User space atomic ops on ARMv5 and earlier [LWN.net]

User space atomic ops on ARMv5 and earlier

Posted Jan 13, 2009 19:39 UTC (Tue) by npitre (subscriber, #5680)
In reply to: User space atomic ops on ARMv5 and earlier by endecotp
Parent article: ARM SoC launched with Linux support (Linux Devices)

NPTL support for ARM in glibc certainly does. I developed the kernel part in collaboration with the person who did the glibc part.

As to gcc, I don't see any specific ARM support for the __sync_* primitives, not even for ARMv6+ which has native instructions that could be used for that purpose. However this should be easy to implement following the PA model. Incidentally, the file gcc/config/pa/linux-atomic.c contains this note:

/* Linux-specific atomic operations for PA Linux.
   Copyright (C) 2008 Free Software Foundation, Inc.
   Based on code contributed by CodeSourcery for ARM EABI Linux.
   Modifications for PA Linux by Helge Deller <deller@gmx.de>
[...]

So maybe that support does exist somewhere already?

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User space atomic ops on ARMv5 and earlier

Posted Jan 13, 2009 22:18 UTC (Tue) by endecotp (guest, #36428) [Link]

I've just done a quick test and it looks like gcc emits a function call when you invoke __sync_* for ARM. So presumably it would be possible to write a small library of things with the right names that calls the kernel helper code. Then near-optimal portable code would be possible.

Maybe someone has already done this....