Re: [PATCH bpf-next] tools/resolve_btfids: fix setting HOSTCFLAGS

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, May 31, 2023 at 09:20:44AM +0200, Viktor Malik wrote:
> On 5/30/23 15:29, Jiri Olsa wrote:
> > On Tue, May 30, 2023 at 02:33:52PM +0200, Viktor Malik wrote:
> >> Building BPF selftests with custom HOSTCFLAGS yields an error:
> >>
> >>     # make HOSTCFLAGS="-O2"
> >>     [...]
> >>       HOSTCC  ./tools/testing/selftests/bpf/tools/build/resolve_btfids/main.o
> >>     main.c:73:10: fatal error: linux/rbtree.h: No such file or directory
> >>        73 | #include <linux/rbtree.h>
> >>           |          ^~~~~~~~~~~~~~~~
> >>
> >> The reason is that tools/bpf/resolve_btfids/Makefile passes header
> >> include paths by extending HOSTCFLAGS which is overridden by setting
> >> HOSTCFLAGS in the make command (because of Makefile rules [1]).
> >>
> >> This patch fixes the above problem by passing the include paths via
> >> `HOSTCFLAGS_resolve_btfids` which is used by tools/build/Build.include
> >> and can be combined with overridding HOSTCFLAGS.
> >>
> >> [1] https://www.gnu.org/software/make/manual/html_node/Overriding.html
> >>
> >> Fixes: 56a2df7615fa ("tools/resolve_btfids: Compile resolve_btfids as host program")
> >> Signed-off-by: Viktor Malik <vmalik@redhat.com>
> >> ---
> >>  tools/bpf/resolve_btfids/Makefile | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> >> index ac548a7baa73..4b8079f294f6 100644
> >> --- a/tools/bpf/resolve_btfids/Makefile
> >> +++ b/tools/bpf/resolve_btfids/Makefile
> >> @@ -67,7 +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 $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
> >>  
> >> -HOSTCFLAGS += -g \
> >> +HOSTCFLAGS_resolve_btfids += -g \
> >>            -I$(srctree)/tools/include \
> >>            -I$(srctree)/tools/include/uapi \
> >>            -I$(LIBBPF_INCLUDE) \
> >> @@ -76,7 +76,7 @@ HOSTCFLAGS += -g \
> >>  
> >>  LIBS = $(LIBELF_LIBS) -lz
> >>  
> >> -export srctree OUTPUT HOSTCFLAGS Q HOSTCC HOSTLD HOSTAR
> >> +export srctree OUTPUT HOSTCFLAGS_resolve_btfids Q HOSTCC HOSTLD HOSTAR
> > 
> > hum, AFAICS this way the spacified HOSTCFLAGS="-O2" won't be pushed
> > to the libbpf and libsubcmd dependencies, right?
> 
> IIUC, it will, b/c we're doing:
> 
>     HOST_OVERRIDES := ... EXTRA_CFLAGS="$(HOSTCFLAGS)"
> 
> and then pass HOST_OVERRIDES to libbpf and libsubcmd builds, which will
> then pick EXTRA_CFLAGS as a part of their build.
> 
> Confirmed for libsubcmd:
> 
>     $ make HOSTCFLAGS="-O2" V=1 | grep libsubcmd | grep O2 | wc -l
>     14
>     $ make V=1 | grep libsubcmd | grep O2 | wc -l
>     0
> 
> Interestingly, I couldn't do the same for libbpf. It looks like libbpf
> is not rebuilt for resolve_btfids b/c resolve_btfids/Makefile uses
> $(BPFOBJ) as the libbpf target and selftests/bpf/Makefile passes
> BPFOBJ=$(HOST_BPFOBJ) to the resolve_btfids build. So, an already built
> libbpf is reused and that one hasn't picked HOSTCFLAGS.
> 
> > how about we add the EXTRA_CFLAGS variable like we do in libbpf,
> > libsubcmd or perf
> > 
> > with the change below you'd need to run:
> > 
> >   $ make EXTRA_CFLAGS="-O2"
> > 
> 
> I'd like to avoid that b/c then, we would need to issue a different make
> command for the BPF selftests than for the rest of the kernel to pass
> custom flags to host-built programs.

ok

> 
> > I'll dig up the cross build scenarious we broke last time we
> > touched this stuff, perhaps Ian might remember as well ;-)
> 
> That will be useful, thanks :-)

there's test described by Nathan in here:

https://lore.kernel.org/bpf/Y9mFVNEi5wAINARY@dev-arch.thelio-3990X/

jirka

> 
> Viktor
> 
> > 
> > jirka
> > 
> > 
> > ---
> > diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> > index ac548a7baa73..58cfedc9c2db 100644
> > --- a/tools/bpf/resolve_btfids/Makefile
> > +++ b/tools/bpf/resolve_btfids/Makefile
> > @@ -18,8 +18,8 @@ else
> >  endif
> >  
> >  # Overrides for the prepare step libraries.
> > -HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > -		  CROSS_COMPILE="" EXTRA_CFLAGS="$(HOSTCFLAGS)"
> > +HOST_OVERRIDES = AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> > +		  CROSS_COMPILE=""
> >  
> >  RM      ?= rm
> >  HOSTCC  ?= gcc
> > @@ -67,7 +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)
> >  
> > -HOSTCFLAGS += -g \
> > +HOSTCFLAGS += $(EXTRA_CFLAGS) -g \
> >            -I$(srctree)/tools/include \
> >            -I$(srctree)/tools/include/uapi \
> >            -I$(LIBBPF_INCLUDE) \
> > @@ -76,7 +76,7 @@ HOSTCFLAGS += -g \
> >  
> >  LIBS = $(LIBELF_LIBS) -lz
> >  
> > -export srctree OUTPUT HOSTCFLAGS Q HOSTCC HOSTLD HOSTAR
> > +export srctree OUTPUT HOSTCFLAGS Q HOSTCC HOSTLD HOSTAR EXTRA_CFLAGS
> >  include $(srctree)/tools/build/Makefile.include
> >  
> >  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> > 
>