On Mon, Dec 30, 2024 at 12:11 PM Ihor Solodrai via Gcc <gcc@xxxxxxxxxxx> wrote:
>
> Hello everyone.
>
> I picked up the work adding GCC BPF backend to BPF CI pipeline [1],
> originally done by Cupertino Miranda [2].
>
> I encountered issues compiling BPF objects for selftests/bpf with
> recent GCC 15 snapshots. An additional test runner binary is supposed
> to be generated by tools/testing/selftests/bpf/Makefile if BPF_GCC is
> set to a directory with GCC binaries for BPF backend. The runner
> binary depends on BPF binaries, which are produced by GCC.
>
> The first issue is compilation errors on vmlinux.h:
>
> In file included from progs/linked_maps1.c:4:
> /ci/workspace/tools/testing/selftests/bpf/tools/include/vmlinux.h:8483:9: error: expected identifier before ‘false’
> 8483 | false = 0,
> | ^~~~~
>
> A snippet from vmlinux.h:
>
> enum {
> false = 0,
> true = 1,
> };
>
> And:
>
> /ci/workspace/tools/testing/selftests/bpf/tools/include/vmlinux.h:23539:15: error: two or more data types in declaration specifiers
> 23539 | typedef _Bool bool;
> | ^~~~
>
> Full log at [3], and also at [4].
These are simple, the selftests/bpf programs need to compile with
-std=gnu17 or -std=gnu11 since GCC has changed the default to C23
which defines false and bool as keywords now and can't be redeclared
like before.
Thanks,
Andrew Pinski
>
> You can easily reproduce the errors with a dummy program:
>
> #include "vmlinux.h"
>
> int main() {
> return 0;
> }
>
> The vmlinux.h is generated from BTF, produced by pahole v1.28 from
> DWARF data contained in the vmlinux binary. The vmlinux binary I used
> in these experiments is v6.12 (adc218676eef) compiled with gcc 13.3.0
> (default Ubuntu installation).
>
> You can download the specific vmlinux.h I tried using a link below [5].
>
> I bisected recent GCC snapshots and determined that the errors related
> to the bool declarations started happening on GCC 15-20241117.
>
> 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;
> | ^~~~~~~
>
> This is on a typical ubuntu:noble system:
>
> $ dpkg -s libc6 | grep Version
> Version: 2.39-0ubuntu8.3
>
> I got this with snapshots 15-20241110 and 15-20240922 (the oldest I
> tested). This problem may or may not be present in the most recent
> versions, I can't tell for sure.
>
> GCC team, please investigate and let me know if you're aware of
> workarounds or if there is a specific GCC version that you know is
> capable of building BPF programs in selftests/bpf.
>
> If you suspect something might be wrong with the includes for BPF
> programs, or GCC snapshot build etc, please also let me know. I mostly
> relied on Cupertino scripts when setting that up, and assumed the
> selftests/bpf/Makefile is handling BPF_GCC correctly.
>
> Thank you, and happy holidays!
>
> [1] https://github.com/libbpf/ci/pull/164
> [2] https://github.com/libbpf/ci/pull/144
> [3] https://gist.github.com/theihor/98883c4266b3489cee69e5d5aa532e79
> [4] https://github.com/libbpf/ci/actions/runs/12522053128/job/34929897322
> [5] https://gist.github.com/theihor/785bb250dd1cce3612e70b5f6d258401
> [6] https://gist.github.com/theihor/a8aa7201b30ac6b48df77bb1ea3ec0b2
>
>
