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      1 /*
      2  * Copyright (C) 2008 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 /*
     17  * Target-specific optimization and run-time hints
     18  */
     19 
     20 
     21 #include "Dalvik.h"
     22 #include "libdex/DexClass.h"
     23 
     24 #include <stdlib.h>
     25 #include <stddef.h>
     26 #include <sys/stat.h>
     27 
     28 
     29 /*
     30  * The class loader will associate with each method a 32-bit info word
     31  * (jniArgInfo) to support JNI calls.  The high order 4 bits of this word
     32  * are the same for all targets, while the lower 28 are used for hints to
     33  * allow accelerated JNI bridge transfers.
     34  *
     35  * jniArgInfo (32-bit int) layout:
     36  *
     37  *    SRRRHHHH HHHHHHHH HHHHHHHH HHHHHHHH
     38  *
     39  *    S - if set, ignore the hints and do things the hard way (scan signature)
     40  *    R - return-type enumeration
     41  *    H - target-specific hints (see below for details)
     42  *
     43  * This function produces x86-specific hints for the standard 32-bit 386 ABI.
     44  * Note that the JNI requirements are very close to the 386 runtime model.  In
     45  * particular, natural datatype alignments do not apply to passed arguments.
     46  * All arguments have 32-bit alignment.  As a result, we don't have to worry
     47  * about padding - just total size.  The only tricky bit is that floating point
     48  * return values come back on the FP stack.
     49  *
     50  *
     51  * 386 ABI JNI hint format
     52  *
     53  *       ZZZZ ZZZZZZZZ AAAAAAAA AAAAAAAA
     54  *
     55  *   Z - reserved, must be 0
     56  *   A - size of variable argument block in 32-bit words (note - does not
     57  *       include JNIEnv or clazz)
     58  *
     59  * For the 386 ABI, valid hints should always be generated.
     60  */
     61 u4 dvmPlatformInvokeHints( const DexProto* proto)
     62 {
     63     const char* sig = dexProtoGetShorty(proto);
     64     unsigned int jniHints, wordCount;
     65     char sigByte;
     66 
     67     wordCount = 0;
     68     while (true) {
     69         sigByte = *(sig++);
     70 
     71         if (sigByte == '\0')
     72             break;
     73 
     74         wordCount++;
     75 
     76         if (sigByte == 'D' || sigByte == 'J') {
     77             wordCount++;
     78         }
     79     }
     80 
     81     if (wordCount > 0xFFFF) {
     82         /* Invalid - Dex file limitation */
     83         jniHints = DALVIK_JNI_NO_ARG_INFO;
     84     } else {
     85         jniHints = wordCount;
     86     }
     87 
     88     return jniHints;
     89 }
     90