Re: [PATCH] selftests/bpf: Fix bind{4,6} tcp/socket header type conflict

["Jose E. Marchesi" <jose.marchesi@oracle.com>]

> 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.

This is an interesting issue.

Right now the BPF GCC target is a sort of a bare-metal target.  As such,
it provides a set of header files that implement ISO C types and other
machinery (i.e. it doesn't rely on a C library to provide them):

  iso646.h
  stdalign.h
  stdarg.h
  stdatomic.h
  stdbool.h
  stddef.h
  stdfix.h
  stdint.h
  stdnoreturn.h
  tgmath.h
  unwind.h
  varargs.h

This is because we were expecting this to be used like:

       <compiler-provided std C headers>
                  |        |
                  v        |
        <kernel headers>   |
                  |        |
                  v        v
               <BPF C program>

However, if it is expected/intended for C BPF programs to include libc
headers, such as sys/socket.h, this can quickly go sour as you have
found with that conflict.

So this leads to the question: should we turn the BPF target into a
target that assumes a libc?  This basically means we will be assuming
BPF programs are always compiled in an environment that provides a
standard stdint.h, stdbool.h and friends.

Thoughts?

>> > > I don't prefer the selftest writers need to remember this rule.
>> > >
>> > > Beside, afaict, tcp.h should be removed because
>> > > I don't see this test needs it.  I tried removing it
>> > > and it works fine.  It should be removed instead of replacing it
>> > > with another unnecessary tcp.h.
>> >
>> > Oh, that does also appear to work, thought I had tried that already but I guess
>> > I hadn't, sent a v2 with them removed:
>> > https://lore.kernel.org/bpf/20220826052925.980431-1-james.hilliard1@gmail.com/T/#u
>> >
>> > >
>> > > > +#include <linux/tcp.h>
>> > > >  #include <linux/if.h>
>> > > >  #include <errno.h>
>> > > >
>> > > > diff --git a/tools/testing/selftests/bpf/progs/bind6_prog.c
>> > > > b/tools/testing/selftests/bpf/progs/bind6_prog.c
>> > > > index c19cfa869f30..f37617b35a55 100644
>> > > > --- a/tools/testing/selftests/bpf/progs/bind6_prog.c
>> > > > +++ b/tools/testing/selftests/bpf/progs/bind6_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>
>> > > > +#include <linux/tcp.h>
>> > > >  #include <linux/if.h>
>> > > >  #include <errno.h>
>> > > >
>> > > > --
>> > > > 2.34.1
>> > > >