Re: [PATCH v4 bpf-next 6/9] selftests/bpf: Test gen_prologue and gen_epilogue

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2024-08-27 at 12:48 -0700, Martin KaFai Lau wrote:
> From: Martin KaFai Lau <martin.lau@kernel.org>
> 
> This test adds a new struct_ops "bpf_testmod_st_ops" in bpf_testmod.
> The ops of the bpf_testmod_st_ops is triggered by new kfunc calls
> "bpf_kfunc_st_ops_test_*logue". These new kfunc calls are
> primarily used by the SEC("syscall") program. The test triggering
> sequence is like:
>     SEC("syscall")
>     syscall_prologue_subprog(struct st_ops_args *args)
>         bpf_kfunc_st_op_test_prologue(args)
> 	    st_ops->test_prologue(args)
> 
> .gen_prologue adds 1000 to args->a
> .gen_epilogue adds 10000 to args->a
> .gen_epilogue will also set the r0 to 2 * args->a.
> 
> The .gen_prologue and .gen_epilogue of the bpf_testmod_st_ops
> will test the prog->aux->attach_func_name to decide if
> it needs to generate codes.
> 
> The main programs of the pro_epilogue_subprog.c will call a subprog()
> which does "args->a += 1".
> 
> The main programs of the pro_epilogue_kfunc.c will call a
> new kfunc bpf_kfunc_st_ops_inc10 which does "args->a += 10".
> 
> This patch uses the test_loader infra to check the __xlated
> instructions patched after gen_prologue and/or gen_epilogue.
> The __xlated check is based on Eduard's example (Thanks!) in v1.
> 
> args->a is returned by the struct_ops prog (either the main prog
> or the epilogue). Thus, the __retval of the SEC("syscall") prog
> is checked. For example, when triggering the ops in the
> 'SEC("struct_ops/test_epilogue_subprog") int test_epilogue_subprog'
> The expected args->a is +1 (subprog call) + 10000 (.gen_epilogue) = 10001.
> The expected return value is 2 * 10001 (.gen_epilogue).
> 
> Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]

> diff --git a/tools/testing/selftests/bpf/progs/pro_epilogue_kfunc.c b/tools/testing/selftests/bpf/progs/pro_epilogue_kfunc.c
> new file mode 100644
> index 000000000000..7d1124cf4942
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/pro_epilogue_kfunc.c
> @@ -0,0 +1,156 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
> +
> +#include <vmlinux.h>
> +#include <bpf/bpf_tracing.h>
> +#include "bpf_misc.h"
> +#include "../bpf_testmod/bpf_testmod.h"
> +#include "../bpf_testmod/bpf_testmod_kfunc.h"
> +
> +char _license[] SEC("license") = "GPL";
> +
> +void __kfunc_btf_root(void)
> +{
> +	struct st_ops_args args = {};
> +
> +	bpf_kfunc_st_ops_inc10(&args);

Nit: 'bpf_kfunc_st_ops_inc10(0);' would also work.

> +}

As a side note, I think that kfunc and subprog sets of tests could be
combined in order to have less code. Probably does not matter.

[...]