逆向iOS SDK -- _UIImageAtPath 的实现（SDK 6.1）

汇编代码：

; 状态：R0 = imageFileName, R1 = mainBundle, R2 = isRetina       PUSH    {R4-R7,LR}; R0 = imageFileName, R1 = mainBundle, R2 = isRetina       ADD      R7, SP, #0xC       PUSH.W  {R8,R10,R11}       STR.W    R2, [SP,#0x18+var_1C]!       MOV      R4, R0  ; R4 = R0 = imageFileName       MOV      R0, #(selRef_length - 0x17BB0); selRef_length       MOV      R10, R1 ; R10 = R1 = mainBundle       ADD      R0, PC ; selRef_length       LDR      R1, [R0] ; "length"       MOV      R0, R4  ; R0 = R4 = imageFileName       BLX.W    _objc_msgSend; [imageFileName length]       MOVS     R6, #0  ; R6 = 0       CMP      R0, #0  ; check if R0 is 0       BEQ.W    loc_17D1C; if R0 is 0, goto the label       MOV      R0, R4  ; R0 = R4 = imageFileName       MOV      R1, R10 ; R1 = R10 = mainBundle       BL     __UICacheNameForImageAtPath; arg_0:imageFileName, arg_1:mainBundle, result:com.proteas.hello_Default.png       MOVW     R8, #(:lower16:(__MergedGlobals_36 - 0x17BD4))       MOV      R5, R0  ; R5 = R0 = imageCacheName       MOVT.W   R8, #(:upper16:(__MergedGlobals_36 - 0x17BD4))       ADD      R8, PC ; __MergedGlobals_36       ADD.W    R11, R8, #0x10; R11 = R8 + 16       MOV      R0, R11 ; lock, OSSpinLock*, 访问全局变量，加锁       BLX.W    _OSSpinLockLock; arg_0: OSSpinLock*       LDR.W    R0, [R8,#(dword_62C524 - 0x62C510)]; R0 = cachedImageMap, key:imageCacheName, value:UIImageObject       MOVS      R6, #0  ; R6 = 0       CBZ       R0, loc_17BEC; if cachedImageMap is nil, goto the label       MOV       R1, R5  ; R1 = R5 = imageCacheName       BLX.W _CFDictionaryGetValue; CFDictionaryGetValue(cachedImageMap, imageCacheName)       MOV       R6, R0  ; R6 = R0 = cachedUIImageObject loc_17BEC:       MOV       R0, #(selRef_retainCount - 0x17BF8); selRef_retainCount       ADD       R0, PC ; selRef_retainCount       LDR       R1, [R0]; "retainCount"       MOV       R0, R6  ; R0 = R6 = cachedUIImageObject       BLX.W     _objc_msgSend; [cachedUIImageObject retainCount]       CBNZ     R0, loc_17C08; if retainCount of cachedUIImageObject is not 0, goto the label       MOV      R0, R11 ; lock       BLX.W    _OSSpinLockUnlock       B        loc_17C50 loc_17C08:       MOV      R0, #(selRef__isCached - 0x17C14); selRef__isCached       ADD      R0, PC ; selRef__isCached       LDR      R1, [R0] ; R1 = "_isCached"       MOV      R0, R6  ; R0 = R6 = cachedUIImageObject       BLX.W    _objc_msgSend; R0 = isCached       TST.W    R0, #0xFF; check if R0 is true       BNE      loc_17C46; if not cached, goto the label       MOV      R0, #(selRef_retain - 0x17C2C); selRef_retain       ADD      R0, PC ; selRef_retain       LDR      R1, [R0] ; "retain"       MOV      R0, R6  ; R0 = R6 = cachedUIImageObject       BLX.W    _objc_msgSend; [cachedUIImageObject retain]       MOVW     R0, #(:lower16:(selRef__setCached_ - 0x17C40))       MOVS     R2, #1  ; R2 = 1       MOVT.W   R0, #(:upper16:(selRef__setCached_ - 0x17C40))       ADD      R0, PC ; selRef__setCached_       LDR      R1, [R0] ; "_setCached:"       MOV      R0, R6  ; R0 = R6 = cachedUIImageObject       BLX.W    _objc_msgSend ; [cachedUIImageObject _setCached:YES] loc_17C46:       MOV      R0, R11 ; lock       BLX.W    _OSSpinLockUnlock;释放锁       CMP      R6, #0  ; check if cachedUIImageObject is nil       BNE      loc_17D1C; if not nil, goto the label loc_17C50:       MOVW     R3, #(:lower16:(_GetImageAtPath+1 - 0x17C60))       MOV      R0, R4  ; R0 = R4 = imageFileName       MOVT.W   R3, #(:upper16:(_GetImageAtPath+1 - 0x17C60))       LDR      R2, [SP,#0x1C+var_1C]; R2 = isRetina       ADD      R3, PC ; _GetImageAtPath ; R3 = _GetImageAtPath       MOV      R1, R10 ; R1 = R10 = mainBundle       BL    __UIImageCallFunctionForAppropriatePath; arg_0:imageFileName, arg_1 = mainBundle, arg_2 = isRetina, arg_3 = _GetImageAtPath           MOV      R6, R0  ; R6 = R0 = UIImageObject       CMP      R6, #0  ; check if UIImageObject is nil       BEQ      loc_17D1C; if failed, goto label       MOV      R0, R11 ; lock       BLX.W    _OSSpinLockLock       LDR.W    R0, [R8,#0x14]; R0 = pointer to imageCacheMap       CBNZ     R0, loc_17CAE; R1 = R5 = imageCacheName       MOVW     R0, #(:lower16:(_kCFTypeDictionaryKeyCallBacks_ptr - 0x17C86))       MOVS     R1, #0  ; R1 = capacity = 0       MOVT.W R0, #(:upper16:(_kCFTypeDictionaryKeyCallBacks_ptr - 0x17C86))       MOVS     R3, #0  ; R3 = valueCallBacks = 0       ADD      R0, PC ; _kCFTypeDictionaryKeyCallBacks_ptr       LDR      R2, [R0] ; _kCFTypeDictionaryKeyCallBacks       MOVS     R0, #0  ; R0 = allocator = NULL       BLX.W    _CFDictionaryCreateMutable ; R0 = cachedImageMap       MOVW     R1, #(:lower16:(_kCFTypeDictionaryValueCallBacks_ptr - 0x17C9E))       MOVS     R2, #0  ; R2 = keyCallBacks = NULL       MOVT.W          R1, #(:upper16:(_kCFTypeDictionaryValueCallBacks_ptr - 0x17C9E))       STR.W   R0, [R8,#0x14]       ADD      R1, PC ; _kCFTypeDictionaryValueCallBacks_ptr       MOVS     R0, #0  ; R0 = allocator = NULL       LDR      R3, [R1] ; _kCFTypeDictionaryValueCallBacks       MOVS     R1, #0  ; R1 = capacity = 0       BLX.W    _CFDictionaryCreateMutable       STR.W    R0, [R8,#0x18]       LDR.W    R0, [R8,#0x14] loc_17CAE:       MOV      R1, R5  ; R1 = R5 = imageCacheName       BLX.W    _CFDictionaryContainsKey       CBNZ     R0, loc_17CF8; if has cached, goto the label       MOVW     R0, #(:lower16:(selRef__setNamed_ - 0x17CC4))       MOVS     R2, #1  ; R2 = YES       MOVT.W   R0, #(:upper16:(selRef__setNamed_ - 0x17CC4))       ADD      R0, PC ; selRef__setNamed_       LDR      R1, [R0] ; "_setNamed:"       MOV      R0, R6  ; R0 = R6 = UIImageObject       BLX.W    _objc_msgSend; [UIImageObject _setNamed:YES]       MOVW     R0, #(:lower16:(selRef__setCached_ - 0x17CD8))       MOVS     R2, #1       MOVT.W   R0, #(:upper16:(selRef__setCached_ - 0x17CD8))       ADD      R0, PC ; selRef__setCached_       LDR      R1, [R0] ; "_setCached:"       MOV      R0, R6       BLX.W   _objc_msgSend; [UIImageObject _setCached:YES]       LDR.W    R0, [R8,#0x14]; R0 = cachedImageMap       MOV      R1, R5  ; R1 = R5 = imageCacheName       MOV      R2, R6  ; R2 = R6 = UIImageObject       BLX.W   _CFDictionarySetValue; arg_0:cachedImageMap, arg_1 = imageCacheName, arg_2 = imageObject       LDR.W    R0, [R8,#0x18]       MOV      R1, R6  ; R1 = R6 = UIImageObject       MOV      R2, R5  ; R2 = R5 = imageCacheName       BLX.W  _CFDictionarySetValue; arg_0: dictionary, arg_1: imageObject, arg_2 = imageCacheName       B        loc_17D16 loc_17CF8:       MOV     R0, #(selRef_release - 0x17D04); selRef_release       ADD     R0, PC ; selRef_release       LDR     R1, [R0] ; "release"       MOV     R0, R6  ; R0 = R6 = UIImageObject       BLX.W  _objc_msgSend; [UIImageObject release]       LDR.W  R0, [R8,#0x14]; R0 = cachedImageMap       MOV    R1, R5  ; R1 = R5 = imageCacheName       BLX.W  _CFDictionaryGetValue       MOV    R6, R0  ; R6 = R0 = result UIImage instance loc_17D16:       MOV    R0, R11 ; lock       BLX.W  _OSSpinLockUnlock; release spin lock loc_17D1C:       MOV    R0, R6  ; R0 = R6 = nil       ADD    SP, SP, #4       POP.W  {R8,R10,R11}       POP     {R4-R7,PC}

