linux-kernel - Re: [PATCH] arm64: write_sysreg asm illegal for aarch32

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Message-ID: <ba7f7072-88e5-92ee-f573-4282b6a082d4@android.com>
Date:   Wed, 1 Nov 2017 11:16:43 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Robin Murphy <robin.murphy@....com>, linux-kernel@...r.kernel.org,
        Christoffer Dall <cdall@...aro.org>,
        Stefan Traby <stefan@...lo-penguin.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Dave Martin <Dave.Martin@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: write_sysreg asm illegal for aarch32

On 11/01/2017 10:56 AM, Mark Rutland wrote:
> On Wed, Nov 01, 2017 at 10:49:00AM -0700, Mark Salyzyn wrote:
>> On 11/01/2017 10:14 AM, Robin Murphy wrote:
>>> On 01/11/17 16:58, Mark Salyzyn wrote:
>>>> Cross compiling to aarch32 (for vdso32) using clang correctly
>>>> identifies that (the unused) write_sysreg inline asm directive is
>>>> illegal in that architectural context:
>>>>
>>>> arch/arm64/include/asm/arch_timer.h: error: invalid input constraint 'rZ' in asm
>>>>           write_sysreg(cntkctl, cntkctl_el1);
>>>>           ^
>>>> arch/arm64/include/asm/sysreg.h: note: expanded from macro 'write_sysreg'
>>>>                        : : "rZ" (__val));
>>>>                            ^
>>>>
>>>> GCC normally checks for correctness everywhere. But uniquely for
>>>> unused asm, will optimize out and suppress the error report.
>>> It sounds more like some paths are wrong in the compat vDSO build if
>>> it's pulling in this header in the first place - nothing in this file is
>>> relevant to AArch32.
>>>
>>> Robin.
>>>
>> And yet, when you CROSS_COMPILE_ARM32 a vdso32, you have no choice but to
>> utilize the arm64 headers since they contain all the relevant kernel
>> structures and environment.
> This itself is the underlying issue.
>
> When building the compat VDSO, we must ensure that we only include
> headers that make sense for 32-bit arm.
>
> If the build system can't do that today, we should rework it so that it
> can. Anything else cannot be a complete fix.
>
>> asm/arch_timer.h (remember we are using arm instructions to access arch64
>> timers)
>>
>> linux/time.h (really only for struct timespec())
>>
>> asm/processor.h (eg: cpu_relax())
>>
>> pull in a _lot_ of architectural related cruft that always somehow picks up
>> asm/sysreg.h somewhere in the multitude of includes to fulfill some unused
>> inline's needs.
> ... these are just the particular symptoms this problem results in
> today.
>
> Thanks,
> Mark.

Ok, will attack it and see just how bad the scale is...

These ones trouble me ... there was no intent to pick up the wrong pieces.

In file included from ./include/linux/time.h:4:
In file included from ./include/linux/cache.h:5:
In file included from ./arch/arm64/include/asm/cache.h:19:
In file included from ./arch/arm64/include/asm/cachetype.h:19:
In file included from ./arch/arm64/include/asm/cputype.h:94:
./arch/arm64/include/asm/sysreg.h:303:2: error: invalid input constraint 
'rZ' in asm

In file included from ./include/linux/hrtimer.h:18:
In file included from ./include/linux/rbtree.h:34:
In file included from ./include/linux/rcupdate.h:47:
In file included from ./include/linux/ktime.h:25:
In file included from ./include/linux/jiffies.h:8:
In file included from ./include/linux/timex.h:65:
In file included from ./arch/arm64/include/asm/timex.h:19:
./arch/arm64/include/asm/arch_timer.h:83:4: error: invalid input 
constraint 'rZ' in asm

         write_sysreg(cntkctl, cntkctl_el1);
         ^

./arch/arm64/include/asm/sysreg.h:278:12: note: expanded from macro 
'write_sysreg'
                      : : "rZ" (__val));

-- Mark