RFR: 8199138: Add RISC-V support to Zero

[Edward Nevill]

On Sun, 2018-03-18 at 14:37 +0000, Andrew Haley wrote:
> On 03/17/2018 07:02 PM, Edward Nevill wrote:
> > Webrev: http://cr.openjdk.java.net/~enevill/8199138/webrev.00
> > 
> > This webrev add Zero support for RISC-V
> 
> What happens with atomics?  Do we fall back to GCC builtins for everything?
> 

Pretty much. The only atomic operation which doesn't used GCC builtins is os::atomic_copy64. For RISC-V this just does the same as all other 64 bit CPUs.

    *(jlong *) dst = *(const jlong *) src;

Interestingly, there is no implementation of atomic_copy64 for ARM32. I guess it just relies on the compiler generating LDRD/STRD correctly and  doesn't support earlier ARM32 archs. I'll do a bit of investigation.

For reference here is the implementation of atomic_copy64.

Regards,
Ed.

--- CUT ---
  static void atomic_copy64(const volatile void *src, volatile void *dst) {
#if defined(PPC32) && !defined(__SPE__)
    double tmp;
    asm volatile ("lfd  %0, %2\n"
                  "stfd %0, %1\n"
                  : "=&f"(tmp), "=Q"(*(volatile double*)dst)
                  : "Q"(*(volatile double*)src));
#elif defined(PPC32) && defined(__SPE__)
    long tmp;
    asm volatile ("evldd  %0, %2\n"
                  "evstdd %0, %1\n"
                  : "=&r"(tmp), "=Q"(*(volatile long*)dst)
                  : "Q"(*(volatile long*)src));
#elif defined(S390) && !defined(_LP64)
    double tmp;
    asm volatile ("ld  %0, 0(%1)\n"
                  "std %0, 0(%2)\n"
                  : "=r"(tmp)
                  : "a"(src), "a"(dst));
#else
    *(jlong *) dst = *(const jlong *) src;
#endif
--- CUT ---