51c7a ("libbpf: add btf_dump API for BTF-to-C conversion")
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Applied, thanks!