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

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Mar 19, 2024 at 12:11:06PM +0100, Jiri Olsa wrote:
> 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

nah, I'll keep using __nocf_check, __noendbr is bery arch
specific as you said

jirka

> 
> > 
> > > +
> > >  /* 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