linux-kernel - Re: [RFC PATCH v1] power: don't manage floating point regs when no FPU

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Message-ID: <da699207-b172-cf12-a04f-4444313e3e27@csgroup.eu>
Date:   Tue, 11 Aug 2020 16:06:44 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v1] power: don't manage floating point regs when no
 FPU



Le 11/08/2020 à 14:07, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>   10 files changed, 44 insertions(+), 1 deletion(-)
> 
> In general this looks fine.
> 
> It's a bit #ifdef heavy. Maybe some of those can be cleaned up a bit
> with some wrapper inlines?

Looking at it once more, looks like more or less the same level of 
#ifdefs as things like CONFIG_ALTIVEC for instance. I can't really see 
much opportunities to clean it up.

> 
>> diff --git a/arch/powerpc/kernel/ptrace/ptrace-novsx.c b/arch/powerpc/kernel/ptrace/ptrace-novsx.c
>> index b2dc4e92d11a..8f87a11f3f8c 100644
>> --- a/arch/powerpc/kernel/ptrace/ptrace-novsx.c
>> +++ b/arch/powerpc/kernel/ptrace/ptrace-novsx.c
>> @@ -28,6 +29,9 @@ int fpr_get(struct task_struct *target, const struct user_regset *regset,
>>   
>>   	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
>>   				   &target->thread.fp_state, 0, -1);
>> +#else
>> +	return 0;
>> +#endif
> 
> Should we return -ENODEV/EIO here? Wonder if another arch can give us a clue.
> 

Looks like we have to do another way  ... another #ifdef ... in the 
definition of native_regsets[] in ptrace-view.c . And then we should be 
able to not build ptrace-novsx.c at all. Will try that.

Christophe