dyld_cache_format.h

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#ifndef __DYLD_CACHE_FORMAT__
#define __DYLD_CACHE_FORMAT__

#include <sys/types.h>
#include <stdint.h>
#include <mach/shared_region.h>
#include <uuid/uuid.h>


struct dyld_cache_header
{
	char		magic[16];				// e.g. "dyld_v0    i386"
	uint32_t	mappingOffset;			// file offset to first dyld_cache_mapping_info
	uint32_t	mappingCount;			// number of dyld_cache_mapping_info entries
	uint32_t	imagesOffset;			// file offset to first dyld_cache_image_info
	uint32_t	imagesCount;			// number of dyld_cache_image_info entries
	uint64_t	dyldBaseAddress;		// base address of dyld when cache was built
	uint64_t	codeSignatureOffset;	// file offset of code signature blob
	uint64_t	codeSignatureSize;		// size of code signature blob (zero means to end of file)
	uint64_t	slideInfoOffset;		// file offset of kernel slid info
	uint64_t	slideInfoSize;			// size of kernel slid info
	uint64_t	localSymbolsOffset;		// file offset of where local symbols are stored
	uint64_t	localSymbolsSize;		// size of local symbols information
	uint8_t		uuid[16];				// unique value for each shared cache file
	uint64_t	cacheType;				// 0 for development, 1 for production
	uint32_t	branchPoolsOffset;		// file offset to table of uint64_t pool addresses
	uint32_t	branchPoolsCount;	    // number of uint64_t entries
	uint64_t	accelerateInfoAddr;		// (unslid) address of optimization info
	uint64_t	accelerateInfoSize;		// size of optimization info
	uint64_t	imagesTextOffset;		// file offset to first dyld_cache_image_text_info
	uint64_t	imagesTextCount;		// number of dyld_cache_image_text_info entries
};

struct dyld_cache_mapping_info {
	uint64_t	address;
	uint64_t	size;
	uint64_t	fileOffset;
	uint32_t	maxProt;
	uint32_t	initProt;
};

struct dyld_cache_image_info
{
	uint64_t	address;
	uint64_t	modTime;
	uint64_t	inode;
	uint32_t	pathFileOffset;
	uint32_t	pad;
};

struct dyld_cache_image_info_extra
{
	uint64_t	exportsTrieAddr;		// address of trie in unslid cache
	uint64_t	weakBindingsAddr;
	uint32_t	exportsTrieSize;
	uint32_t	weakBindingsSize;
	uint32_t	dependentsStartArrayIndex;
	uint32_t	reExportsStartArrayIndex;
};


struct dyld_cache_accelerator_info
{
	uint32_t	version;				// currently 1
	uint32_t	imageExtrasCount;		// does not include aliases
	uint32_t	imagesExtrasOffset;		// offset into this chunk of first dyld_cache_image_info_extra
	uint32_t	bottomUpListOffset;		// offset into this chunk to start of 16-bit array of sorted image indexes
	uint32_t	dylibTrieOffset;		// offset into this chunk to start of trie containing all dylib paths
	uint32_t	dylibTrieSize;			// size of trie containing all dylib paths
	uint32_t	initializersOffset;		// offset into this chunk to start of initializers list
	uint32_t	initializersCount;		// size of initializers list
	uint32_t	dofSectionsOffset;		// offset into this chunk to start of DOF sections list
	uint32_t	dofSectionsCount;		// size of initializers list
	uint32_t	reExportListOffset;		// offset into this chunk to start of 16-bit array of re-exports
	uint32_t	reExportCount;			// size of re-exports
	uint32_t	depListOffset;			// offset into this chunk to start of 16-bit array of dependencies (0x8000 bit set if upward)
	uint32_t	depListCount;			// size of dependencies
	uint32_t	rangeTableOffset;		// offset into this chunk to start of ss
	uint32_t	rangeTableCount;		// size of dependencies
	uint64_t	dyldSectionAddr;		// address of libdyld's __dyld section in unslid cache
};

