Re: [Qemu-devel] [PATCH v2 00/27] cmpxchg-based emulation of atomics

[Richard Henderson]

On 07/01/2016 10:04 AM, Richard Henderson wrote:
> I spent a couple evenings this week tweaking Emilio's patch set.
> 
> The first major change is to "qemu/int128.h", so that we can use
> that type in the context of a 16-byte cmpxchg.  I have yet to teach
> TCG code generation about this type, so it's really only usable
> from other helper functions.  But that's still an improvement over
> having to return two uint64_t by reference.
> 
> The second major change is to funnel atomic operation generation
> through functions in tcg-op.c.  There we can test whether or not
> we're generating code in a parallel context and require atomic
> operations.  This also centralizes the helper functions so that we
> don't have to have the same sets in every target.
> 
> The third major change is providing a mechanism by which we can
> trap on atomic operations that we do not support, exit the cpu loop,
> stop the world, and then re-execute the instruction in a serial context.
> This is obviously something that will need to be filled in further
> as MTTCG progresses.
> 
> This minimally tested, but it is good enough to boot Fedora 24 x86-64,
> even with the softmmu single-step stubbed out.  Perhaps unsurprisingly,
> Fedora does not attempt an unaligned atomic operation.

I should have mentioned -- this was based on my tcg-next branch, for which I
just sent a pull request (in particular, Sergey's alignment improvement patch).

I pushed my patchset to

  git://github.com/rth7680/qemu.git atomic-2

for ease of browsing.


r~