linux-kernel - Re: Error: invalid switch -me200

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Date:   Mon, 16 Nov 2020 16:26:30 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Segher Boessenkool <segher@...nel.crashing.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        mihai.caraman@...escale.com,
        Nathan Chancellor <natechancellor@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Brian Cain <bcain@...eaurora.org>,
        Fāng-ruì Sòng 
        <maskray@...gle.com>, kernel test robot <lkp@...el.com>,
        kbuild-all@...ts.01.org,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: Error: invalid switch -me200


Quoting Michael Ellerman <mpe@...erman.id.au>:

> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>> Le 14/11/2020 à 01:20, Segher Boessenkool a écrit :
>>> On Fri, Nov 13, 2020 at 12:14:18PM -0800, Nick Desaulniers wrote:
>>>>>>> Error: invalid switch -me200
>>>>>>> Error: unrecognized option -me200
>>>>>>
>>>>>> 251 cpu-as-$(CONFIG_E200)   += -Wa,-me200
>>>>>>
>>>>>> Are those all broken configs, or is Kconfig messed up such that
>>>>>> randconfig can select these when it should not?
>>>>>
>>>>> Hmmm, looks like this flag does not exist in mainline binutils? There is
>>>>> a thread in 2010 about this that Segher commented on:
>>>>>
>>>>> https://lore.kernel.org/linuxppc-dev/9859E645-954D-4D07-8003-FFCD2391AB6E@kernel.crashing.org/
>>>>>
>>>>> Guess this config should be eliminated?
>>>
>>> The help text for this config options says that e200 is used in 55xx,
>>> and there *is* an -me5500 GAS flag (which probably does this same
>>> thing, too).  But is any of this tested, or useful, or wanted?
>>>
>>> Maybe Christophe knows, cc:ed.
>>>
>>
>> I don't have much clue on this.
>
> Me either.
>
>> But I see on wikipedia that e5500 is a 64 bits powerpc  
>> (https://en.wikipedia.org/wiki/PowerPC_e5500)
>>
>> What I see is that NXP seems to provide a GCC version that includes  
>> aditionnal cpu (e200z0 e200z2
>> e200z3 e200z4 e200z6 e200z7):
>>
>> valid arguments to '-mcpu=' are: 401 403 405 405fp 440 440fp 464  
>> 464fp 476 476fp 505 601 602 603
>> 603e 604 604e 620 630 740 7400 7450 750 801 821 823 8540 8548 860  
>> 970 G3 G4 G5 a2 cell e200z0 e200z2
>> e200z3 e200z4 e200z6 e200z7 e300c2 e300c3 e500mc e500mc64 e5500  
>> e6500 ec603e native power3 power4
>> power5 power5+ power6 power6x power7 power8 powerpc powerpc64  
>> powerpc64le rs64 titan "
>>
>> https://community.nxp.com/t5/MPC5xxx/GCC-generating-not-implemented-instructions/m-p/845049
>>
>> Apparently based on binutils 2.28
>>
>> https://www.nxp.com/docs/en/release-note/S32DS-POWER-v1-2-RN.pdf
>>
>> But that's not exactly -me200 though.
>>
>> Now, I can't see any defconfig that selects CONFIG_E200, so is that  
>> worth keeping it in the kernel
>> at all ?
>
> There was a commit in 2014 that suggests it worked at least to some
> extent then:
>
>   3477e71d5319 ("powerpc/booke: Restrict SPE exception handlers to  
> e200/e500 cores")

Not sure, that patch seems to be focussed on the new e500mc

>
>
> Presumably there was a non-upstream toolchain where it was supported?
>
> AFAICS the kernel builds OK with just the cpu-as modification removed:
>
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index a4d56f0a41d9..16b8336f91dd 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -248,7 +248,6 @@ KBUILD_CFLAGS               += $(call  
> cc-option,-mno-string)
>  cpu-as-$(CONFIG_40x)           += -Wa,-m405
>  cpu-as-$(CONFIG_44x)           += -Wa,-m440
>  cpu-as-$(CONFIG_ALTIVEC)       += $(call as-option,-Wa$(comma)-maltivec)
> -cpu-as-$(CONFIG_E200)          += -Wa,-me200
>  cpu-as-$(CONFIG_E500)          += -Wa,-me500
>
>  # When using '-many -mpower4' gas will first try and find a matching power4
>
>
> So that seems like the obvious fix for now.

Or we could do

diff --git a/arch/powerpc/platforms/Kconfig.cputype  
b/arch/powerpc/platforms/Kconfig.cputype
index c194c4ae8bc7..a11cf9431e1e 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -67,6 +67,7 @@ config 44x
  	select PHYS_64BIT

  config E200
+	depends on $(cc-option,-me200)
  	bool "Freescale e200"

  endchoice
---
Christophe