双指针分配中的分段错误

Question

I have declared double pointer like this

UInt8  **contentKeyCtx;

This variable is sent as argument to a function Inside the function there is local variable

 UInt8    *localckc     = NULL;
 localckc = calloc(1, localckcSize);

Then there is some array of values assigned to localckc

When i try to do this

 *contentKeyCtx = localckc;

I got Segmentation Fault

What i am doing wrong? Main function

int main (int argc, char *argv[])
{
    OSStatus result; // SInt32


    UInt8  *inBuff, *outBuff;
    UInt32 inBuffSize, outBuffSize;
    UInt8  **contentKeyCtx = calloc(1, sizeof(UInt8**));
    UInt32  *contentKeyCtxSize;
    FILE   *fp;


    const UInt8 *assetId = {0x1b, 0xf7, 0xf5, 0x3f, 0x5d, 0x5d, 0x5a, 0x1f};// what is this?



    inBuff=calloc(1,INBUFFSIZE);
    outBuff=calloc(1,OUTBUFFSIZE);


    inBuffSize = fread(inBuff, sizeof(UInt8), INBUFFSIZE, fp);

    fclose(fp);


    // IK we have some data. Now what?
    result = SKDServerGenCKC(inBuff, inBuffSize, assetId, contentKeyCtx, contentKeyCtxSize);


    free(inBuff);
    free(outBuff);
    printf("Result is  %d\n", result );
    return 0;
}

Actual function implementation

    OSStatus SKDServerGenCKC(
        const UInt8   *serverPlaybackCtx,
        UInt32         serverPlaybackCtxSize,
        const UInt8   *assetId,
        UInt8        **contentKeyCtx,
        UInt32        *contentKeyCtxSize)
{

    UInt8    *localckc     = NULL;
    UInt32    localckcSize = 0;
    PS_RequireAction(ckcContainer      != NULL, return kDRMSKDServerParamErr;)
    PS_RequireAction(contentKeyCtx     != NULL, return kDRMSKDServerParamErr;)
    PS_RequireAction(contentKeyCtxSize != NULL, return kDRMSKDServerParamErr;) 
    ...
     localckc = calloc(1, localckcSize);
     status = SKDServerWriteBytes(
                &ckcContainer->parser.currentOffset, PS_AES128_IV_SZ, 
                ckcContainer->aesKeyIV, localckcSize, localckc);


    ...
    *contentKeyCtx = localckc;


}

Answer 1

The function implementation you have now presented differs in an important way from your original description of the problem. It is now clear that the pointer involved, contentKeyCtx , is a function parameter, not a local or file-scope variable, and the code shows that it is being used to convey a pointer computed by the function back to the function's caller.

In this case, the corresponding actual argument to the function call should be the address of an appropriately-typed variable in which the function will store the generated pointer value, like so:

UInt8        *contentKeyCtx;
UInt32       contentKeyCtxSize = 0;
OSStatus     status;

status = SKDServerGenCKC(..., &contentKeyCtx, &contentKeyCtxSize);

Similar applies to the last argument, as shown; it apparently is used to return the size of the space to which the returned pointer points.

Answer 2

contentKeyCtx

没有初始化，它什么也没有指向。

Answer 3

What i am doing wrong?

There are two ways you can solve your problem:

1. Initialize contentKeyCtx :

    // Use 'calloc()', if you want it to be zero by default... UInt8 **contentKeyCtx = malloc(1, sizeof(Uint8*)); // Do something with it... 

   Or: Re-allocate it:

    UInt8 **contentKeyCtx; contentKeyCtx = realloc(NULL, sizeof(Uint8*)); // Do something with it... 

2. Use the address-of operator (aka & ):

    contentKeyCtx = &localckc;