[Bug bpf/23829] Bug introduced in bpf -base.cxx in git master

["me at serhei dot io" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=23829

--- Comment #6 from Serhei Makarov <me at serhei dot io> ---
Thanks for that info. I've tested with bpf.h from kernel 4.8. Other defines
aside from __BPF_FUNC_MAPPER and BPF_J{LT,LE,SLT,SLE} seem to be present.

The build errors reported should be fixed in commits 3d9e0d2a5 (for _F format
specifiers on 32-bit systems) and 8fb0cb4a (for undefined bpf.h symbols).
Partly fixed by adding a fallback version of __BPF_FUNC_MAPPER and fallback
defines for the new BPF_J(...) insn opcodes (these are recognized by the new
embedded-code assembler; stapbpf backend already replaces these with older
insns, so the code should work even on old kernel versions that do not support
them).

Let me know if the fixes work and I can close the bug, or if I need to refine
my workaround further.

This exposes a deeper issue, in that SystemTap/BPF must be compiled against a
recent kernel version to generate modules that use BPF features from that
version. This has also caused hiccups e.g. when building SystemTap RPM packages
in mockbuild on a kernel without eBPF support. Don't see an obvious workaround
for this.

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