netdev - Re: [PATCH bpf-next v4 03/10] bpf: btf: Check members of struct/union

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Message-ID: <20180418113025.4ad5b9bd@cakuba.netronome.com>
Date:   Wed, 18 Apr 2018 11:30:25 -0700
From:   Jakub Kicinski <kubakici@...pl>
To:     Martin KaFai Lau <kafai@...com>
Cc:     <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>
Subject: Re: [PATCH bpf-next v4 03/10] bpf: btf: Check members of
 struct/union

On Wed, 18 Apr 2018 11:01:15 -0700, Martin KaFai Lau wrote:
> On Wed, Apr 18, 2018 at 10:22:10AM -0700, Jakub Kicinski wrote:
> > On Tue, 17 Apr 2018 13:42:36 -0700, Martin KaFai Lau wrote:  
> > > This patch checks a few things of struct's members:
> > > 
> > > 1) It has a valid size (e.g. a "const void" is invalid)
> > > 2) A member's size (+ its member's offset) does not exceed
> > >    the containing struct's size.
> > > 3) The member's offset satisfies the alignment requirement  
> > 
> > Could we also introduce a requirement for members to have different
> > names?  Maybe it's there but I missed it.  Would BTF with duplicated
> > member names be considered valid?  
>
> It could check but I don't see BTF needs to check everything
> that clang does.

Agreed, I don't think correct tooling should ever generate duplicated
members.  Should the BTF forbid it then?  It could help catch bugs and
avoid problems.  I was thinking about JSON where duplicated field
names will result in invalid JSON potentially leading to issues in
user space stacks...