66   assert(hdr != obj && hdr != disp_hdr && obj != disp_hdr, "registers must be different");
  67   Label done;
  68   int null_check_offset = -1;
  69 
  70   verify_oop(obj);
  71 
  72   // save object being locked into the BasicObjectLock
  73   str(obj, Address(disp_hdr, BasicObjectLock::obj_offset_in_bytes()));
  74 
  75   if (UseBiasedLocking) {
  76     assert(scratch != noreg, "should have scratch register at this point");
  77     null_check_offset = biased_locking_enter(disp_hdr, obj, hdr, scratch, false, done, &slow_case);
  78   } else {
  79     null_check_offset = offset();
  80   }
  81 
  82   // Load object header
  83   ldr(hdr, Address(obj, hdr_offset));
  84   // and mark it as unlocked
  85   orr(hdr, hdr, markOopDesc::unlocked_value);






  86   // save unlocked object header into the displaced header location on the stack
  87   str(hdr, Address(disp_hdr, 0));
  88   // test if object header is still the same (i.e. unlocked), and if so, store the
  89   // displaced header address in the object header - if it is not the same, get the
  90   // object header instead
  91   lea(rscratch2, Address(obj, hdr_offset));
  92   cmpxchgptr(hdr, disp_hdr, rscratch2, rscratch1, done, /*fallthough*/NULL);
  93   // if the object header was the same, we're done
  94   // if the object header was not the same, it is now in the hdr register
  95   // => test if it is a stack pointer into the same stack (recursive locking), i.e.:
  96   //
  97   // 1) (hdr & aligned_mask) == 0
  98   // 2) sp <= hdr
  99   // 3) hdr <= sp + page_size
 100   //
 101   // these 3 tests can be done by evaluating the following expression:
 102   //
 103   // (hdr - sp) & (aligned_mask - page_size)
 104   //
 105   // assuming both the stack pointer and page_size have their least

  66   assert(hdr != obj && hdr != disp_hdr && obj != disp_hdr, "registers must be different");
  67   Label done;
  68   int null_check_offset = -1;
  69 
  70   verify_oop(obj);
  71 
  72   // save object being locked into the BasicObjectLock
  73   str(obj, Address(disp_hdr, BasicObjectLock::obj_offset_in_bytes()));
  74 
  75   if (UseBiasedLocking) {
  76     assert(scratch != noreg, "should have scratch register at this point");
  77     null_check_offset = biased_locking_enter(disp_hdr, obj, hdr, scratch, false, done, &slow_case);
  78   } else {
  79     null_check_offset = offset();
  80   }
  81 
  82   // Load object header
  83   ldr(hdr, Address(obj, hdr_offset));
  84   // and mark it as unlocked
  85   orr(hdr, hdr, markOopDesc::unlocked_value);
  86 
  87   if (EnableValhalla && !UseBiasedLocking) {
  88     // Mask always_locked bit such that we go to the slow path if object is a value type
  89     andr(hdr, hdr, ~markOopDesc::biased_lock_bit_in_place);
  90   }
  91 
  92   // save unlocked object header into the displaced header location on the stack
  93   str(hdr, Address(disp_hdr, 0));
  94   // test if object header is still the same (i.e. unlocked), and if so, store the
  95   // displaced header address in the object header - if it is not the same, get the
  96   // object header instead
  97   lea(rscratch2, Address(obj, hdr_offset));
  98   cmpxchgptr(hdr, disp_hdr, rscratch2, rscratch1, done, /*fallthough*/NULL);
  99   // if the object header was the same, we're done
 100   // if the object header was not the same, it is now in the hdr register
 101   // => test if it is a stack pointer into the same stack (recursive locking), i.e.:
 102   //
 103   // 1) (hdr & aligned_mask) == 0
 104   // 2) sp <= hdr
 105   // 3) hdr <= sp + page_size
 106   //
 107   // these 3 tests can be done by evaluating the following expression:
 108   //
 109   // (hdr - sp) & (aligned_mask - page_size)
 110   //
 111   // assuming both the stack pointer and page_size have their least