Re: [PULL 0/2] Libslirp patches

[Paolo Bonzini]

On 05/07/21 18:31, Peter Maydell wrote:
> 8 here means "8 bytes", not "8 bits". And indeed on i386 you can't
> do 8-byte atomics with simple insns.

You can, there's a cmpxchg8b instruction.  The problem is that somehow 
configure's view of this disagrees with what happens during compilation.

If anybody can send a config.log and make V=1 log, I can look at it.

Paolo

> The compiler's answer to this
> is "emit a call to a helper in libatomic, which will emulate an
> atomic access by taking some kind of lock". We don't ever want to
> fall back to "take a lock" because sometimes our accesses to the
> atomic variables are from TCG generated code -- this is why we
> don't link against libatomic. The problem is that we have not
> correctly detected that this compiler can't do inline atomics
> for 64-bit values and avoided using them. But at least we have
> made this a compile failure rather than a silently-wrong-code bug:-)