Build failures with CC=arm-linux-gnueabihf-gcc-11

[Ian Abbott]

Hi,

My Debian "testing" build system updated the default version of 
arm-linux-gnueabihf-gcc from 10.x to 11.x.  Building barebox in thumb-2 
mode for an ARMv7 (it's a SoCFPGA) with this compiler fails with 
assembler errors such as:

   CC      common/state/state_variables.o
{standard input}: Assembler messages:
{standard input}:1535: Error: selected processor does not support `rev 
r3,r3' in Thumb mode
{standard input}:1576: Error: selected processor does not support `rev 
r3,r3' in Thumb mode

Building in verbose mode (V=1) shows that "make" has selected the 
compile flags `-march=armv5t -Wa,-march=armv7-a` instead of the usual 
`-march=armv7-a`.

Looking a little deeper, all of the following lines in 
"arch/arm/Makefile" are failing to select the first option and 
defaulting to the second option (if any):

arch-$(CONFIG_CPU_64v8)		:= -D__LINUX_ARM_ARCH__=8 $(call 
cc-option,-march=armv8-a)
arch-$(CONFIG_CPU_32v7)		:=-D__LINUX_ARM_ARCH__=7 $(call 
cc-option,-march=armv7-a,-march=armv5t -Wa$(comma)-march=armv7-a)
arch-$(CONFIG_CPU_32v6)		:=-D__LINUX_ARM_ARCH__=6 $(call 
cc-option,-march=armv6,-march=armv5t -Wa$(comma)-march=armv6)
arch-$(CONFIG_CPU_32v5)		:=-D__LINUX_ARM_ARCH__=5 $(call 
cc-option,-march=armv5te,-march=armv4t)

The error from the compiler is:

cc1: error: ‘-mfloat-abi=hard’: selected architecture lacks an FPU

(Note: the error is only shown after tweaking the `try-run` command in 
"scripts/Kbuild.include" so that it does not send error output to 
"/dev/null".)

That error seems to be a change in behaviour between GCC 10.x and GCC 11.x.

At the point in the Makefile that the error occurs, the `-msoft-float` 
option has not been added to `KBUILD_CPPFLAGS` yet. That is done further 
down the Makefile except for `CONFIG_CPU_V8`.  I guess it needs to be 
added somewhere before problematic lines in the Makefile.  I'm not sure 
if `-msoft-float` is also needed for 64-bit ARMv8, but the error 
suggests it is required there too.

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