I’m working with the EXIF library at http://code.google.com/p/iphone-exif/ and I have come across a real head scratcher of a bug. When I implement the library in a debug build everything works beautifully, but when I compile for ad hoc beta testing the app crashes hard.
I’m getting the following error:
Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x00000000
Crashed Thread: 5
With Thread 5:
0 Gaia GPS 0x000494e4 -[EXFJpeg scanImageData:] (EXFJpeg.m:372)
1 Gaia GPS 0x0000524c -[MyAppDelegate saveImage:] (MyAppDelegate.m:935)
2 Foundation 0x317fef32 0x317ad000 + 335666
3 Foundation 0x317ae09a 0x317ad000 + 4250
4 libSystem.B.dylib 0x329c892a 0x329a4000 + 149802
It is my suspicion that there is something different about the way the debug build handles memory vs. the way the ad-hoc build handles memory. It seems to me from the error that this code is trying to write to memory blocks it does not have access to, and when it does the Ad-hoc iPhone OS shuts the process down.
What would cause this behavior in the ad hoc distribution, but not in the debug build? The debug build works fine even when the phone is disconnected and the debugger off.
Many thanks in advance.
The code:
My Code to implement the library (Line 935 is the first line of this block, the alloc statment)
:
EXFJpeg* jpegScanner = [[EXFJpeg alloc] init];
[jpegScanner scanImageData:imgData];
CLLocation *location = self.gps.lastReading ? self.gps.lastReading : [self.gps.locationManager location];
[location retain];
NSMutableArray* locArray = [self createLocArray:location.coordinate.latitude];
EXFGPSLoc* gpsLoc = [[EXFGPSLoc alloc] init];
[self populateGPS: gpsLoc :locArray];
[jpegScanner.exifMetaData addTagValue:gpsLoc forKey:[NSNumber numberWithInt:EXIF_GPSLatitude];
[gpsLoc release];
locArray = [self createLocArray:location.coordinate.longitude];
gpsLoc = [[EXFGPSLoc alloc] init];
[self populateGPS: gpsLoc :locArray];
[locArray release];
[jpegScanner.exifMetaData addTagValue:gpsLoc forKey:[NSNumber numberWithInt:EXIF_GPSLongitude];
[gpsLoc release];
NSString *ref = (location.coordinate.latitude <0.0)?ref = @"S": @"N";
[jpegScanner.exifMetaData addTagValue: ref forKey:[NSNumber numberWithInt:EXIF_GPSLatitudeRef] ];
ref = (location.coordinate.longitude <0.0)? @"W": @"E";
[jpegScanner.exifMetaData addTagValue: ref forKey:[NSNumber numberWithInt:EXIF_GPSLongitudeRef]];
[jpegScanner.exifMetaData addTagValue: @"Apple" forKey:[NSNumber numberWithInt:EXIF_Make];
[jpegScanner.exifMetaData addTagValue: @"iPhone" forKey:NSNumber numberWithInt:EXIF_Model];
[jpegScanner.exifMetaData addTagValue:[NSNumber numberWithInt:0] forKey:[NSNumber numberWithInt:EXIF_GPSAltitudeRef] ];
NSArray *arr = [[NSArray alloc] initWithObjects:[NSNumber numberWithInt:0], NSNumber numberWithInt:0], [NSNumber numberWithInt:2], [NSNumber numberWithInt:2], nil];
[jpegScanner.exifMetaData addTagValue: arr forKey:[NSNumber numberWithInt:EXIF_GPSVersion] ];
[arr release];
long numDenumArray[2];
long* arrPtr = numDenumArray;
[EXFUtils convertRationalToFraction:&arrPtr: [NSNumber numberWithDouble:location.altitude]];
EXFraction *fract = [[EXFraction alloc] initWith:numDenumArray[0] :numDenumArray[1]];
[jpegScanner.exifMetaData addTagValue:fract forKey:[NSNumber
numberWithInt:EXIF_GPSAltitude] ];
NSMutableData *newData = [[NSMutableData alloc] init];
[jpegScanner populateImageData:newData];
[jpegScanner release];
And last but not lest the function from the library itself:
-(void) scanImageData: (NSData*) jpegData {
Debug(@"Starting scan headers");
// pointer to the end of the EXIF Data and the start of the rest of the image
ByteArray* endOfEXFPtr;
imageLength = CFDataGetLength((CFDataRef)jpegData);
// CFRetain(&imageLength);
Debug(@"Length of image %i", imageLength);
imageBytePtr = (UInt8 *) CFDataGetBytePtr((CFDataRef)jpegData);
imageStartPtr = imageBytePtr;