 

伪代码：

 

NSDictionary *gCachedImageMapNameToImage =nil; NSDictionary *gCachedImageMapImageToName =nil; _UIImageAtPath(NSString *imageFileName,NSBundle *mainBundle,BOOL isRetina) {       if ([imageFileNamelength] ==0)            return nil;       if (gCachedImageMapNameToImage ==nil) {            gCachedImageMapNameToImage = [[NSMutableDictionaryalloc]init];            gCachedImageMapImageToName = [[NSMutableDictionaryalloc]init];       }       NSString *imageCacheName =_UICacheNameForImageAtPath(imageFileName, mainBundle);       UIImage *cachedImage = [gCachedImageMapNameToImageobjectForKey:imageCacheName];       if (cachedImage ==nil) {            cachedImage = _UIImageCallFunctionForAppropriatePath(imageFileName, mainBundle, isRetina,_UIImageAtPath);                    if (cachedImage == nil) {                  return nil;            } else {                  [gCachedImageMapNameToImagesetObject:cachedImageforKey:imageCacheName];                  [gCachedImageMapImageToNamesetObject:imageCacheNameforKey:cachedImage];                  [cachedImage _setNamed:YES];                  [cachedImage _setCached:YES];            }       } else {            if (![cachedImage _isCached]) {                  [cachedImage _setCached:YES];            }       }       return cachedImage; }