Re: [PATCH 2/3] powerpc: use default endianness for converting guest/init

From: Michael Ellerman <mpe@ellerman.id.au>
To: Andre Przywara <andre.przywara@arm.com>
Cc: Will Deacon <Will.Deacon@arm.com>, Matt Evans <matt@ozlabs.org>,
	"kvm-ppc@vger.kernel.org" <kvm-ppc@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Subject: Re: [PATCH 2/3] powerpc: use default endianness for converting guest/init
Date: Fri, 19 Jun 2015 11:08:41 +1000	[thread overview]
Message-ID: <1434676121.23771.1.camel@ellerman.id.au> (raw)
In-Reply-To: <5582DB16.8060808@arm.com>

On Thu, 2015-06-18 at 15:52 +0100, Andre Przywara wrote:
> Hi,
> 
> On 06/17/2015 10:43 AM, Andre Przywara wrote:
> > For converting the guest/init binary into an object file, we call
> > the linker binary, setting the endianness to big endian explicitly
> > when compiling kvmtool for powerpc.
> > This breaks if the compiler is actually targetting little endian
> > (which is true for the Debian port, for instance).
> > Remove the explicit big endianness switch from the linker call to
> > allow linking on little endian PowerPC builds again.
> > 
> > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > ---
> > Hi,
> > 
> > this fixed the powerpc64le build for me, while still compiling fine
> > for big endian. Admittedly this whole init->guest_init.o conversion
> > has its issues (with MIPS, for instance), which deserve proper fixing,
> > but lets just fix that build for now.
> 
> Will was concerned about breaking toolchains where the linker does not
> default to 64-bit. Is that an issue we care about?

Yeah, that would be Debian & Ubuntu BE at least, and maybe Fedora too? I'm not
sure how you compiled it big endian?

> AFAICT LDFLAGS is only used in this dodgy binary-to-object-file
> conversion of guest/init. For this we rely on the resulting .o file to
> have the same ELF target as the other object files to be finally linked
> into the lkvm binary. As we don't compile guest/init with CFLAGS, there
> is a possible mismatch.
> 
> I am looking into a proper fix for this now (compiling guest/init with
> CFLAGS, calling $CC with linker options instead of $LD and allowing CC
> and LD override). Still struggling with MIPS, though :-(

Yeah that's obviously a better solution medium term.

Can you do something like this? Sorry untested:

diff --git a/Makefile b/Makefile
index 6110b8e..8663d67 100644
--- a/Makefile
+++ b/Makefile
@@ -149,7 +149,11 @@ ifeq ($(ARCH), powerpc)
        OBJS    += powerpc/xics.o
        ARCH_INCLUDE := powerpc/include
        CFLAGS  += -m64
-       LDFLAGS += -m elf64ppc
+       ifeq ($(call try-build,$(SOURCE_HELLO),$(CFLAGS),-m elf64ppc),y)
+               LDFLAGS += -m elf64ppc
+       else
+               LDFLAGS += -m elf64leppc
+       endif
 
        ARCH_WANT_LIBFDT := y
 endif


cheers


