svn commit: r288121 - projects/clang370-import/contrib/libc++/src/support

[Warner Losh]

> On Sep 22, 2015, at 11:34 AM, Dimitry Andric <dim at freebsd.org> wrote:
>  NOTE: this needs to be fixed properly later on, by supplying library
>  functions implementing atomic operations for arm < v6.  We should
>  probably take those from sys/arm/arm/stdatomic.c, and stuff them into
>  either libgcc or compiler-rt.

I don’t think you can do that.

arm < v6 is special. The CPUs don’t have atomic operations. In the kernel,
we disable interrupts and do the op. You can’t do that in user land. Instead,
you have to use RAS (Restartable Atomic Sequences) and have the kernel
grok the RAS. Thankfully, the RAS support in the kernel is just the R in that.
But it does mean that we’ll have some work to do this properly.

I’m not entirely sure that your ‘fix’ makes things actually safe, even if it
seems to make them work today. I’ll have to study it more closely.

Warner

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