With commit dacbfc167808 ("crypto: af_alg - Annotate struct af_alg_iv
with __counted_by"), two selftests, test_tag and crypto_sanity, now
indirectly rely on the __counted_by macro. On systems with commit
dacbfc167808 in the installed UAPI headers, the selftests build fails
with:

  In file included from tools/testing/selftests/bpf/prog_tests/crypto_sanity.c:7:
  /usr/include/linux/if_alg.h:45:22: error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’ before ‘__counted_by’
     45 |         __u8    iv[] __counted_by(ivlen);
        |                      ^~~~~~~~~~~~

This patch fixes it by regenerating stddef.h in tools/include using the
instructions from commit a778f5d46b62 ("tools/headers: Pull in stddef.h
to uapi to fix BPF selftests build in CI").

Fixes: dacbfc167808 ("crypto: af_alg - Annotate struct af_alg_iv with __counted_by")
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/8da8ef16055aa452d940668ed5359ce54adc6b0b.1777715500.git.paul.chaignon@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

For the most part of the C++ history, it couldn't have type
declarations inside anonymous unions for different reasons. At the
same time, __struct_group() relies on the latters, so when the @TAG
argument is not empty, C++ code doesn't want to build (even under
`extern "C"`):

../linux/include/uapi/linux/pkt_cls.h:25:24: error:
'struct tc_u32_sel::<unnamed union>::tc_u32_sel_hdr,' invalid;
an anonymous union may only have public non-static data members
[-fpermissive]

The safest way to fix this without trying to switch standards (which
is impossible in UAPI anyway) etc., is to disable tag declaration
for that language. This won't break anything since for now it's not
buildable at all.
Use a separate definition for __struct_group() when __cplusplus is
defined to mitigate the error, including the version from tools/.

Fixes: 50d7bd38c3aa ("stddef: Introduce struct_group() helper macro")
Reported-by: Christopher Ferris <cferris@google.com>
Closes: https://lore.kernel.org/linux-hardening/Z1HZpe3WE5As8UAz@google.com
Suggested-by: Kees Cook <kees@kernel.org> # __struct_group_tag()
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20241219135734.2130002-1-aleksander.lobakin@intel.com
Signed-off-by: Kees Cook <kees@kernel.org>

With recent sync of linux/in.h tools/include headers are now relying on
__DECLARE_FLEX_ARRAY macro, which isn't itself defined inside
tools/include headers anywhere and is instead assumed to be present in
system-wide UAPI header. This breaks isolated environments that don't
have kernel UAPI headers installed system-wide, like BPF CI ([0]).

To fix this, bring in include/uapi/linux/stddef.h into tools/include.
We can't just copy/paste it, though, it has to be processed with
scripts/headers_install.sh, which has a dependency on scripts/unifdef.
So the full command to (re-)generate stddef.h for inclusion into
tools/include directory is:

  $ make scripts_unifdef && \
    cp $KBUILD_OUTPUT/scripts/unifdef scripts/ && \
    scripts/headers_install.sh include/uapi/linux/stddef.h tools/include/uapi/linux/stddef.h

This assumes KBUILD_OUTPUT envvar is set and used for out-of-tree builds.

  [0] https://github.com/kernel-patches/bpf/actions/runs/3379432493/jobs/5610982609

Fixes: 036b8f5b8970 ("tools headers uapi: Update linux/in.h copy")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/bpf/20221102182517.2675301-2-andrii@kernel.org