Re: [PATCH RFC bpf-next 3/3] selftests/bpf: Mark uprobe trigger functions with nocf_check attribute

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Mar 18, 2024 at 06:22:02PM -0700, Andrii Nakryiko wrote:
> On Mon, Mar 18, 2024 at 2:32 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Some distros seem to enable the -fcf-protection=branch by default,
> > which breaks our setup on first instruction of uprobe trigger
> > functions and place there endbr64 instruction.
> >
> > Marking them with nocf_check attribute to skip that.
> >
> > Adding -Wno-attributes for bench objects, becase nocf_check can
> > be used only when -fcf-protection=branch is enabled, otherwise
> > we get a warning and break compilation.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  tools/include/linux/compiler.h                     | 4 ++++
> >  tools/testing/selftests/bpf/Makefile               | 2 +-
> >  tools/testing/selftests/bpf/benchs/bench_trigger.c | 6 +++---
> >  3 files changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
> > index 7b65566f3e42..14038ce04ca4 100644
> > --- a/tools/include/linux/compiler.h
> > +++ b/tools/include/linux/compiler.h
> > @@ -58,6 +58,10 @@
> >  #define noinline
> >  #endif
> >
> > +#ifndef __nocfcheck
> > +#define __nocfcheck __attribute__((nocf_check))
> > +#endif
> 
> Let's preserve spelling of the attribut, __nocf_check ?
> 
> BTW, just FYI, seems like kernel is defining it as:
> 
> #define __noendbr    __attribute__((nocf_check))
> 
> Thought somewhere deep in x86-specific code, so probably not a good
> idea to use it here?

ugh, I missed it.. better to use __noendbr

> 
> > +
> >  /* Are two types/vars the same type (ignoring qualifiers)? */
> >  #ifndef __same_type
> >  # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
> > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> > index e425a946276b..506d3d592093 100644
> > --- a/tools/testing/selftests/bpf/Makefile
> > +++ b/tools/testing/selftests/bpf/Makefile
> > @@ -726,7 +726,7 @@ $(OUTPUT)/test_cpp: test_cpp.cpp $(OUTPUT)/test_core_extern.skel.h $(BPFOBJ)
> >  # Benchmark runner
> >  $(OUTPUT)/bench_%.o: benchs/bench_%.c bench.h $(BPFOBJ)
> >         $(call msg,CC,,$@)
> > -       $(Q)$(CC) $(CFLAGS) -O2 -c $(filter %.c,$^) $(LDLIBS) -o $@
> > +       $(Q)$(CC) $(CFLAGS) -O2 -Wno-attributes -c $(filter %.c,$^) $(LDLIBS) -o $@
> 
> let's better use `#pragma warning disable` in relevant .c files,
> instead of this global flag?

ok, will try that

thanks,
jirka