On Thursday, January 2nd, 2025 at 1:47 AM, Jose E. Marchesi
<[email protected]> wrote:
> Hi Ihor.
> Thanks for working on this! :)
>
> > [...]
> > Older versions compile the dummy program without errors, however on
> > attempt to build the selftests there is a different issue: conflicting
> > int64 definitions (full log at [6]).
> >
> > 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 /usr/include/linux/if.h:28,
> > from /usr/include/linux/icmp.h:23,
> > from progs/test_cls_redirect_dynptr.c:10:
> > /usr/include/x86_64-linux-gnu/bits/stdint-intn.h:27:19: error: conflicting
> > types for ‘int64_t’; have ‘__int64_t’ {aka ‘long long int’}
> > 27 | typedef __int64_t int64_t;
> > | ^~~~~~~
> > In file included from progs/test_cls_redirect_dynptr.c:6:
> > /ci/workspace/bpfgcc.20240922/lib/gcc/bpf-unknown-none/15.0.0/include/stdint.h:43:24:
> > note: previous declaration of ‘int64_t’ with type ‘int64_t’ {aka ‘long
> > int’}
> > 43 | typedef INT64_TYPE int64_t;
> > | ^~~~~~~
>
>
> I think this is what is going on:
>
> The BPF selftest is indirectly including glibc headers from the host
> where it is being compiled. In this case your x86_64 ubuntu system.
>
> Many glibc headers include bits/wordsize.h, which in the case of x86_64
> is:
>
> #if defined x86_64 && !defined ILP32
> # define __WORDSIZE 64
> #else
> # define __WORDSIZE 32
> #define __WORDSIZE32_SIZE_ULONG 0
> #define __WORDSIZE32_PTRDIFF_LONG 0
> #endif
>
> and then in bits/types.h:
>
> #if __WORDSIZE == 64
> typedef signed long int __int64_t;
> typedef unsigned long int __uint64_t;
> #else
> extension typedef signed long long int __int64_t;
> extension typedef unsigned long long int __uint64_t;
> #endif
>
> i.e. your BPF program ends using __WORDSIZE 32. This eventually leads
> to int64_t being defined as `signed long long int' in stdint-intn.h, as
> it would correspond to a x86_64 program running in 32-bit mode.
>
> GCC BPF, on the other hand, is a "baremetal" compiler and it provides a
> small set of headers (including stdint.h) that implement standard C99
> types like int64_t, adjusted to the BPF architecture.
>
> In this case there is a conflict between the 32-bit x86_64 definition of
> int64_t and the one of BPF.
Hi Jose, thanks for breaking this down.
I was able to mitigate int64_t declaration conflict by passing
-nostdinc to gcc.
Currently system-installed headers are being passed via -idirafter in
a compilation command:
/ci/workspace/bpfgcc.20241229/bin/bpf-unknown-none-gcc \
-g -Wall -Werror -D__TARGET_ARCH_x86 -mlittle-endian \
-I/ci/workspace/tools/testing/selftests/bpf/tools/include
-I/ci/workspace/tools/testing/selftests/bpf \
-I/ci/workspace/tools/include/uapi \
-I/ci/workspace/tools/testing/selftests/usr/include \
-Wno-compare-distinct-pointer-types \
-idirafter /usr/lib/gcc/x86_64-linux-gnu/13/include \
-idirafter /usr/local/include \
-idirafter /usr/include/x86_64-linux-gnu \
-idirafter /usr/include \
-DBPF_NO_PRESERVE_ACCESS_INDEX \
-Wno-attributes \
-O2 -std=gnu17 \ # -nostdinc here helps
-c progs/test_cls_redirect.c \
-o
/ci/workspace/tools/testing/selftests/bpf/bpf_gcc/test_cls_redirect.bpf.o
Passing -nostdinc makes gcc to pick compiler-installed header, if I
understand correctly.
>
> PS: the other headers installed by GCC BPF are:
> float.h iso646.h limits.h stdalign.h stdarg.h stdatomic.h stdbool.h
> stdckdint.h stddef.h stdfix.h stdint.h stdnoreturn.h syslimits.h
> tgmath.h unwind.h varargs.h
>From your comments, it seems that BPF programs *must not* include
system glibc headers when compiled with GCC. Or is this only true for
the headers you listed above?
I wonder what is the proper way to build BPF programs with gcc then.
In the source code the includes are what you'd expect:
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h> // conflict is between this
#include <string.h>
#include <linux/bpf.h>
#include <linux/icmp.h> // and this
#include <linux/icmpv6.h>
...
Any suggestions?
Thanks.
