[Buildroot] SH4A target: error: command line option ‘-m4-nofpu’ is not supported by this configuration
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Fri Dec 2 08:58:21 UTC 2016
Hello,
First of all, thanks for your detailed bug report. It's very nice to
have such a minimal Buildroot .config and kernel configuration to
easily reproduce the problem.
On Thu, 1 Dec 2016 23:59:04 +0000, John Gulbrandsen wrote:
> I’m attempting to use buildroot to create cross-compiler, Linux kernel, boot loader etc. for a custom board that uses a Hitachi SH7786 CPU that has two SH4A CPU cores. It appears something goes wrong in the Linux build when a SH4A target CPU is selected in menuconfig. When a SH4 CPU is selected, everything builds fine but I would rather configure the build for my exact CPU. How do I fix this?
>
> Note that I have tried to use these additional GCC settings but no difference:
> BR2_EXTRA_GCC_CONFIG_OPTIONS="--with-multilib-list=m4a,m4a-nofpu"
> BR2_EXTRA_GCC_CONFIG_OPTIONS="--with-multilib-list=m4,m4-nofpu"
>
> See below for make (verbose) output. The below build uses this extra GCC options: BR2_EXTRA_GCC_CONFIG_OPTIONS="--with-multilib-list=m4a,m4a-nofpu"
We are already passing those options to the gcc build. From
package/gcc/gcc-final/gcc-final.mk:
# The kernel wants to use the -m4-nofpu option to make sure that it
# doesn't use floating point operations.
ifeq ($(BR2_sh4)$(BR2_sh4eb),y)
HOST_GCC_FINAL_CONF_OPTS += "--with-multilib-list=m4,m4-nofpu"
HOST_GCC_FINAL_GCC_LIB_DIR = $(HOST_DIR)/usr/$(GNU_TARGET_NAME)/lib/!m4*
endif
ifeq ($(BR2_sh4a)$(BR2_sh4aeb),y)
HOST_GCC_FINAL_CONF_OPTS += "--with-multilib-list=m4a,m4a-nofpu"
HOST_GCC_FINAL_GCC_LIB_DIR = $(HOST_DIR)/usr/$(GNU_TARGET_NAME)/lib/!m4*
endif
So I believe your problem is a mismatch between your CPU selection at
the Buildroot level and at the kernel level. You have configured your
Buildroot for SH4A (so the compiler supports m4a/m4a-nofpu), but the CPU
selected in the kernel configuration is a SH4, so the kernel uses the
-m4-nofpu option.
Here is what the kernel is doing:
cflags-$(CONFIG_CPU_SH4) := $(call cc-option,-m4,) \
$(call cc-option,-mno-implicit-fp,-m4-nofpu)
cflags-$(CONFIG_CPU_SH4A) += $(call cc-option,-m4a,) \
$(call cc-option,-m4a-nofpu,)
So, you need to either:
- Adjust your Buildroot configuration to use SH4
- Adjust your Linux kernel configuration to use a SH4A
I will run some test builds to verify my theory.
Best regards,
Thomas Petazzoni
--
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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