bpf: add BPF_CALL_x macros for declaring helpers
This work adds BPF_CALL_<n>() macros and converts all the eBPF helper functions
to use them, in a similar fashion like we do with SYSCALL_DEFINE<n>() macros
that are used today. Motivation for this is to hide all the register handling
and all necessary casts from the user, so that it is done automatically in the
background when adding a BPF_CALL_<n>() call.
This makes current helpers easier to review, eases to write future helpers,
avoids getting the casting mess wrong, and allows for extending all helpers at
once (f.e. build time checks, etc). It also helps detecting more easily in
code reviews that unused registers are not instrumented in the code by accident,
breaking compatibility with existing programs.
BPF_CALL_<n>() internals are quite similar to SYSCALL_DEFINE<n>() ones with some
fundamental differences, for example, for generating the actual helper function
that carries all u64 regs, we need to fill unused regs, so that we always end up
with 5 u64 regs as an argument. I reviewed all 0-5 generated BPF_CALL_<n>()
versions of the .i result and they look as expected, cross compiled on 32bit to
make sure there are no issues. All eBPF helpers are now converted to use these
macros, getting rid of a good chunk of all the nasty raw casting. Newly introduced
helpers must use them as well.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
6 files changed
