From:   Jiri Olsa <olsajiri@gmail.com>
Date:   Thu, 2 Feb 2023 12:32:33 +0100
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Jiri Olsa <olsajiri@gmail.com>, Ian Rogers <irogers@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>,
        Connor OBrien <connoro@google.com>,
        Kumar Kartikeya Dwivedi <memxor@gmail.com>,
        bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] tools/resolve_btfids: Tidy host CFLAGS forcing
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On Wed, Feb 01, 2023 at 02:21:16PM -0700, Nathan Chancellor wrote:

SNIP

> > > Should we do this and the hostprogs migration as a follow up? There
> > > isn't that much use of hostprogs in tools, but I like that your change
> > > will show HOSTCC rather than CC during compilation. If we use
> > > hostprogs can we just avoid the overrides altogether?
> > 
> > right, I think so.. we can now remove it for the BINARY target and
> > then for the rest of 'prepare' once they are converted to hostprogs..
> > not sure how 'hostprogs' will work for library, will need to check
> > 
> > I'll try to send the format patch with the fix below tomorrow
> > 
> > Nathan, any chance you could test it?
> 
> 
> Sure thing, would you happen to have a single patch file of what I
> should test? I am a little confused from reading the thread (unless what
> you want tested has not been sent yet).

I meant the change below, but I posted the formal patch now:
  https://lore.kernel.org/bpf/20230202112839.1131892-1-jolsa@kernel.org/T/#u

thanks,
jirka

> 
> Cheers,
> Nathan
> 
> > > > ---
> > > > diff --git a/tools/bpf/resolve_btfids/Build b/tools/bpf/resolve_btfids/Build
> > > > index ae82da03f9bf..077de3829c72 100644
> > > > --- a/tools/bpf/resolve_btfids/Build
> > > > +++ b/tools/bpf/resolve_btfids/Build
> > > > @@ -1,3 +1,5 @@
> > > > +hostprogs := resolve_btfids
> > > > +
> > > >  resolve_btfids-y += main.o
> > > >  resolve_btfids-y += rbtree.o
> > > >  resolve_btfids-y += zalloc.o
> > > > @@ -7,4 +9,4 @@ resolve_btfids-y += str_error_r.o
> > > >
> > > >  $(OUTPUT)%.o: ../../lib/%.c FORCE
> > > >         $(call rule_mkdir)
> > > > -       $(call if_changed_dep,cc_o_c)
> > > > +       $(call if_changed_dep,host_cc_o_c)
> > > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > > index daed388aa5d7..de513fd08535 100644
> > > > --- a/tools/bpf/resolve_btfids/Makefile
> > > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > > @@ -22,6 +22,9 @@ HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)
> > > >                   EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> > > >
> > > >  RM      ?= rm
> > > > +HOSTCC  ?= gcc
> > > > +HOSTLD  ?= ld
> > > > +HOSTAR  ?= ar
> > > >  CROSS_COMPILE =
> > > >
> > > >  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
> > > > @@ -64,7 +67,7 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
> > > >  LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> > > >  LIBELF_LIBS  := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
> > > >
> > > > -CFLAGS += -g \
> > > > +HOSTCFLAGS += -g \
> > > >            -I$(srctree)/tools/include \
> > > >            -I$(srctree)/tools/include/uapi \
> > > >            -I$(LIBBPF_INCLUDE) \
> > > > @@ -73,7 +76,7 @@ CFLAGS += -g \
> > > >
> > > >  LIBS = $(LIBELF_LIBS) -lz
> > > >
> > > > -export srctree OUTPUT CFLAGS Q
> > > > +export srctree OUTPUT HOSTCFLAGS Q HOSTCC HOSTLD HOSTAR
> > > >  include $(srctree)/tools/build/Makefile.include
> > > >
> > > >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)