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Date: Tue, 27 Feb 2018 20:01:10 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: clz instruction is unavailable for Thumb1

On Tue, Feb 27, 2018 at 04:37:15PM -0800, Andre McCurdy wrote:
> On Tue, Feb 27, 2018 at 4:03 PM, Zhao, Weiming <weimingz@...eaurora.org> wrote:
> > In arch/arm/atomic_arch.h, it checks for __ARM_ARCH >= 5, which is not
> > sufficient.
> >
> > for example, for armv6-m, it only support Thumb1, which doesn't include clz.
> >
> > Suggest to check if it's building for thumb1:
> 
> Musl does not currently support Thumb 1.

I forget what the situation with v6-m is, and whether/how it could be
supportable. Is it really thumb1 or some thumb2 subset that fills
deficiencies? My recollection was that thumb1 lacks atomics, barriers,
thread-pointer loading, and maybe even syscalls, and since the
kuser_helper addresses are arm addresses, you can't even use them to
get the missing functionality.

Rich


> > diff --git a/arch/arm/atomic_arch.h b/arch/arm/atomic_arch.h
> > index c5c56f8..e3cb66a 100644
> > --- a/arch/arm/atomic_arch.h
> > +++ b/arch/arm/atomic_arch.h
> > @@ -82,7 +82,7 @@ static inline void a_crash()
> >                 : : : "memory");
> >  }
> >
> > -#if __ARM_ARCH >= 5
> > +#if __ARM_ARCH >= 5 && !(defined(__thumb__) && !defined(__thumb2))
> >
> >
> >
> > --
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by
> > The Linux Foundation
> >

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