Objects in memory

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CFRuntimeClass

CF* objekti potiču iz CoreFOundation-a, koji pruža više od 50 klasa objekata poput CFString, CFNumber ili CFAllocatior.

Sve ove klase su instance klase CFRuntimeClass, koja kada se pozove vraća indeks u __CFRuntimeClassTable. CFRuntimeClass je definisan u CFRuntime.h:

// Some comments were added to the original code

enum { // Version field constants
_kCFRuntimeScannedObject =     (1UL << 0),
_kCFRuntimeResourcefulObject = (1UL << 2),  // tells CFRuntime to make use of the reclaim field
_kCFRuntimeCustomRefCount =    (1UL << 3),  // tells CFRuntime to make use of the refcount field
_kCFRuntimeRequiresAlignment = (1UL << 4),  // tells CFRuntime to make use of the requiredAlignment field
};

typedef struct __CFRuntimeClass {
CFIndex version;  // This is made a bitwise OR with the relevant previous flags

const char *className; // must be a pure ASCII string, nul-terminated
void (*init)(CFTypeRef cf);  // Initializer function
CFTypeRef (*copy)(CFAllocatorRef allocator, CFTypeRef cf); // Copy function, taking CFAllocatorRef and CFTypeRef to copy
void (*finalize)(CFTypeRef cf); // Finalizer function
Boolean (*equal)(CFTypeRef cf1, CFTypeRef cf2); // Function to be called by CFEqual()
CFHashCode (*hash)(CFTypeRef cf); // Function to be called by CFHash()
CFStringRef (*copyFormattingDesc)(CFTypeRef cf, CFDictionaryRef formatOptions); // Provides a CFStringRef with a textual description of the object// return str with retain
CFStringRef (*copyDebugDesc)(CFTypeRef cf);	// CFStringRed with textual description of the object for CFCopyDescription

#define CF_RECLAIM_AVAILABLE 1
void (*reclaim)(CFTypeRef cf); // Or in _kCFRuntimeResourcefulObject in the .version to indicate this field should be used
// It not null, it's called when the last reference to the object is released

#define CF_REFCOUNT_AVAILABLE 1
// If not null, the following is called when incrementing or decrementing reference count
uint32_t (*refcount)(intptr_t op, CFTypeRef cf); // Or in _kCFRuntimeCustomRefCount in the .version to indicate this field should be used
// this field must be non-NULL when _kCFRuntimeCustomRefCount is in the .version field
// - if the callback is passed 1 in 'op' it should increment the 'cf's reference count and return 0
// - if the callback is passed 0 in 'op' it should return the 'cf's reference count, up to 32 bits
// - if the callback is passed -1 in 'op' it should decrement the 'cf's reference count; if it is now zero, 'cf' should be cleaned up and deallocated (the finalize callback above will NOT be called unless the process is running under GC, and CF does not deallocate the memory for you; if running under GC, finalize should do the object tear-down and free the object memory); then return 0
// remember to use saturation arithmetic logic and stop incrementing and decrementing when the ref count hits UINT32_MAX, or you will have a security bug
// remember that reference count incrementing/decrementing must be done thread-safely/atomically
// objects should be created/initialized with a custom ref-count of 1 by the class creation functions
// do not attempt to use any bits within the CFRuntimeBase for your reference count; store that in some additional field in your CF object

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wmissing-field-initializers"
#define CF_REQUIRED_ALIGNMENT_AVAILABLE 1
// If not 0, allocation of object must be on this boundary
uintptr_t requiredAlignment; // Or in _kCFRuntimeRequiresAlignment in the .version field to indicate this field should be used; the allocator to _CFRuntimeCreateInstance() will be ignored in this case; if this is less than the minimum alignment the system supports, you'll get higher alignment; if this is not an alignment the system supports (e.g., most systems will only support powers of two, or if it is too high), the result (consequences) will be up to CF or the system to decide

} CFRuntimeClass;

Objective-C

Korišćeni delovi memorije

Većina podataka koje koristi ObjectiveC tokom izvršavanja će se menjati, stoga koristi neke sekcije iz __DATA segmenta u memoriji:

