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 arm-specific hints - specifically a description
44 * of padding required to keep all 64-bit parameters properly aligned.
45 *
46 * ARM JNI hint format
47 *
48 *       LLLL FFFFFFFF FFFFFFFF FFFFFFFF
49 *
50 *   L - number of double-words of storage required on the stack (0-30 words)
51 *   F - pad flag -- if set, write a pad word to the stack before copying
52 *       the next 32 bits
53 *
54 * If there are too many arguments to construct valid hints, this function will
55 * return a result with the S bit set.
56 */
57u4 dvmPlatformInvokeHints(const DexProto* proto)
58{
59    const char* sig = dexProtoGetShorty(proto);
60    int padFlags, jniHints;
61    char sigByte;
62    int stackOffset, padMask, hints;
63
64    stackOffset = padFlags = 0;
65    padMask = 0x00000001;
66
67    /* Skip past the return type */
68    sig++;
69
70    while (true) {
71        sigByte = *(sig++);
72
73        if (sigByte == '\0')
74            break;
75
76        if (sigByte == 'D' || sigByte == 'J') {
77            if ((stackOffset & 1) != 0) {
78                padFlags |= padMask;
79                stackOffset++;
80                padMask <<= 1;
81            }
82            stackOffset += 2;
83            padMask <<= 2;
84        } else {
85            stackOffset++;
86            padMask <<= 1;
87        }
88    }
89
90    jniHints = 0;
91
92    if (stackOffset > DALVIK_JNI_COUNT_SHIFT) {
93        /* too big for "fast" version */
94        jniHints = DALVIK_JNI_NO_ARG_INFO;
95    } else {
96        assert((padFlags & (0xffffffff << DALVIK_JNI_COUNT_SHIFT)) == 0);
97        stackOffset -= 2;           // r2/r3 holds first two items
98        if (stackOffset < 0)
99            stackOffset = 0;
100        jniHints |= ((stackOffset+1) / 2) << DALVIK_JNI_COUNT_SHIFT;
101        jniHints |= padFlags;
102    }
103
104    return jniHints;
105}
106