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Date: Tue, 27 Feb 2018 19:56:54 -0800
From: Khem Raj <>
To:, Rich Felker <>
Subject: Re: clz instruction is unavailable for Thumb1

On 2/27/18 5:01 PM, Rich Felker wrote:
> On Tue, Feb 27, 2018 at 04:37:15PM -0800, Andre McCurdy wrote:
>> On Tue, Feb 27, 2018 at 4:03 PM, Zhao, Weiming <> 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.

v6-m doesn't have MMU IIRC, but it might be interesting as a FDPIC

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