[原]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 ([imageFileName length] == 0)

returnnil;

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) {

returnnil;

} else {

[gCachedImageMapNameToImagesetObject:cachedImage forKey:imageCacheName];

[gCachedImageMapImageToNamesetObject:imageCacheName forKey:cachedImage];

[cachedImage _setNamed:YES];

[cachedImage _setCached:YES];

}

} else {

if (![cachedImage _isCached]) {

[cachedImage _setCached:YES];

}

}

return cachedImage;

}