[PATCH] Bug fix in TemplateTable::iop2 (JDK9 aarch32)

[Xiang Yuan]

Hi, All:
  Our team fix a bug in JDK9 aarch32 template interpreter, the detail is
described below:

*Test Case:*
/***************code start***************/
public class Iop2 {
         public static void main(String args[]) {
                   int shift_bits = 36; //0x24, 0b00100100
                   int data = 0x87654321;

                   System.out.println(Integer.toHexString(data <<
shift_bits));
                   System.out.println(Integer.toHexString(data >>
shift_bits));
                   System.out.println(Integer.toHexString(data >>>
shift_bits));
         }
}
/***************code end****************/

The result of Openjdk9(aarch32):
0
ffffffff
0

The correct result:
76543210
f8765432
8765432

*Bug Description:*
    This test case uses Java bytecodes ishl, ishr and iushr. To interpret
them, aarch32 instructions lsl, asr and lsr are used directly in the
procedure “void TemplateTable::iop2(Operation op) in
./hotspot/src/cpu/aarch32/vm/templateTable_aarch32.cpp”.

/***************code start***************/
       case shl  : __ lsl(r0, r1, r0);  break;
       case shr  : __ asr(r0, r1, r0);  break;
       case ushr : __ lsr(r0, r1, r0);  break;
/***************code end****************/

    The r1 is the int value need to be shifted, and the r0 is the shift
bits.

    The JVM Specification requires that for these 3 bytecodes, they pop two
int values from the expression stack as value2 and value1, and then they
shift value1 by the low 5 bits of value2. However, these aarch32
instructions shift
value1 by the low 8 bits of value2. And the semantics of aarch32
instructions don’t match the Java bytecodes. And therefore, using aarch32
instruction to interpret these Java bytecodes directly will get a wrong
result.

*Bug Solution:*
         Clear the high 27 bits of value2 before shifting can fix this bug.
/***************code start***************/
       case shl  : __ andr(r0, r0, 31); __ lsl(r0, r1, r0);  break;
       case shr  : __ andr(r0, r0, 31); __ asr(r0, r1, r0);  break;
       case ushr : __ andr(r0, r0, 31); __ lsr(r0, r1, r0);  break;
/***************code end****************/

*Bug Patch:*
/***************patch start***************/
--- a/src/cpu/aarch32/vm/templateTable_aarch32.cpp Wed Dec 23 12:21:32 2015
+0000
+++ b/src/cpu/aarch32/vm/templateTable_aarch32.cpp       Mon Dec 28
17:12:30 2015 +0800
@@ -1275,9 +1275,9 @@
   case _and : __ andr(r0, r1, r0); break;
   case _or  : __ orr(r0, r1, r0);  break;
   case _xor : __ eor(r0, r1, r0);  break;
-  case shl  : __ lsl(r0, r1, r0);  break;
-  case shr  : __ asr(r0, r1, r0);  break;
-  case ushr : __ lsr(r0, r1, r0);  break;
+  case shl  : __ andr(r0, r0, 31); __ lsl(r0, r1, r0);  break;
+  case shr  : __ andr(r0, r0, 31); __ asr(r0, r1, r0);  break;
+ case ushr : __ andr(r0, r0, 31); __ lsr(r0, r1, r0);  break;
   default   : ShouldNotReachHere();
   }
}
/***************patch end****************/

  And the attachment are the test case and patch.

  Best regards!
-------------- next part --------------
--- a/src/cpu/aarch32/vm/templateTable_aarch32.cpp	Wed Dec 23 12:21:32 2015 +0000
+++ b/src/cpu/aarch32/vm/templateTable_aarch32.cpp	Tue Dec 29 18:50:42 2015 +0800
@@ -1275,9 +1275,9 @@
   case _and : __ andr(r0, r1, r0); break;
   case _or  : __ orr(r0, r1, r0);  break;
   case _xor : __ eor(r0, r1, r0);  break;
-  case shl  : __ lsl(r0, r1, r0);  break;
-  case shr  : __ asr(r0, r1, r0);  break;
-  case ushr : __ lsr(r0, r1, r0);  break;
+  case shl  : __ andr(r0, r0, 31); __ lsl(r0, r1, r0);  break;
+  case shr  : __ andr(r0, r0, 31); __ asr(r0, r1, r0);  break;
+  case ushr : __ andr(r0, r0, 31); __ lsr(r0, r1, r0);  break;
   default   : ShouldNotReachHere();
   }
 }