More refactoring.
theraven
16 years ago
parent
2d84b96a72
commit
7b8b3839df
@ -0,0 +1,105 @@
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#include <stdio.h>
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#include <stdlib.h>
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#include <objc/runtime.h>
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#include "class.h"
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#include "ivar.h"
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ptrdiff_t objc_alignof_type(const char *);
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ptrdiff_t objc_sizeof_type(const char *);
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void __objc_compute_ivar_offsets(Class class)
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{
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int i = 0;
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/* If this class was compiled with support for late-bound ivars, the
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* instance_size field will contain 0 - {the size of the instance variables
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* declared for just this class}. The individual instance variable offset
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* fields will then be the offsets from the start of the class, and so must
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* have the size of the parent class prepended. */
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if (class->instance_size <= 0)
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{
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Class super = class_getSuperclass(class);
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long ivar_start = 0;
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if (Nil != super)
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{
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if (super->instance_size <= 0)
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{
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__objc_compute_ivar_offsets(super);
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}
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ivar_start = super->instance_size;
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}
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class->instance_size = ivar_start - class->instance_size;
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/* For each instance variable, we add the offset if required (it will be zero
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* if this class is compiled with a static ivar layout). We then set the
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* value of a global variable to the offset value.
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*
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* Any class compiled with support for the non-fragile ABI, but not actually
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* using it, will export the ivar offset field as a symbol.
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*
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* Note that using non-fragile ivars breaks @defs(). If you need equivalent
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* functionality, provide an alternative @interface with all variables
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* declared @public.
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*/
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if (class->ivars)
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{
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for (i = 0 ; i < class->ivars->count ; i++)
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{
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struct objc_ivar *ivar = &class->ivars->ivar_list[i];
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ivar->offset += ivar_start;
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/* If we're using the new ABI then we also set up the faster ivar
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* offset variables.
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*/
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if (objc_test_class_flag(class, objc_class_flag_new_abi))
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{
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*(class->ivar_offsets[i]) = ivar->offset;
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}
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}
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}
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}
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else
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{
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if (NULL == class->ivars) { return; }
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Class super = class_getSuperclass(class);
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int start = class->ivars->ivar_list[0].offset;
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/* Quick and dirty test. If the first ivar comes straight after the last
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* class, then it's fine. */
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if (Nil == super || start == super->instance_size) {return; }
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/* Find the last superclass with at least one ivar. */
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while (NULL == super->ivars)
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{
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super = class_getSuperclass(super);
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}
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struct objc_ivar *ivar =
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&super->ivars->ivar_list[super->ivars->count-1];
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if (start == (ivar->offset + objc_sizeof_type(ivar->type)))
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{
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return;
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}
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/* The classes don't line up, but don't panic; check that the
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* difference is not just padding for alignment */
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int align = objc_alignof_type(class->ivars->ivar_list[0].type);
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if (start > ivar->offset && start - ivar->offset < align)
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{
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return;
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}
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/* Panic if this class has an instance variable that overlaps the
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* superclass. */
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fprintf(stderr,
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"Error: Instance variables in %s overlap superclass %s. ",
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class->name, super->name);
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fprintf(stderr,
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"Offset of first instance variable, %s, is %d. ",
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class->ivars->ivar_list[0].name, start);
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fprintf(stderr,
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"Last instance variable in superclass, %s, ends at offset %d. ",
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ivar->name, ivar->offset +
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objc_sizeof_type(ivar->type));
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fprintf(stderr, "This probably means that you are subclassing a"
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"class from a library, which has changed in a binary-incompatible"
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"way.\n");
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abort();
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}
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}
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@ -0,0 +1,47 @@
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/**
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* Metadata structure for an instance variable.
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*
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* Note: The modern Apple runtime apparently stores the alignment of the ivar
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* here. We don't - we can compute it from the type, but it might be useful.
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*
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* It would also be good to add GC properties to this structure, and possibly
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* an assignment policy (e.g. assign / retain / copy).
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*/
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struct objc_ivar
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{
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/**
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* Name of this instance variable.
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*/
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const char *name;
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/**
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* Type encoding for this instance variable.
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*/
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const char *type;
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/**
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* The offset from the start of the object. When using the non-fragile
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* ABI, this is initialized by the compiler to the offset from the start of
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* the ivars declared by this class. It is then set by the runtime to the
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* offset from the object pointer.
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*/
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int offset;
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};
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/**
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* A list of instance variables declared on this class. Unlike the method
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* list, this is a single array and size. Categories are not allowed to add
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* instance variables, because that would require existing objects to be
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* reallocated, which is only possible with accurate GC (i.e. not in C).
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*/
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struct objc_ivar_list
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{
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/**
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* The number of instance variables in this list.
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*/
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int count;
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/**
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* An array of instance variable metadata structures. Note that this array
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* has count elements, not 1.
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*/
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struct objc_ivar ivar_list[1];
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};
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