linux-kernel - Re: [PATCH] powerpc: e500: Fix compilation with gcc e500 compiler

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Date:   Sat, 9 Jul 2022 09:26:11 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Arnd Bergmann <arnd@...db.de>,
        Pali Rohár <pali@...nel.org>
CC:     Michael Ellerman <michael@...erman.id.au>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc: e500: Fix compilation with gcc e500 compiler



Le 08/07/2022 à 22:04, Arnd Bergmann a écrit :
> On Fri, Jul 8, 2022 at 7:12 PM Pali Rohár <pali@...nel.org> wrote:
>>
>> On Monday 04 July 2022 14:07:10 Arnd Bergmann wrote:
>>> Another problem I see is that a kernel that is built for both E500 and E500MC
>>> uses -mcpu=e500mc and may not actually work on the older ones either
>>> (even with your patch).
>>
>> Such configuration is not supported, see arch/powerpc/platforms/Kconfig.cputype:
>>
>> config PPC_E500MC
>>          bool "e500mc Support"
>>          select PPC_FPU
>>          select COMMON_CLK
>>          depends on E500
>>          help
>>            This must be enabled for running on e500mc (and derivatives
>>            such as e5500/e6500), and must be disabled for running on
>>            e500v1 or e500v2.
>>
>> Based on this option you can enable either support for e500v1/e500v2 or
>> for e500mc. But not both.
> 
> This looks like a bad decision in Kconfig though, as there is nothing
> enforcing the rule: If you want support for E500MC, you have to select
> PPC_85xx, which implies E500 and allows selecting any combination
> of E500v1, E500v2 and E500MC based machines, but enabling
> any E500MC based one breaks all the others.
> 
> If this is a hard dependency, I think it should be enforced by making
> E500MC a separate top-level option in the "Processor Type" choice
> statement. However, if they can actually coexist, the help text and
> the Makefile need to be fixed.
> 

While looking at this discussion, I discovered that with GCC 12 from 
https://mirrors.edge.kernel.org/pub/tools/crosstool/ I'm unable to build 
a corenet64_smp_defconfig:

If I select the GENERIC_CPU or e5500 (with altivec) I get:

   CC      arch/powerpc/kernel/irq.o
{standard input}: Assembler messages:
{standard input}:3535: Error: unrecognized opcode: `wrteei'
{standard input}:5608: Error: unrecognized opcode: `wrteei'

   CC      arch/powerpc/kernel/pmc.o
{standard input}: Assembler messages:
{standard input}:42: Error: unrecognized opcode: `mfpmr'
{standard input}:53: Error: unrecognized opcode: `mtpmr'


If I select the e5500 (without altivec) or e6500 I get:

   CC      arch/powerpc/kernel/io.o
{standard input}: Assembler messages:
{standard input}:381: Error: unrecognized opcode: `eieio'
{standard input}:444: Error: unrecognized opcode: `eieio'
{standard input}:480: Error: unrecognized opcode: `eieio'
{standard input}:506: Error: unrecognized opcode: `eieio'
{standard input}:552: Error: unrecognized opcode: `eieio'
{standard input}:817: Error: unrecognized opcode: `eieio'
{standard input}:839: Error: unrecognized opcode: `eieio'
{standard input}:885: Error: unrecognized opcode: `eieio'
{standard input}:1106: Error: unrecognized opcode: `eieio'
{standard input}:1130: Error: unrecognized opcode: `eieio'
{standard input}:1174: Error: unrecognized opcode: `eieio'
{standard input}:1393: Error: unrecognized opcode: `eieio'
{standard input}:1417: Error: unrecognized opcode: `eieio'
{standard input}:1461: Error: unrecognized opcode: `eieio'



Christophe