src/cpu/aarch64/vm/macroAssembler_aarch64.cpp

rev 12409 : 8169177: aarch64: SIGSEGV when "-XX:+ZeroTLAB" is specified along with GC options
Summary: Add zero-initialization to C1 for fast TLAB refills
Reviewed-by: aph, drwhite
Contributed-by: kavitha.natarajan@linaro.org

*** 3942,3957 ****
--- 3942,4027 ----
    str(top, Address(rthread, in_bytes(JavaThread::tlab_start_offset())));
    str(top, Address(rthread, in_bytes(JavaThread::tlab_top_offset())));
    add(top, top, t1);
    sub(top, top, (int32_t)ThreadLocalAllocBuffer::alignment_reserve_in_bytes());
    str(top, Address(rthread, in_bytes(JavaThread::tlab_end_offset())));
+ 
+   if (ZeroTLAB) {
+     // This is a fast TLAB refill, therefore the GC is not notified of it.
+     // So compiled code must fill the new TLAB with zeroes.
+     ldr(top, Address(rthread, in_bytes(JavaThread::tlab_start_offset())));
+     zero_memory(top,t1,t2);
+   }
+ 
    verify_tlab();
    b(retry);
  
    return rthread; // for use by caller
  }
  
+ // Zero words; len is in bytes
+ // Destroys all registers except addr
+ // len must be a nonzero multiple of wordSize
+ void MacroAssembler::zero_memory(Register addr, Register len, Register t1) {
+   assert_different_registers(addr, len, t1, rscratch1, rscratch2);
+ 
+ #ifdef ASSERT
+   { Label L;
+     tst(len, BytesPerWord - 1);
+     br(Assembler::EQ, L);
+     stop("len is not a multiple of BytesPerWord");
+     bind(L);
+   }
+ #endif
+ 
+ #ifndef PRODUCT
+   block_comment("zero memory");
+ #endif
+ 
+   Label loop;
+   Label entry;
+ 
+ //  Algorithm:
+ //
+ //    scratch1 = cnt & 7;
+ //    cnt -= scratch1;
+ //    p += scratch1;
+ //    switch (scratch1) {
+ //      do {
+ //        cnt -= 8;
+ //          p[-8] = 0;
+ //        case 7:
+ //          p[-7] = 0;
+ //        case 6:
+ //          p[-6] = 0;
+ //          // ...
+ //        case 1:
+ //          p[-1] = 0;
+ //        case 0:
+ //          p += 8;
+ //      } while (cnt);
+ //    }
+ 
+   const int unroll = 8; // Number of str(zr) instructions we'll unroll
+ 
+   lsr(len, len, LogBytesPerWord);
+   andr(rscratch1, len, unroll - 1);  // tmp1 = cnt % unroll
+   sub(len, len, rscratch1);      // cnt -= unroll
+   // t1 always points to the end of the region we're about to zero
+   add(t1, addr, rscratch1, Assembler::LSL, LogBytesPerWord);
+   adr(rscratch2, entry);
+   sub(rscratch2, rscratch2, rscratch1, Assembler::LSL, 2);
+   br(rscratch2);
+   bind(loop);
+   sub(len, len, unroll);
+   for (int i = -unroll; i < 0; i++)
+     str(zr, Address(t1, i * wordSize));
+   bind(entry);
+   add(t1, t1, unroll * wordSize);
+   cbnz(len, loop);
+ }
+ 
  // Defines obj, preserves var_size_in_bytes
  void MacroAssembler::eden_allocate(Register obj,
                                     Register var_size_in_bytes,
                                     int con_size_in_bytes,
                                     Register t1,