linux-kernel - Re: [PATCH/RFC] Re: linux-next: build failure after merge of the luto-misc tree

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Date:	Thu, 21 Jul 2016 22:41:18 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC] Re: linux-next: build failure after merge of the
 luto-misc tree

On Fri, Jul 22, 2016 at 09:23:02AM +1000, Stephen Rothwell wrote:
> Hi Arnaldo,
> 
> On Thu, 21 Jul 2016 10:12:48 -0300 Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> >
> > Em Thu, Jul 21, 2016 at 09:29:50AM +1000, Stephen Rothwell escreveu:
> > > Hi Arnaldo,
> > > 
> > > On Tue, 19 Jul 2016 23:52:02 -0300 Arnaldo Carvalho de Melo <acme@...nel.org> wrote:  
> > > >
> > > > Humm, it seems that the compiler used is not the cross one, but the
> > > > native, check if, say, __powerpc__ is defined.  
> > > 
> > > Yes, __powerpc__ is defined (unsuprisingly).  
> > 
> > Maybe this one?
> > 
> > diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
> > index 1f75b0a046cc..3500fcf7bd47 100644
> > --- a/tools/objtool/Makefile
> > +++ b/tools/objtool/Makefile
> > @@ -1,10 +1,14 @@
> >  include ../scripts/Makefile.include
> >  
> > +HOSTARCH=$(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
> > +                                -e s/sun4u/sparc64/ \
> > +                                -e s/arm.*/arm/ -e s/sa110/arm/ \
> > +                                -e s/s390x/s390/ -e s/parisc64/parisc/ \
> > +                                -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
> > +                                -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ )
> > +
> >  ifndef ($(ARCH))
> > -ARCH ?= $(shell uname -m)
> > -ifeq ($(ARCH),x86_64)
> > -ARCH := x86
> > -endif
> > +ARCH ?= $(HOSTARCH)
> >  endif
> >  
> >  # always use the host compiler
> > @@ -26,7 +30,7 @@ OBJTOOL_IN := $(OBJTOOL)-in.o
> >  
> >  all: $(OBJTOOL)
> >  
> > -INCLUDES := -I$(srctree)/tools/include -I$(srctree)/tools/arch/$(ARCH)/include/uapi
> > +INCLUDES := -I$(srctree)/tools/include -I$(srctree)/tools/arch/$(HOSTARCH)/include/uapi
> >  CFLAGS   += -Wall -Werror $(EXTRA_WARNINGS) -fomit-frame-pointer -O2 -g $(INCLUDES)
> >  LDFLAGS  += -lelf $(LIBSUBCMD)
> >  
> 
> That gets me this errors from the x86_64 allmodconfig build:
> 
> tools/objtool/objtool-in.o: In function `decode_instructions':
> tools/objtool/builtin-check.c:276: undefined reference to `arch_decode_instruction'
> 
> It just looks like objtool was not written with cross compilation in
> mind?

I don't know yet what the specific problem is, but objtool should work
fine in a cross-compiled environment.  It needs to be compiled with the
host (powerpc) compiler, but then it needs to disassemble target (x86)
files.  It worked fine before the bitsperlong.h files were merged.

I can try to take a deeper look at it tomorrow.

> It seems to build and run OK when you remove the test that
> checks that BITS_PER_LONG and __BITS_PER_LONG are the same, but I have
> no idea if it getting the desired results.

-- 
Josh