[v4,1/4] powerpc/kbuild: set default generic machine type for 32-bit compile

Message ID 20180516141458.18996-2-npiggin@gmail.com
State Superseded
Headers show
Series
  • powerpc patches for new Kconfig language
Related show

Commit Message

Nicholas Piggin May 16, 2018, 2:14 p.m.
Some 64-bit toolchains uses the wrong ISA variant for compiling 32-bit
kernels, even with -m32. Debian's powerpc64le is one such case, and
that is because it is built with --with-cpu=power8.

So when cross compiling a 32-bit kernel with a 64-bit toolchain, set
-mcpu=powerpc initially, which is the generic 32-bit powerpc machine
type and scheduling model. CPU and platform code can override this
with subsequent -mcpu flags if necessary.

This is not done for 32-bit toolchains otherwise it would override
their defaults, which are presumably set appropriately for the
environment (moreso than a 64-bit cross compiler).

This fixes a lot of build failures due to incompatible assembly when
compiling 32-bit kernel with th Debian powerpc64le 64-bit toolchain.

Cc: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/Makefile | 11 +++++++++++
 1 file changed, 11 insertions(+)

Comments

Masahiro Yamada May 29, 2018, 1:39 p.m. | #1
2018-05-16 23:14 GMT+09:00 Nicholas Piggin <npiggin@gmail.com>:
> Some 64-bit toolchains uses the wrong ISA variant for compiling 32-bit
> kernels, even with -m32. Debian's powerpc64le is one such case, and
> that is because it is built with --with-cpu=power8.
>
> So when cross compiling a 32-bit kernel with a 64-bit toolchain, set
> -mcpu=powerpc initially, which is the generic 32-bit powerpc machine
> type and scheduling model. CPU and platform code can override this
> with subsequent -mcpu flags if necessary.
>
> This is not done for 32-bit toolchains otherwise it would override
> their defaults, which are presumably set appropriately for the
> environment (moreso than a 64-bit cross compiler).
>
> This fixes a lot of build failures due to incompatible assembly when
> compiling 32-bit kernel with th Debian powerpc64le 64-bit toolchain.
>
> Cc: Segher Boessenkool <segher@kernel.crashing.org>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---


Can you please remove the noise changes?

1/4 adds some blank lines, then 2/4 removes them.




>  arch/powerpc/Makefile | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index 95813df90801..15ca4bafad82 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -24,9 +24,20 @@ ifeq ($(HAS_BIARCH),y)
>  ifeq ($(CROSS32_COMPILE),)
>  CROSS32CC      := $(CC) -m32
>  KBUILD_ARFLAGS += --target=elf32-powerpc
> +

This blank line will be removed by the next patch.


> +ifdef CONFIG_PPC32
> +# These options will be overridden by any -mcpu option that the CPU
> +# or platform code sets later on the command line, but they are needed
> +# to set a sane 32-bit cpu target for the 64-bit cross compiler which
> +# may default to the wrong ISA.
> +KBUILD_CFLAGS          += -mcpu=powerpc
> +KBUILD_AFLAGS          += -mcpu=powerpc
> +endif
> +

This blank line will be removed by the next patch.


>  endif
>  endif
>
> +

This blank line will be removed by the next patch.



>  export CROSS32CC CROSS32AR
>
>  ifeq ($(CROSS_COMPILE),)
> --
> 2.17.0
>
> --
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Nicholas Piggin May 30, 2018, 10:43 a.m. | #2
On Tue, 29 May 2018 22:39:48 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> 2018-05-16 23:14 GMT+09:00 Nicholas Piggin <npiggin@gmail.com>:
> > Some 64-bit toolchains uses the wrong ISA variant for compiling 32-bit
> > kernels, even with -m32. Debian's powerpc64le is one such case, and
> > that is because it is built with --with-cpu=power8.
> >
> > So when cross compiling a 32-bit kernel with a 64-bit toolchain, set
> > -mcpu=powerpc initially, which is the generic 32-bit powerpc machine
> > type and scheduling model. CPU and platform code can override this
> > with subsequent -mcpu flags if necessary.
> >
> > This is not done for 32-bit toolchains otherwise it would override
> > their defaults, which are presumably set appropriately for the
> > environment (moreso than a 64-bit cross compiler).
> >
> > This fixes a lot of build failures due to incompatible assembly when
> > compiling 32-bit kernel with th Debian powerpc64le 64-bit toolchain.
> >
> > Cc: Segher Boessenkool <segher@kernel.crashing.org>
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > ---  
> 
> 
> Can you please remove the noise changes?
> 
> 1/4 adds some blank lines, then 2/4 removes them.

Okay sure, I will change that.

Thanks,
Nick

Patch

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 95813df90801..15ca4bafad82 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -24,9 +24,20 @@  ifeq ($(HAS_BIARCH),y)
 ifeq ($(CROSS32_COMPILE),)
 CROSS32CC	:= $(CC) -m32
 KBUILD_ARFLAGS	+= --target=elf32-powerpc
+
+ifdef CONFIG_PPC32
+# These options will be overridden by any -mcpu option that the CPU
+# or platform code sets later on the command line, but they are needed
+# to set a sane 32-bit cpu target for the 64-bit cross compiler which
+# may default to the wrong ISA.
+KBUILD_CFLAGS		+= -mcpu=powerpc
+KBUILD_AFLAGS		+= -mcpu=powerpc
+endif
+
 endif
 endif
 
+
 export CROSS32CC CROSS32AR
 
 ifeq ($(CROSS_COMPILE),)