linux-kernel - Re: [Bug report] __arch

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Message-ID: <7738ff3a-3f5a-2583-93f7-458425fd84a5@genode-labs.com>
Date:   Tue, 27 Jun 2023 18:57:32 +0200
From:   Sebastian Sumpf <Sebastian.Sumpf@...ode-labs.com>
To:     Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Richard Weinberger <richard@....at>
Cc:     tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [Bug report] __arch_hweight32/64 x86

On 6/27/23 06:25, Borislav Petkov wrote:
> On Mon, Jun 26, 2023 at 03:41:27PM -0700, Dave Hansen wrote:
>> I'm not even sure that UML needs GENERIC_HWEIGHT.  From a quick glance,
>> it looks like x86 used to use GENERIC_HWEIGHT, but got arch-specific
>> versions later.  UML just never moved over to the arch-specific versions.
> 
> Thanks - that could very well be the explanation.
> 
> That bug report made me blink a couple of times since I did take extra
> precaution to not clobber regs in arch/x86/lib/hweight.S as this was
> part of the whole pain back then with calling a function from asm where
> gcc doesn't even know we're calling a function, see:
> 
> f5967101e9de ("x86/hweight: Get rid of the special calling convention")
> 
>> I _think_ the attached patch might just fix the problems with the C
>> version and bring the x86/UML implementation back in line with the rest
>> of x86.
>>
>> Thoughts?
> 
>> diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
>> index 186f13268401..76d507860be4 100644
>> --- a/arch/x86/um/Kconfig
>> +++ b/arch/x86/um/Kconfig
>> @@ -44,6 +44,3 @@ config ARCH_HAS_SC_SIGNALS
>>   
>>   config ARCH_REUSE_HOST_VSYSCALL_AREA
>>   	def_bool !64BIT
>> -
>> -config GENERIC_HWEIGHT
>> -	def_bool y
> 
> Yeah, we should do it. UML should not do anything different wrt calling
> conventions so it should be able to handle the arch/x86/lib/hweight.S
> versions just fine.

Thank you for the quick resolution! It fixes the problem for me and sorry for 
not explaining well enough.

> Richi?
> 

-- 
Sebastian Sumpf
Genode Labs

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