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

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.

-- 
-=( Ian Abbott <abbotti@mev.co.uk> || MEV Ltd. is a company  )=-
-=( registered in England & Wales.  Regd. number: 02862268.  )=-
-=( Regd. addr.: S11 & 12 Building 67, Europa Business Park, )=-
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Re: Build failures with CC=arm-linux-gnueabihf-gcc-11

[Michael Olbrich]

On Thu, Nov 18, 2021 at 03:32:04PM +0000, Ian Abbott wrote:
> 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):

It probably is added from here:

arch-$(CONFIG_CPU_32v7)		:=-D__LINUX_ARM_ARCH__=7 $(call cc-option,-march=armv7-a,-march=armv5t -Wa$(comma)-march=armv7-a)

The check for -march=armv7-a fails for some reason so the fallback is used.

I've seen this when CC is a wrapper and already adds -mcpu=... to the
commandline. In that case gcc now complains about the combination and the
check fails.

Michael

> 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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Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
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Re: Build failures with CC=arm-linux-gnueabihf-gcc-11

[Ian Abbott]

Hi Michael,

On 19/11/2021 09:29, Michael Olbrich wrote:
> On Thu, Nov 18, 2021 at 03:32:04PM +0000, Ian Abbott wrote:
>> 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):
> 
> It probably is added from here:
> 
> arch-$(CONFIG_CPU_32v7)		:=-D__LINUX_ARM_ARCH__=7 $(call cc-option,-march=armv7-a,-march=armv5t -Wa$(comma)-march=armv7-a)
> 
> The check for -march=armv7-a fails for some reason so the fallback is used.

Yes, I showed the exact failure resulting from the cc-option call 
further down my email:

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

> I've seen this when CC is a wrapper and already adds -mcpu=... to the
> commandline. In that case gcc now complains about the combination and the
> check fails.

In my case, CC was set by this "build.sh" script:

#! /bin/sh
 

SRC="../barebox-de0-nano-soc" 

ARCH="arm"
CROSS_COMPILE=arm-linux-gnueabihf-
CC='$(CROSS_COMPILE)gcc-11'

make -C "$SRC" O=`pwd` ARCH="$ARCH" CROSS_COMPILE="$CROSS_COMPILE" 
CC="$CC" $*


so after expansion, CC=arm-linux-gnueabihf-gcc-11

> 
> Michael

Cheers, Ian.

> 
>> 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.
> 


-- 
-=( Ian Abbott <abbotti@mev.co.uk> || MEV Ltd. is a company  )=-
-=( registered in England & Wales.  Regd. number: 02862268.  )=-
-=( Regd. addr.: S11 & 12 Building 67, Europa Business Park, )=-
-=( Bird Hall Lane, STOCKPORT, SK3 0XA, UK. || www.mev.co.uk )=-

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