Re: [PATCH bpf-next v5 07/16] bpf: Reuse MAX_BPF_FUNC_ARGS for maximum number of arguments

bot+bpf-ci
2026-04-18T00:52:41Z

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> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1151,6 +1151,10 @@ struct bpf_prog_offload {
>
> -/* The longest tracepoint has 12 args.
> +/* The longest tracepoint has 12 args.

This isn't a bug, but the multi-line comment opening doesn't follow BPF
subsystem style. Per bpf.md: 'Multi-line comments MUST have the opening
/* on its own line'. The rule applies even if surrounding code uses the
old style.

Should this be reformatted as:

/*
* The longest tracepoint has 12 args.
* See include/trace/bpf_probe.h
*
* Also reuse this macro for maximum number of arguments a BPF function
* or a kfunc can have. Args 1-5 are passed in registers, args 6-12 via
* stack arg slots.
*/

> * See include/trace/bpf_probe.h
> + *
> + * Also reuse this macro for maximum number of arguments a BPF function
> + * or a kfunc can have. Args 1-5 are passed in registers, args 6-12 via

Should this say "kfuncs" instead of "kfunc's"? The context is plural
(referring to multiple functions), not possessive.

Additionally, bot+bpf-ci@kernel.org raised a concern in v5 about the
calling convention description. The comment states "Args 1-5 are passed
in registers, args 6-12 via stack arg slots," but argument 6 is actually
passed in the R9 register, not on the stack.

Looking at arch/x86/net/bpf_jit_comp.c, the existing comment states:
"x86-64 supports up to MAX_BPF_FUNC_ARGS arguments. 1-6 are passed
through regs, the remains are through stack."

The follow-up commit 0ef907c3ec2c in this patch series documents the
actual calling convention as: "Follow x86-64 calling convention for both
BPF-to-BPF and kfunc calls: - Arg 6 is passed in the R9 register - Args
7+ are passed on the stack at [rsp]"

Should the comment say "Args 1-5 are passed in registers, arg 6 in R9
register, args 7-12 via stack arg slots" instead?

Reference: https://lore.kernel.org/bpf/d23db60b9c7e22d8ab443688b4f2da8d5594d6c07698cdc282faccaade757430@mail.kernel.org/

> + * stack arg slots.
> */
> #define MAX_BPF_FUNC_ARGS 12
>

---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/24592562564