netdev - Re: [PATCH 03/11] bpf: Add btf

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Message-ID: <20200619131631.GE2465907@krava>
Date:   Fri, 19 Jun 2020 15:16:31 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Wenbo Zhang <ethercflow@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Andrii Nakryiko <andriin@...com>,
        Brendan Gregg <bgregg@...flix.com>,
        Florent Revest <revest@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 03/11] bpf: Add btf_ids object

On Thu, Jun 18, 2020 at 06:06:49PM -0700, Andrii Nakryiko wrote:

SNIP

> > > +/*
> > > + * The BTF_ID_LIST macro defines pure (unsorted) list
> > > + * of BTF IDs, with following layout:
> > > + *
> > > + * BTF_ID_LIST(list1)
> > > + * BTF_ID(type1, name1)
> > > + * BTF_ID(type2, name2)
> > > + *
> > > + * list1:
> > > + * __BTF_ID__type1__name1__1:
> > > + * .zero 4
> > > + * __BTF_ID__type2__name2__2:
> > > + * .zero 4
> > > + *
> > > + */
> > > +#define BTF_ID_LIST(name)                              \
> >
> > nit: btw, you call it a list here, but btfids tool talks about
> > "sorts". Maybe stick to consistent naming. Either "list" or "set"
> > seems to be appropriate. Set implies a sorted aspect a bit more, IMO.

so how about we keep BTF_ID_LIST as it is and rename
BTF_WHITELIST_* to BTF_SET_*

> >
> > > +asm(                                                   \
> > > +".pushsection " SECTION ",\"a\";               \n"     \
> > > +".global " #name ";                            \n"     \
> >
> > I was expecting to see reserved 4 bytes for list size? I also couldn't
> > find where btfids tool prepends it. From what I could understand, it
> > just assumed the first 4 bytes are the length prefix? Sorry if I'm
> > slow...
> 
> Never mind, this is different from whitelisting you do in patch #8.
> But now I'm curious how this list symbol gets its size correctly
> calculated?..

so the BTF_ID_LIST list does not care about the size,
each symbol in the 'list' gets resolved based on its
__BTF_ID__XX__symbol__XX symbol

the count is kept in BTF_WHITELIST_* list because we
need it to sort it and search in it

thanks,
jirka