free()上的SIGSEGV

Question

我正在移植一个C程序。

我遇到的问题是free()上的SIGSEGV。我不明白它的根本原因是什么。看起来堆内存被什么东西损坏了。这种情况有时不会发生，但很常见。

malloc未返回NULL。所以内存分配可能是正确的。

我正在NexusOne 2.2.1上测试它，我使用的是Android NDK、r5b和Android SDK，以及Eclipse ADT和Cygwin。我正在使用android.content.res.AssetFileDescriptor读取C模块中的资源。

以下是问题出现时ndk-gdb中的消息。

(gdb) c
Continuing.

Breakpoint 2, Java_kr_co_pkbio_Unse_DangSaJuShinSal (env=0xaa50,
    obj=0x4495b970)
    at C:/DEWR/Product/Software-Engineering/Eclipse-Workspace/Unse/jni/unse.c:1
83
1083                    free(strBuf);
(gdb) next

Program received signal SIGSEGV, Segmentation fault.
0xafd11c80 in __libc_android_abort ()
   from C:/DEWR/Product/Software-Engineering/Eclipse-Workspace/Unse/obj/local/a
meabi/libc.so
(gdb) bt
#0  0xafd11c80 in __libc_android_abort ()
   from C:/DEWR/Product/Software-Engineering/Eclipse-Workspace/Unse/obj/local/a
meabi/libc.so
#1  0xbec233bc in ?? ()
Cannot access memory at address 0xc
(gdb) quit

这是Java源代码...

public static HashMap<String, FileInfoForNativeCode> fifnMap = new HashMap<String, FileInfoForNativeCode>();
public static FileInfoForNativeCode openAssets(String fname) {
    FileInfoForNativeCode fifn;

    if (Constants.VERBOSE_LOGS)
        Log.d("TAGG", "TAGG openAssets("+fname+")");

    fifn = fifnMap.get(fname);
    if (fifn != null)
        return fifn;

    AssetFileDescriptor myDescriptor = null;
    try {
        myDescriptor = assetManager.openFd(fname+".jet");
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
    FileDescriptor fd = myDescriptor.getFileDescriptor();
    long off = myDescriptor.getStartOffset();
    long len = myDescriptor.getLength();

    if (Constants.VERBOSE_LOGS)
        Log.d("TAGG", "TAGG fd:"+fd+" off:"+off+" len:"+len);

    fifn = new FileInfoForNativeCode(off, len, fd, myDescriptor);
    fifnMap.put(fname, fifn);
    return fifn;
}

这是C源代码..。

char* getTextByIndex (TextFileBufType *filebuf, char *index) {
    #define _INDEX_PREFIX_    '@'
    int        i, j, lenBuf;
    char    *result;
    char    indexPrefix = _INDEX_PREFIX_;
    int        lenIndexPrefix = utf8len( &indexPrefix );
    int        lenIndex = strlen(index);

    for ( i = 0 ; i < filebuf->total ; i++ ) {
        //__android_log_print(ANDROID_LOG_DEBUG,"TAG", "JNI : %d -> %s", i, filebuf->text[i]);

        if ( memcmp (filebuf->text[i], &indexPrefix, lenIndexPrefix) != 0 )
            continue;

        if ( memcmp (filebuf->text[i]+lenIndexPrefix, index, lenIndex) != 0 )
            continue;

        lenBuf = 0;
        lenBuf += strlen(filebuf->text[i]);
        lenBuf++;
        for ( j = i+1 ; j < filebuf->total ; j++ ) {
            if ( memcmp (filebuf->text[j], &indexPrefix, lenIndexPrefix) == 0 )
                break;

            lenBuf += strlen(filebuf->text[j]);
            lenBuf++;
        }

        result = malloc(lenBuf);
        result[0] = 0;
        strcat(result, filebuf->text[i]);
        strcat(result, "\n");
        for ( j = i+1 ; j < filebuf->total ; j++ ) {
            if ( memcmp (filebuf->text[j], &indexPrefix, lenIndexPrefix) == 0 )
                break;

            strcat(result, filebuf->text[j]);
            strcat(result, "\n");
        }

        //__android_log_print(ANDROID_LOG_DEBUG,"TAG", "JNI : %d!!! -> %s", i, filebuf->text[i]);
        return result;
    }

    return NULL;

    #undef _INDEX_PREFIX_
}

inline void readyFileInFile (FileInFile *fif, char *path)
{
    jstring jstrFpath;
    jobject finfo;
    jobject descriptor;

    jstrFpath = (*gEnv)->NewStringUTF(gEnv, path);
    finfo = (*gEnv)->CallStaticObjectMethod(gEnv, clsUtility, midOpenAssets, jstrFpath);
    fif->offset = (*gEnv)->GetLongField(gEnv, finfo, fidOffset);
    fif->length = (*gEnv)->GetLongField(gEnv, finfo, fidLength);
    descriptor = (*gEnv)->GetObjectField(gEnv, finfo, fidDescriptor);
    fif->fd = (*gEnv)->GetIntField(gEnv, descriptor, fidDescriptorFileDescriptor);
}

jobjectArray Java_kr_co_pkbio_Unse_DangSaJuShinSal (JNIEnv *env, jobject obj) {
//    char   *fname = "DangSaJu_ShinSal";
    int     i, fileno[4], ret_code, type;
    char    temp[256];
    char   *header[4] = { "년", "월", "일", "시" };
    char    table1[12] = { 1, 0, 3, 2, 1, 0, 3, 2, 1, 0, 3, 2 };
    char    table2[4]  = {10, 7, 4, 1};

    char   *index[12] = {
        "겁살",   "재살",   "천살",   "지살",   "연살",   "월살",
        "망신살", "장성살", "반안살", "역마살", "육해살", "화개살"
    };

    int        r_option;
    int        numBytesRead;
    char    *strBuf;
    TextFileBufType    filebuf;
    jstring buf_output[4];
    jobjectArray output;
    FileInFile fif;

    gEnv = env;

