| Message ID | 1440962970-17906-1-git-send-email-T.E.Baldwin99@members.leeds.ac.uk |
|---|---|
| State | New |
| Headers | show |
On 30 August 2015 at 20:29, Timothy E Baldwin <T.E.Baldwin99@members.leeds.ac.uk> wrote: > Implemented ARM __kernel_memory_barrier using GCC/clang > builtin __sync_synchronize(). > > Signed-off-by: Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk> > --- > linux-user/main.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/linux-user/main.c b/linux-user/main.c > index 2c9658e..f4b81b1 100644 > --- a/linux-user/main.c > +++ b/linux-user/main.c > @@ -531,7 +531,7 @@ do_kernel_trap(CPUARMState *env) > > switch (env->regs[15]) { > case 0xffff0fa0: /* __kernel_memory_barrier */ > - /* ??? No-op. Will need to do better for SMP. */ > + __sync_synchronize(); > break; I don't think this is correct, because this kernel usermode page entrypoint is just "do a DMB, however that works on this CPU's ARM architecture flavour". We implement DMB in target-arm/ as a no-op, and so no-op here is also the right thing. This does mean that we potentially have problems with multithreaded guests, but those don't currently work anyway. Fixing this requires a wider effort to implement memory barriers properly when we have multiple threads running QEMU guest CPUs at once, which may come out of the current MTTCG efforts. thanks -- PMM
diff --git a/linux-user/main.c b/linux-user/main.c index 2c9658e..f4b81b1 100644 --- a/linux-user/main.c +++ b/linux-user/main.c @@ -531,7 +531,7 @@ do_kernel_trap(CPUARMState *env) switch (env->regs[15]) { case 0xffff0fa0: /* __kernel_memory_barrier */ - /* ??? No-op. Will need to do better for SMP. */ + __sync_synchronize(); break; case 0xffff0fc0: /* __kernel_cmpxchg */ /* XXX: This only works between threads, not between processes.
Implemented ARM __kernel_memory_barrier using GCC/clang builtin __sync_synchronize(). Signed-off-by: Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk> --- linux-user/main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)