selftests/bpf: Test trampoline args around a 16-byte aligned stack arg

Add two bpf_testmod functions whose 16-byte aligned argument, a struct
holding an __int128, is passed on the stack after a hole:

  - bpf_testmod_test_int128_stack(): seven u64s before the struct, so it
    leaves a register empty on arm64 and a stack slot empty on x86-64.
  - bpf_testmod_test_int128_backfill(): a 16-byte struct of two longs
    moves to the x86-64 stack and gives R9 back to the next argument; the
    struct then leaves a stack slot empty on both x86-64 and arm64.

The __int128 is wrapped in a struct because btf_ctx_access() refuses a
program reading an integer argument wider than eight bytes, while it
lets the program read each slot of a struct argument.

The fentry programs read each argument slot from ctx[] and check that
the trampoline packs them in the BPF convention, and the fexit programs
check the return value, weighted by argument slot, which is only right
if the original function got its arguments back where its convention
wants them.

Without the preceding x86 fix the test fails with:

  test_int128_args:FAIL:s:h.lo unexpected s:h.lo: actual 2 != expected 8
  ...
  test_int128_args:FAIL:s ret unexpected s ret: actual 285 != expected 385

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261016183110.1135597-1-yonghong.song@linux.dev

0 files changed, 0 insertions, 0 deletions