Re: [PATCHv3 bpf-next 2/2] bpf: Move bpf_dispatcher function out of ftrace locations

Jiri Olsa
2022-09-06T10:08:07Z

On Mon, Sep 05, 2022 at 11:23:45AM -0400, Steven Rostedt wrote:
> On Sat, 3 Sep 2022 15:11:54 +0200
> Jiri Olsa <jolsa@kernel.org> wrote:
>
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index f9920f1341c8..089c20cefd2b 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -284,6 +284,7 @@ config X86
> > select PROC_PID_ARCH_STATUS if PROC_FS
> > select HAVE_ARCH_NODE_DEV_GROUP if X86_SGX
> > imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI
> > + select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE
> >
> > config INSTRUCTION_DECODER
> > def_bool y
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 9c1674973e03..e267625557cb 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -924,7 +924,14 @@ int arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs);
> > }, \
> > }
> >
> > +#ifdef CONFIG_X86_64
>
> I think Peter may have already mentioned this, but shouldn't he above be:
>
> #ifdef HAVE_DYNAMIC_FTRACE_NO_PATCHABLE

different archs need different patchable_function_entry(X) attribute
so I think we should use arch configs in here

also having HAVE_DYNAMIC_FTRACE_NO_PATCHABLE option enabled does not
imply there's support for dispatcher image generation, so we might
endup with extra nop bytes

jirka

>
> ??
>
> -- Steve
>
> > +#define BPF_DISPATCHER_ATTRIBUTES __attribute__((patchable_function_entry(5)))
> > +#else
> > +#define BPF_DISPATCHER_ATTRIBUTES
> > +#endif
> > +
> > #define DEFINE_BPF_DISPATCHER(name) \
> > + notrace BPF_DISPATCHER_ATTRIBUTES \
> > noinline __nocfi unsigned int bpf_dispatcher_##name##_func( \
> > const void *ctx, \
> > const struct bpf_insn *insnsi, \
> > --