/* * We default to false if we know other options have been enabled *
which are currently incompatible with MTTCG. Otherwise when each *
guest (target) has been updated to support: * - atomic instructions
* - memory ordering primitives (barriers) * they can set the
appropriate CONFIG flags in ${target}-softmmu.mak * * Once a guest
architecture has been converted to the new primitives * there are two
remaining limitations to check. * * - The guest can't be oversized
(e.g. 64 bit guest on 32 bit host) * - The host must have a stronger
memory order than the guest * * It may be possible in future to
support strong guests on weak hosts * but that will require tagging
all load/stores in a guest with their * implicit memory order
requirements which would likely slow things * down a lot. */
static bool check_tcg_memory_orders_compatible(void)
{
#if defined(TCG_GUEST_DEFAULT_MO) && defined(TCG_TARGET_DEFAULT_MO)
return (TCG_GUEST_DEFAULT_MO & ~TCG_TARGET_DEFAULT_MO) == 0;
#else
return false;
#endif
}
That function will return false for x86_64 on ARM64.
On tcg/aarch64/tcg-target.h
#define TCG_TARGET_DEFAULT_MO (0)
On target/i386/cpu.h
/* The x86 has a strong memory model with some store-after-load re-ordering */
#define TCG_GUEST_DEFAULT_MO (TCG_MO_ALL & ~TCG_MO_ST_LD)
I am asking for clarification because the above code will default x86 on
ARM64 to disable MTTCG.