    /* 년월일시에 대한 겁살을 계산한다 */
    type = table1[BaseInfo.saju.day % 12];
    fileno[0] = (table2[type] + (BaseInfo.saju.year  % 12)) % 12;
    fileno[1] = (table2[type] + (BaseInfo.saju.month % 12)) % 12;
    fileno[2] = (table2[type] + (BaseInfo.saju.day   % 12)) % 12;
    fileno[3] = (table2[type] + (BaseInfo.saju.hour  % 12)) % 12;
    /*WriteMsg (" - 기본위치 : 생일지지(%s) --> type:%d --> 자(%s)에 대한 살:%s\n",
        JeeJeeStr[BaseInfo.saju.day % 12], type, JeeJeeStr[0], index[table2[type]]);
    WriteMsg (" - 년살     : 생년지지(%s) --> 년%s\n", JeeJeeStr[BaseInfo.saju.year % 12],
        index[fileno[0]]);
    WriteMsg (" - 월살     : 생월지지(%s) --> 월%s\n", JeeJeeStr[BaseInfo.saju.month % 12],
        index[fileno[1]]);
    WriteMsg (" - 일살     : 생일지지(%s) --> 일%s\n", JeeJeeStr[BaseInfo.saju.day % 12],
        index[fileno[2]]);
    WriteMsg (" - 시살     : 생시지지(%s) --> 시%s\n", JeeJeeStr[BaseInfo.saju.hour % 12],
        index[fileno[3]]);*/


    readyFileInFile(&fif, "data/DangSaJu5.dat");

    r_option = ((int)'#' << 8) & 0xFF00;   /* Comment char setting */
    r_option |= (RT_OPT_RMCMT | RT_OPT_RMCRLF | RT_OPT_LTRIM | RT_OPT_RTRIM | RT_OPT_SPACES);

    if ( ReadTextFileToBufA (&filebuf, &fif, r_option) < 0 ) {
        __android_log_print(ANDROID_LOG_ERROR,"TAG", "JNI : 서버측에서 치명적인 오류가 발생하여 더이상 진행할 수 없습니다.");
        return NULL;
    }

    for ( i = 0 ; i < 4 ; i++ ) {
        sprintf (temp, "%s%s", header[i], index[fileno[i]]);
        strBuf = getTextByIndex(&filebuf, temp);
        //__android_log_print(ANDROID_LOG_DEBUG,"TAG", "JNI : %s -> %s", temp, strBuf );
        buf_output[i] = (*gEnv)->NewStringUTF(gEnv, strBuf);
        free(strBuf); //line number : 1083 ***It doesn't cause SIGSEGV on first for-loop-round, but on third for-round.***
        //PrintTextFile3 ("../data/DangSaJu5.dat", temp, VIEW_T_R_STR,
        //    "12신살로 알아보는 인생의 길흉화복 : %s", temp);
        /*if (i < 3) {
            sprintf (temp, "\n 계속해서 %s%s에 대한 풀이를 보시겠습니까? (Y/n)",
                header[i+1], index[fileno[i+1]]);
            ret_code = GetYesNo (temp, GETYN_YES);
            if (ret_code == GETYN_NO)  return;
        }*/
    }

    FreeTextFileBuf (&filebuf);
    //printf ("\n [Enter]키를 누르세요.");  fflush(stdout);
    //PauseUntil (300, 0);
    #if defined (_DO_NOT_COMPILE_)
    {
        int j;
        for (i=0 ; i<4 ; i++) {
            for (j=0 ; j<12 ; j++) {
                sprintf (temp, "%s%s", header[i], index[j]);
                //PrintTextFile3 ("../data/DangSaJu5.dat", temp, VIEW_T_R_STR,
                //    "당사주 / 인생 길흉화복 datafile test : %s", temp);
            }
        }
    }
    #endif

    output = (*gEnv)->NewObjectArray(gEnv, 4, clsString, NULL);
    (*gEnv)->SetObjectArrayElement(gEnv, output, 0, buf_output[0]);
    (*gEnv)->SetObjectArrayElement(gEnv, output, 1, buf_output[1]);
    (*gEnv)->SetObjectArrayElement(gEnv, output, 2, buf_output[2]);
    (*gEnv)->SetObjectArrayElement(gEnv, output, 3, buf_output[3]);

    return output;
}

我在控制AssetFileDescriptors的生命周期。我不使用终止的FileDescriptors。我是否必须在Java中对I/O例程进行重新编码，或者不需要释放分配的内存？它经常导致第三个for循环上的SIGSEGV。但有时在第四个循环中。

    for ( i = 0 ; i < 4 ; i++ ) {
        sprintf (temp, "%s%s", header[i], index[fileno[i]]);
        strBuf = getTextByIndex(&filebuf, temp); //malloc() in this function.
        if (strBuf == NULL)
            buf_output[i] = NULL;
        else

        {
            buf_output[i] = (*gEnv)->NewStringUTF(gEnv, strBuf);
            free(strBuf);
        }
    }

Answer 1

我已经通过将这一行代码放在空闲(StrBuf)之后进行了调试；(虽然没有重复的空闲(StrBuf)...)

strBuf = NULL;

Answer 2

我已经在Galaxy S上测试过了，它在Galaxy S (2.2)上运行良好。我没有在另一台Nexus One上尝试过，以便知道我的Nexus One是否有故障。

而且看起来AssetFileDescriptor不是问题的根源，因为当我没有直接访问资产文件而是访问复制的资产文件时，问题仍然存在。