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

@@ -3942,16 +3942,86 @@
   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,