Hello,
this is the v2 of the many args series for arm64, being itself a revival of Xu Kuhoai's work to enable larger arguments count for BPF programs on ARM64 ([1]).
The discussions in v1 shed some light on some issues around specific cases, for example with functions passing struct on stack with custom packing/alignment attributes: those cases can not be properly detected with the current BTF info. So this new revision aims to separate concerns with a simpler implementation, just accepting additional args on stack if we can make sure about the alignment constraints (and so, refusing attachment to functions passing structs on stacks). I then checked if the specific alignment constraints could be checked with larger scalar types rather than structs, but it appears that this use case is in fact rejected at the verifier level (see a9b59159d338 ("bpf: Do not allow btf_ctx_access with __int128 types")). So in the end the specific alignment corner cases raised in [1] can not really happen in the kernel in its current state. This new revision still brings support for the standard cases as a first step, it will then be possible to iterate on top of it to add the more specific cases like struct passed on stack and larger types.
[1] https://lore.kernel.org/all/20230917150752.69612-1-xukuohai@huaweicloud.com/...
Signed-off-by: Alexis Lothoré (eBPF Foundation) alexis.lothore@bootlin.com --- Changes in v2: - remove alignment computation from btf.c - deduce alignment constraints directly in jit compiler for simple types - deny attachment to functions with "corner-cases" arguments (ie: structs on stack) - remove custom tests, as the corresponding use cases are locked either by the JIT comp or the verifier - drop RFC - Link to v1: https://lore.kernel.org/r/20250411-many_args_arm64-v1-0-0a32fe72339e@bootlin...
--- Alexis Lothoré (eBPF Foundation) (1): selftests/bpf: enable many-args tests for arm64
Xu Kuohai (1): bpf, arm64: Support up to 12 function arguments
arch/arm64/net/bpf_jit_comp.c | 234 ++++++++++++++++++++------- tools/testing/selftests/bpf/DENYLIST.aarch64 | 2 - 2 files changed, 180 insertions(+), 56 deletions(-) --- base-commit: 9435138c069117cd59a4912b5ea2ae44cc2c5ffa change-id: 20250220-many_args_arm64-8bd3747e6948
Best regards,