// check if a valid jpeg file
UInt8 val = [self readNextbyte];
if (val != M_BEG){
Debug(@"Not a valid JPEG File");
return;
}
val = [self readNextbyte];
if (val != M_SOI){
Debug(@"Not a valid start of image JPEG File");
return;
}
// increment this to position after second byte
BOOL finished =FALSE;
while(!finished){
// increment the marker
val = [self nextMarker];
Debug(@"Got next marker %x at byte count %i", val, (imageBytePtr - imageStartPtr));
switch(val){
case M_SOF0: /* Baseline */
case M_SOF1: /* Extended sequential, Huffman */
case M_SOF2: /* Progressive, Huffman */
case M_SOF3: /* Lossless, Huffman */
case M_SOF5: /* Differential sequential, Huffman */
case M_SOF6: /* Differential progressive, Huffman */
case M_SOF7: /* Differential lossless, Huffman */
case M_SOF9: /* Extended sequential, arithmetic */
case M_SOF10: /* Progressive, arithmetic */
case M_SOF11: /* Lossless, arithmetic */
case M_SOF13: /* Differential sequential, arithmetic */
case M_SOF14: /* Differential progressive, arithmetic */
case M_SOF15: /* Differential lossless, arithmetic */
// Remember the kind of compression we saw
{
int compression = *imageBytePtr; // <-----------LINE 372
self.exifMetaData.compression = compression;
// Get the intrinsic properties fo the image
[self readImageInfo];
}
break;
case M_SOS: /* stop before hitting compressed data */
Debug(@"Found SOS at %i", imageBytePtr - imageStartPtr);
// [self skipVariable];
// Update the EXIF
// updateExif();
finished = TRUE;
break;
case M_EOI: /* in case it's a tables-only JPEG stream */
Debug(@"End of Image reached at %i ", imageBytePtr - imageStartPtr);
finished =TRUE;
break;
case M_COM:
Debug(@"Got com at %i",imageBytePtr - imageStartPtr);
break;
case M_APP0:
case M_APP1:
case M_APP2:
case M_APP3:
case M_APP4:
case M_APP5:
case M_APP6:
case M_APP7:
case M_APP8:
case M_APP9:
case M_APP10:
case M_APP11:
case M_APP12:
case M_APP13:
case M_APP14:
case M_APP15:
// Some digital camera makers put useful textual
// information into APP1 and APP12 markers, so we print
// those out too when in -verbose mode.
{
Debug(@"Found app %x at %i", val, imageBytePtr - imageStartPtr);
NSData* commentData = [self processComment];
NSNumber* key = [[NSNumber alloc]initWithInt:val];
// add comments to dictionary
[self.keyedHeaders setObject:commentData forKey:key];
[key release];
// will always mark the end of the app_x block
endOfEXFPtr = imageBytePtr;
// we pass a pointer to the NSData pointer here
if (val == M_APP0){
Debug(@"Parsing JFIF APP_0 at %i", imageBytePtr - imageStartPtr);
[self parseJfif:(CFDataRef*)&commentData];
} else if (val == M_APP1){
[self parseExif:(CFDataRef*)&commentData];
Debug(@"Finished App1 at %i", endOfEXFPtr - imageStartPtr);
} else if (val == M_APP2){
Debug(@"Finished APP2 at %i", imageBytePtr - imageStartPtr);
}else{
Debug(@"Finished App &x at %i", val, imageBytePtr - imageStartPtr);
}
}
break;
case M_SOI:
Debug(@"SOI encountered at %i",imageBytePtr - imageStartPtr);
break;
default: // Anything else just gets skipped
Debug(@"NOt handled %x skipping at %i",val, imageBytePtr - imageStartPtr);
[self skipVariable]; // we assume it has a parameter count...
break;
}
}
// add in the bytes after the exf block
NSData* theRemainingdata = [[NSData alloc] initWithBytes:endOfEXFPtr length:imageLength - (endOfEXFPtr - imageStartPtr)];
self.remainingData = theRemainingdata;
[theRemainingdata release];
endOfEXFPtr = NULL;
imageStartPtr = NULL;
imageBytePtr = NULL;
}
I got this same problem a while ago, and found 2 solutions (or workarounds):
Use the precompiled library from http://code.google.com/p/iphone-exif/downloads/list instead of compiling from the source
Change line 1270 of EXFMetaData.m to:
CFDataGetBytes(*exifData, CFRangeMake(6,2), order);
as suggested here: http://code.google.com/p/iphone-exif/issues/detail?id=4&can=1