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Date:   Fri, 26 Aug 2022 14:25:50 -0700
From:   Martin KaFai Lau <kafai@fb.com>
To:     James Hilliard <james.hilliard1@gmail.com>
Cc:     bpf@vger.kernel.org, Andrii Nakryiko <andrii@kernel.org>,
        Mykola Lysenko <mykolal@fb.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Shuah Khan <shuah@kernel.org>, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] selftests/bpf: Fix bind{4,6} tcp/socket header type
 conflict
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On Fri, Aug 26, 2022 at 11:42:10AM -0600, James Hilliard wrote:
> On Fri, Aug 26, 2022 at 11:17 AM Martin KaFai Lau <kafai@fb.com> wrote:
> >
> > On Fri, Aug 26, 2022 at 12:13:54AM -0600, James Hilliard wrote:
> > > On Thu, Aug 25, 2022 at 11:49 PM Martin KaFai Lau <kafai@fb.com> wrote:
> > > >
> > > > On Thu, Aug 25, 2022 at 11:31:15PM -0600, James Hilliard wrote:
> > > > > On Thu, Aug 25, 2022 at 11:16 PM Martin KaFai Lau <kafai@fb.com> wrote:
> > > > > >
> > > > > > On Thu, Aug 25, 2022 at 04:17:49PM -0600, James Hilliard wrote:
> > > > > > > There is a potential for us to hit a type conflict when including
> > > > > > > netinet/tcp.h with sys/socket.h, we can replace both of these includes
> > > > > > > with linux/tcp.h to avoid this conflict.
> > > > > > >
> > > > > > > Fixes errors like:
> > > > > > > In file included from /usr/include/netinet/tcp.h:91,
> > > > > > >                  from progs/bind4_prog.c:10:
> > > > > > > /home/buildroot/opt/cross/lib/gcc/bpf/13.0.0/include/stdint.h:34:23: error: conflicting types for 'int8_t'; have 'char'
> > > > > > >    34 | typedef __INT8_TYPE__ int8_t;
> > > > > > >       |                       ^~~~~~
> > > > > > > In file included from /usr/include/x86_64-linux-gnu/sys/types.h:155,
> > > > > > >                  from /usr/include/x86_64-linux-gnu/bits/socket.h:29,
> > > > > > >                  from /usr/include/x86_64-linux-gnu/sys/socket.h:33,
> > > > > > >                  from progs/bind4_prog.c:9:
> > > > > > > /usr/include/x86_64-linux-gnu/bits/stdint-intn.h:24:18: note: previous declaration of 'int8_t' with type 'int8_t' {aka 'signed char'}
> > > > > > >    24 | typedef __int8_t int8_t;
> > > > > > >       |                  ^~~~~~
> > > > > > > /home/buildroot/opt/cross/lib/gcc/bpf/13.0.0/include/stdint.h:43:24: error: conflicting types for 'int64_t'; have 'long int'
> > > > > > >    43 | typedef __INT64_TYPE__ int64_t;
> > > > > > >       |                        ^~~~~~~
> > > > > > > /usr/include/x86_64-linux-gnu/bits/stdint-intn.h:27:19: note: previous declaration of 'int64_t' with type 'int64_t' {aka 'long long int'}
> > > > > > >    27 | typedef __int64_t int64_t;
> > > > > > >       |                   ^~~~~~~
> > > > > > > make: *** [Makefile:537: /home/buildroot/bpf-next/tools/testing/selftests/bpf/bpf_gcc/bind4_prog.o] Error 1
> > > > > > >
> > > > > > > Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> > > > > > > ---
> > > > > > >  tools/testing/selftests/bpf/progs/bind4_prog.c | 3 +--
> > > > > > >  tools/testing/selftests/bpf/progs/bind6_prog.c | 3 +--
> > > > > > >  2 files changed, 2 insertions(+), 4 deletions(-)
> > > > > > >
> > > > > > > diff --git a/tools/testing/selftests/bpf/progs/bind4_prog.c b/tools/testing/selftests/bpf/progs/bind4_prog.c
> > > > > > > index 474c6a62078a..6bd20042fd53 100644
> > > > > > > --- a/tools/testing/selftests/bpf/progs/bind4_prog.c
> > > > > > > +++ b/tools/testing/selftests/bpf/progs/bind4_prog.c
> > > > > > > @@ -6,8 +6,7 @@
> > > > > > >  #include <linux/bpf.h>
> > > > > > >  #include <linux/in.h>
> > > > > > >  #include <linux/in6.h>
> > > > > > > -#include <sys/socket.h>
> > > > > > > -#include <netinet/tcp.h>
> > > > > > These includes look normal to me.  What environment is hitting this.
> > > > >
> > > > > I was hitting this error with GCC 13(GCC master branch).
> > > > These two includes (<sys/socket.h> and <netinet/tcp.h>) are normal,
> > > > so does it mean all existing programs need to change to use gcc 13 ?
> > >
> > > Well I think it's mostly just an issue getting hit with GCC-BPF as it
> > > looks to me like a cross compilation host/target header conflict.
> > The users have been using these headers in the bpf progs.
> 
> Users can migrate away from libc headers over time, migrating away
imo, not without a good reason.

> shouldn't cause regressions and should improve reliability.
May be I am missing something.  I also don't understand the reliability
part.

In this sys/socket.h as an example, what is wrong in using
"'int8_t' {aka 'signed char'}" from libc and the one from
gcc "'int8_t'; have 'char'" must be used instead.

Why LLVM bpf does not have issue ?

> 
> > The solution should be on the GCC-BPF side instead of changing
> > all bpf progs.
> 
> I mean, GCC doesn't really control which libc is available, it seems to
> be a bad idea to use libc headers in general as they are developed
> separately from GCC and the kernel/libbpf.
> 
> I'm not really sure how one would fix this on the GCC-BPF side without
> introducing more potential header conflicts.