Re: [PATCH bpf-next] tools/resolve_btfids: Compile resolve_btfids as host program

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Feb 02, 2023 at 12:14:14PM -0800, Ian Rogers wrote:
> On Thu, Feb 2, 2023 at 9:21 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > On Thu, Feb 02, 2023 at 12:28:39PM +0100, Jiri Olsa wrote:
> > > Making resolve_btfids to be compiled as host program so
> > > we can avoid cross compile issues as reported by Nathan.
> > >
> > > Also we no longer need HOST_OVERRIDES for BINARY target,
> > > just for 'prepare' targets.
> > >
> > > Cc: Ian Rogers <irogers@google.com>
> > > Fixes: 13e07691a16f ("tools/resolve_btfids: Alter how HOSTCC is forced")
> > > Reported-by: Nathan Chancellor <nathan@kernel.org>
> > > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> >
> > Tested-by: Nathan Chancellor <nathan@kernel.org>
> >
> 
> This change has my,
> Acked-by: Ian Rogers <irogers@google.com>

thanks

> but I wonder about cleaning HOST_OVERRIDES. From the patch I sent,
> would it be worth adding:
> ```
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -17,9 +17,9 @@ else
>   MAKEFLAGS=--no-print-directory
> endif
> 
> -# always use the host compiler
> +# Overrides for the prepare step libraries.
> HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)"
> ARCH="$(HOSTARCH)" \
> -                 EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> +                 CROSS_COMPILE=""
> 
> RM      ?= rm
> HOSTCC  ?= gcc
> ```
> It seems odd passing HOSTCFLAGS this way and mixing HOSTCC as CC with
> CROSS_COMPILE set seems open to failure. Perhaps we should just get
> rid of this, add something like a HOST=1 option for building the
> library and then in the library code do the right thing. That would
> fix the issue that libsubcmd and libbpf here are being built reporting
> CC rather than HOSTCC, make the build flags in general more sane.

could you send separate patch with that?

also I'll try to check if we could make prepare libs as hostprogs,
because I think the changes you suggest might depend on that

jirka

> 
> Thanks,
> Ian
> 
> > > ---
> > >  tools/bpf/resolve_btfids/Build    | 4 +++-
> > >  tools/bpf/resolve_btfids/Makefile | 9 ++++++---
> > >  2 files changed, 9 insertions(+), 4 deletions(-)
> > >
> > > 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)
> > > +     $(call if_changed_dep,host_cc_o_c)
> > > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > > index daed388aa5d7..abdd68ac08f4 100644
> > > --- a/tools/bpf/resolve_btfids/Makefile
> > > +++ b/tools/bpf/resolve_btfids/Makefile
> > > @@ -22,6 +22,9 @@ HOST_OVERRIDES := AR="$(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) \
> > > @@ -73,11 +76,11 @@ 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)
> > > -     $(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> > > +     $(Q)$(MAKE) $(build)=resolve_btfids
> > >
> > >  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
> > >       $(call msg,LINK,$@)
> > > --
> > > 2.39.1
> > >