Re: [PATCH v7 bpf-next 12/12] selftests/bpf: add C-level selftests for indirect jumps

[Anton Protopopov <a.s.protopopov@gmail.com>]

On 25/10/27 04:25PM, Eduard Zingerman wrote:
> On Sun, 2025-10-26 at 19:27 +0000, Anton Protopopov wrote:
> > Add C-level selftests for indirect jumps to validate LLVM and libbpf
> > functionality. The tests are intentionally disabled, to be run
> > locally by developers, but will not make the CI red.
> > 
> > Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
> > ---
> 
> [...]
> 
> > diff --git a/tools/testing/selftests/bpf/progs/bpf_gotox.c b/tools/testing/selftests/bpf/progs/bpf_gotox.c
> > new file mode 100644
> > index 000000000000..3c8ee363bda1
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/bpf_gotox.c
> > @@ -0,0 +1,402 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include "vmlinux.h"
> > +#include <bpf/bpf_helpers.h>
> > +#include <bpf/bpf_tracing.h>
> > +#include <bpf/bpf_core_read.h>
> > +#include "bpf_misc.h"
> > +
> > +/* Disable tests for now, as CI runs with LLVM-20 */
> > +#if 0
> 
> Yonghong,
> 
> I think we need the following thing in LLVM:
> 
>   diff --git a/clang/lib/Basic/Targets/BPF.cpp b/clang/lib/Basic/Targets/BPF.cpp
>   index 0411bcca5178..8de1083d758c 100644
>   --- a/clang/lib/Basic/Targets/BPF.cpp
>   +++ b/clang/lib/Basic/Targets/BPF.cpp
>   @@ -75,6 +75,7 @@ void BPFTargetInfo::getTargetDefines(const LangOptions &Opts,
>        Builder.defineMacro("__BPF_FEATURE_GOTOL");
>        Builder.defineMacro("__BPF_FEATURE_ST");
>        Builder.defineMacro("__BPF_FEATURE_LOAD_ACQ_STORE_REL");
>   +    Builder.defineMacro("__BPF_FEATURE_GOTOX");
>      }
>    }
> 
> Then, Anton will be able to use it in order to decide if to skip the
> tests, wdyt?

This will definitely be useful for the BPF side.

Where this doesn't apply is the corresponding prog_tests/bpf_gotox.c,
as it can be compiled independently and for sure it will not have
__BPF_FEATURE_GOTOX enabled. So what is the way to tell preprocessor
if gotox was enabled in BPF program? Is there a way to pass/generate
a macro definition from BPF prog to skeleton? If so, then it can be
used in the prog_tests/bpf_gotox.c to enable/disable tests.

> > +__u64 in_user;
> > +__u64 ret_user;
> > +
> > +struct simple_ctx {
> > +	__u64 x;
> > +};
> > +
> > +__u64 some_var;
> > +
> > +/*
> > + * This function adds code which will be replaced by a different
> > + * number of instructions by the verifier. This adds additional
> > + * stress on testing the insn_array maps corresponding to indirect jumps.
> > + */
> > +static __always_inline void adjust_insns(__u64 x)
> > +{
> > +	some_var ^= x + bpf_jiffies64();
> > +}
> > +
> > +SEC("syscall")
> > +int simple_test(struct simple_ctx *ctx)
> > +{
> > +	switch (ctx->x) {
> > +	case 0:
> > +		adjust_insns(ctx->x + 1);
> > +		ret_user = 2;
> > +		break;
> 
> [...]