[Skiboot] [PATCH] external: Fix cross compilation issue

[Patrick Williams]

On Thu, Jul 28, 2016 at 10:23:05PM +1000, oliver wrote:
> On Thu, Jul 28, 2016 at 8:40 PM, Patrick Williams <patrick at stwcx.xyz> wrote:
> > On Thu, Jul 28, 2016 at 03:05:38PM +0530, Vasant Hegde wrote:
> >> For some reason Makefile thinks compiler variables like CC is already
> >> assigned and ignores CROSS_COMPILE flags. Hence I'm not able to generate
> >> arm binary on x86.
> >>
> >> Use default assignment operator instead of conditional assignment
> >> operator (?=) in Makefile.
> >>
> >> Fixes: 3137d249 (pflash: Allow building under yocto.)
> >> CC: Patrick Williams <patrick at stwcx.xyz>
> >> CC: Stewart Smith <stewart at linux.vnet.ibm.com>
> >> Signed-off-by: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>
> >> ---
> >>  external/common/rules.mk | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/external/common/rules.mk b/external/common/rules.mk
> >> index bb12fd5..416a40d 100644
> >> --- a/external/common/rules.mk
> >> +++ b/external/common/rules.mk
> >> @@ -1,5 +1,5 @@
> >> -CC ?= $(CROSS_COMPILE)gcc
> >> -LD ?= $(CROSS_COMPILE)ld
> >> +CC = $(CROSS_COMPILE)gcc
> >> +LD = $(CROSS_COMPILE)ld
> >
> > This effectively undoes the change I made in 3137d249, so I'm not sure
> > why we would want it or why it is needed.
> 
> make automatically defines CC so the ?= assignment is never done. You
> can get the desired
> behaviour with and ifdef block though:
> 
> diff --git a/external/common/rules.mk b/external/common/rules.mk
> index 5558cd3..4dd7942 100644
> --- a/external/common/rules.mk
> +++ b/external/common/rules.mk
> @@ -1,5 +1,8 @@
> -CC ?= $(CROSS_COMPILE)gcc
> -LD ?= $(CROSS_COMPILE)ld
> +ifdef CROSS_COMPILE
> +CC = $(CROSS_COMPILE)gcc
> +LD = $(CROSS_COMPILE)ld
> +endif
> +

I don't think that is sufficient for Yocto either.  The current
environment variables for a qemux86-64 target are:

CROSS_COMPILE=x86_64-openbmc-linux-
CC=x86_64-openbmc-linux-gcc -m64 -march=core2 -mtune=core2 -msse3
       -mfpmath=sse
       --sysroot=...sdk/sysroots/core2-64-openbmc-linux
LD=x86_64-openbmc-linux-ld
        --sysroot=...sdk/sysroots/core2-64-openbmc-linux

An ARM target would have something similar.

As you see both CROSS_COMPILE and CC/LD are set, but CC/LD are not
as simple as $(CROSS_COMPILE)gcc.  Also, by forcing gcc whenever
CROSS_COMPILE is set, you end up precluding the use of clang, which is
supported by Yocto.

>  ARCH := $(shell $(GET_ARCH) "$(CROSS_COMPILE)")
> 
>  ifeq ($(ARCH),ARCH_ARM)
> 
> 
> > Yocto sets CC and LD directly and actually adds some of the CFLAGS onto
> > the CC variable (for right or wrong).  Thus it doesn't use CROSS_COMPILE
> > directly.  Also, by forcing 'CC = $(CROSS_COMPILE)gcc' we preclude the
> > use of clang.
> 
> Forcing the assignment is a bad idea, but keep in mind that most of us
> aren't using
> Yocto. I hit this problem while trying to build a copy of pflash for
> an unopened BMC
> and needed to use their toolchain. Manually setting CC/LD from the command line
> works, but the external/ tools should respect CROSS_COMPILE for consistency with
> skiboot itself and linux.
> 
> >
> >>  ARCH := $(shell $(GET_ARCH) "$(CROSS_COMPILE)")
> >>
> >>  ifeq ($(ARCH),ARCH_ARM)
> >> --
> >> 2.5.5
> >>
> >
> > --
> > Patrick Williams
> >
> > _______________________________________________
> > Skiboot mailing list
> > Skiboot at lists.ozlabs.org
> > https://lists.ozlabs.org/listinfo/skiboot
> >

-- 
Patrick Williams
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