Re: membar_enter semantics

[Martin Husemann <martin%duskware.de@localhost>]

On Fri, Feb 11, 2022 at 11:33:39AM -0500, Mouse wrote:
> >> sparc64: [...]
> > Almost forgot to mention ... I wouldn't read too much into how sparc64's bar$
> 
> Is that choice run-time configurable?  I thought it was baked into the
> hardware...but admittedly that's based on documents I read Quite Some
> Time Ago.

For v9 it can be set per process even. See the TSTATE_MM_* bits:

#define PSTATE_MM       0x0c0   /* memory model */
#define PSTATE_MM_TSO   0x000   /* total store order */
#define PSTATE_MM_PSO   0x040   /* partial store order */
#define PSTATE_MM_RMO   0x080   /* Relaxed memory order */

And we use TSO for the kernel:

#define PSTATE_KERN     (PSTATE_MM_TSO|PSTATE_PRIV)

so Jason is correct. For userland we default to RMO for 64bit binaries
(but honor their elf flags), and TSO for 32bit.

Martin