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Date: Wed, 21 Jan 2015 17:45:56 -0800
From: Andy Lutomirski <luto@...capital.net>
To: musl@...ts.openwall.com
Subject: Re: Custom __set_thread_area for ARM

On 01/13/2015 07:09 PM, Rich Felker wrote:
> On Tue, Jan 13, 2015 at 11:19:44PM +0300, Oleg Ranevskyy wrote:
>> Dear community,
>>
>> Musl has a generic implementation of the __set_thread_area function in
>> src/thread/__set_thread_area.c. It is not used for ARM though. There is a
>> custom ARM implementation in src/thread/arm/__set_thread_area.s.
>>
>> Would you be able to clarify the following question please?
>> Why musl doesn't define SYS_set_thread_area for ARM to utilize the generic
>> function and uses custom __set_thread_area instead?
> 
> The ARM kernel does not implement SYS_set_thread_area. Instead it
> provides an ARM-specific syscall. The asm file you're looking at uses
> that instead.
> 
> BTW, this code is replaced in git master and the pending 1.1.6
> release. It's part of the ARM atomics/TLS access overhaul.

As the sort-of-maintainer of the kernel side of this on x86, I have to
ask: why is the i386 __set_thread_area function written in assembly?

--Andy

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