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From: Rich Felker <dalias@libc.org>
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Subject: Re: Custom __set_thread_area for ARM
Date: Tue, 13 Jan 2015 22:09:46 -0500
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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.

Rich