[DTrace-devel] [PATCH 1/2] config: add rule to check gcc option

[Kris Van Hees]

Per conversations about this, I'm going with the option to rename this to be
BPF-specific (check-bpfc-option-rule).  If and when we need a more generic
form of this, we can either expand this to add a new rule for a more generic
case.

On Thu, Feb 22, 2024 at 04:03:24PM +0000, Nick Alcock wrote:
> On 22 Feb 2024, Kris Van Hees via DTrace-devel stated:
> 
> > Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> 
> I was just wondering if it was time to add something like this!
> 
> > ---
> >  Makeconfig | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >
> > diff --git a/Makeconfig b/Makeconfig
> > index 0f7c4364..332e9519 100644
> > --- a/Makeconfig
> > +++ b/Makeconfig
> > @@ -163,6 +163,39 @@ $(CONFIG_H): $(objdir)/.config/config.$(1).h
> >  $(CONFIG_MK): $(objdir)/.config/config.$(1).mk
> >  endef
> >  
> > +# Generate a makefile rule to check for support for  OPTION in gcc and emit an
> > +# appropriate header file fragment into a file under $(objdir)/.config.
> > +#
> > +# The first argument must be suitable for a filename fragment, for a makefile
> > +# rule name and for a #define.
> > +#
> > +# Syntax: $(call check-gcc-option-rule,name,option)
> > +define check-gcc-option-rule
> > +$(objdir)/.config/config.$(1).h $(objdir)/.config/config.$(1).mk: $(objdir)/.config/.dir.stamp
> > +	case x$(HAVE_$(1)) in \
> > +	xyes) echo '#define HAVE_$(1) 1' > $(objdir)/.config/config.$(1).h; \
> > +	     echo 'HAVE_$(1)=y' > $(objdir)/.config/config.$(1).mk;; \
> > +	xno) echo '/* #undef HAVE_$(1) */' > $(objdir)/.config/config.$(1).h; \
> > +	     echo '# HAVE_$(1) undefined' > $(objdir)/.config/config.$(1).mk;; \
> > +	*) if $(BPFC) --help $(2) 2>&1 >/dev/null | grep error; then \
> 
> This only works for options that do not take arguments and don't produce
> errors for other reasons when specified alone. e.g.
> 
> compiler at loom 503 /usr/src/llvm/llvm/lldb% gcc --help -o 2>&1 | grep error:
> gcc: error: missing filename after ???-o???
> 
> Maybe that's good enough, I don't know. In general it's probably better
> to try to add the option to $(CC) $(CFLAGS) and try to compile
> something, like the other tests do, since a lot of options are only
> valid when actually compiling or are only considered valid for
> particular frontends (and GCC doesn't know what frontend it's using
> unless you specify it with -x c or whatever). So at the very least using
> -x c would probably be a good idea.
> 
> More generally, this is misnamed: it's not checking a GCC option, it's
> checking for a *BPFC* option. This is probably best fixed by adding
> another parameter which is the compiler to use, so we can pass in either
> $(BPFC) or $(CC).
> 
> -- 
> NULL && (void)