• __objc_msgrefs (message_ref_t): Reference poruka

• __objc_ivar (ivar): Instance promenljive

• __objc_data (...): Promenljivi podaci

• __objc_classrefs (Class): Reference klasa

• __objc_superrefs (Class): Reference nadklasa

• __objc_protorefs (protocol_t *): Reference protokola

• __objc_selrefs (SEL): Reference selektora

• __objc_const (...): Klasni r/o podaci i drugi (nadam se) konstantni podaci

• __objc_imageinfo (version, flags): Korišćeno tokom učitavanja slike: Trenutna verzija je 0; Zastave specificiraju preoptimizovanu podršku za GC, itd.

• __objc_protolist (protocol_t *): Lista protokola

• __objc_nlcatlist (category_t): Pokazivač na Non-Lazy kategorije definisane u ovom binarnom fajlu

• __objc_catlist (category_t): Pokazivač na kategorije definisane u ovom binarnom fajlu

• __objc_nlclslist (classref_t): Pokazivač na Non-Lazy Objective-C klase definisane u ovom binarnom fajlu

• __objc_classlist (classref_t): Pokazivači na sve Objective-C klase definisane u ovom binarnom fajlu

Takođe koristi nekoliko sekcija u __TEXT segmentu da bi sačuvao konstantne vrednosti ako nije moguće pisati u ovu sekciju:

• __objc_methname (C-String): Imena metoda

• __objc_classname (C-String): Imena klasa

• __objc_methtype (C-String): Tipovi metoda

Kodiranje tipova

Objective-C koristi neko prepravljanje za enkodiranje selektora i tipova promenljivih jednostavnih i složenih tipova:

• Primitivni tipovi koriste prvo slovo tipa i za int, c za char, l za long... i koristi veliko slovo u slučaju da je unsigned (L za unsigned Long).

• Ostali tipovi podataka čija su slova već zauzeta ili su specijalna, koriste druga slova ili simbole poput q za long long, b za bitfields, B za booleans, # za classes, @ za id, * za char pokazivače, ^ za generičke pokazivače i ? za nedefinisane.

• Nizovi, strukture i unije koriste [, { i (

Primer Deklaracije Metoda

- (NSString *)processString:(id)input withOptions:(char *)options andError:(id)error;

Selektor bi bio processString:withOptions:andError:

Kodiranje tipa

• id je kodiran kao @

• char * je kodiran kao *

Potpuno kodiranje tipa za metod je:

@24@0:8@16*20^@24

Detaljna analiza

1. Tip povratne vrednosti (NSString *): Kodiran kao @ sa dužinom 24

2. self (instanca objekta): Kodirano kao @, na offsetu 0

3. _cmd (selektor): Kodiran kao :, na offsetu 8

4. Prvi argument (char * input): Kodiran kao *, na offsetu 16

5. Drugi argument (NSDictionary * options): Kodiran kao @, na offsetu 20

6. Treći argument (NSError ** error): Kodiran kao ^@, na offsetu 24

Sa selektorom + kodiranjem možete rekonstruisati metod.

Klase

Klase u Objective-C-u su struktura sa svojstvima, pokazivačima na metode... Moguće je pronaći strukturu objc_class u izvornom kodu:

struct objc_class : objc_object {
// Class ISA;
Class superclass;
cache_t cache;             // formerly cache pointer and vtable
class_data_bits_t bits;    // class_rw_t * plus custom rr/alloc flags

class_rw_t *data() {
return bits.data();
}
void setData(class_rw_t *newData) {
bits.setData(newData);
}

void setInfo(uint32_t set) {
assert(isFuture()  ||  isRealized());
data()->setFlags(set);
}
[...]

Ova klasa koristi neke bitove polja isa da bi označila informacije o klasi.

Zatim, struktura ima pokazivač na strukturu class_ro_t koja je smeštena na disku i sadrži atribute klase poput njenog imena, osnovnih metoda, svojstava i instanci varijabli. Tokom izvršavanja, dodatna struktura class_rw_t se koristi koja sadrži pokazivače koji mogu biti promenjeni poput metoda, protokola, svojstava...