linux-kernel - Re: [PATCH bpf-next v2 2/3] bpf: btf: add btf print functionality

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Message-ID: <20180703153843.7a3425af@cakuba.netronome.com>
Date:   Tue, 3 Jul 2018 15:38:43 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Okash Khawaja <osk@...com>, Martin KaFai Lau <kafai@...com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>,
        "Quentin Monnet" <quentin.monnet@...ronome.com>,
        "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <kernel-team@...com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 2/3] bpf: btf: add btf print functionality

On Tue, 3 Jul 2018 15:23:31 -0700, Jakub Kicinski wrote:
> > > > +			else
> > > > +				jsonw_printf(jw, "%hhd", *((char *)data));    
> > > 
> > > ... I think you need to always print a string, and express it as
> > > \u00%02hhx for non-printable.    
> > Okay that makes sense  
> 
> Yeah, IDK, char can be used as a byte as well as a string.  In eBPF
> it may actually be more likely to just be used as a raw byte buffer...

Actually, what is the definition/purpose of BTF_INT_CHAR?  There seems
to be no BTF_INT_SHORT and BTF_INT_SIGNED can simply be of size 8...
Is normal int only used for bitfields of size 8 and BTF_INT_CHAR for
char variables?

The kernel seems to be rejecting combinations of those flags, is
unsigned char going to not be marked as char then?

> Either way I think it may be nice to keep it consistent, at least for
> the JSON output could we do either always ints or always characters?