struct dyld_cache_accelerator_initializer
{
	uint32_t	functionOffset;			// address offset from start of cache mapping
	uint32_t	imageIndex;
};

struct dyld_cache_range_entry
{
	uint64_t	startAddress;			// unslid address of start of region
	uint32_t	size;
	uint32_t	imageIndex;
};

struct dyld_cache_accelerator_dof
{
	uint64_t	sectionAddress;			// unslid address of start of region
	uint32_t	sectionSize;
	uint32_t	imageIndex;
};

struct dyld_cache_image_text_info
{
	uuid_t		uuid;
	uint64_t	loadAddress;			// unslid address of start of __TEXT
	uint32_t	textSegmentSize;
	uint32_t	pathOffset;				// offset from start of cache file
};


// The rebasing info is to allow the kernel to lazily rebase DATA pages of the
// dyld shared cache.  Rebasing is adding the slide to interior pointers.
struct dyld_cache_slide_info
{
	uint32_t	version;		// currently 1
	uint32_t	toc_offset;
	uint32_t	toc_count;
	uint32_t	entries_offset;
	uint32_t	entries_count;
	uint32_t	entries_size;  // currently 128 
	// uint16_t toc[toc_count];
	// entrybitmap entries[entries_count];
};


// The version 2 of the slide info uses a different compression scheme. Since
// only interior pointers (pointers that point within the cache) are rebased
// (slid), we know the possible range of the pointers and thus know there are
// unused bits in each pointer.  We use those bits to form a linked list of
// locations needing rebasing in each page.
//
// Definitions:
//
//  pageIndex = (pageAddress - startOfAllDataAddress)/info->page_size
//  pageStarts[] = info + info->page_starts_offset
//  pageExtras[] = info + info->page_extras_offset
//  valueMask = ~(info->delta_mask)
//  deltaShift = __builtin_ctzll(info->delta_mask) - 2
//
// There are three cases:
//
// 1) pageStarts[pageIndex] == DYLD_CACHE_SLIDE_PAGE_ATTR_NO_REBASE
//    The page contains no values that need rebasing.
//
// 2) (pageStarts[pageIndex] & DYLD_CACHE_SLIDE_PAGE_ATTR_EXTRA) == 0
//    All rebase locations are in one linked list. The offset of the first
//    rebase location in the page is pageStarts[pageIndex] * 4.
//
// 3) pageStarts[pageIndex] & DYLD_CACHE_SLIDE_PAGE_ATTR_EXTRA
//	  Multiple linked lists are needed for all rebase locations in a page.
//    The pagesExtras array contains 2 or more entries each of which is the
//    start of a new linked list in the page. The first is at:
//       extrasStartIndex = (pageStarts[pageIndex] & 0x3FFF)
//	  The next is at extrasStartIndex+1.  The last is denoted by
//    having the high bit (DYLD_CACHE_SLIDE_PAGE_ATTR_END) of the pageExtras[]
//    set.
//
// For 64-bit architectures, there is always enough free bits to encode all
// possible deltas.  The info->delta_mask field shows where the delta is located
// in the pointer.  That value must be masked off (valueMask) before the slide
// is added to the pointer.
//
// For 32-bit architectures, there are only three bits free (the three most
// significant bits). To extract the delta, you must first subtract value_add
// from the pointer value, then AND with delta_mask, then shift by deltaShift.
// That still leaves a maximum delta to the next rebase location of 28 bytes.
// To reduce the number or chains needed, an optimization was added.  Turns
// out zero is common in the DATA region.  A zero can be turned into a
// non-rebasing entry in the linked list.  The can be done because nothing
// in the shared cache should point out of its dylib to the start of the shared
// cache.
//
// The code for processing a linked list (chain) is:
//   
//	uint32_t delta = 1;
//	while ( delta != 0 ) {
//		uint8_t* loc = pageStart + pageOffset;
//		uintptr_t rawValue = *((uintptr_t*)loc);
//		delta = ((rawValue & deltaMask) >> deltaShift);
//		uintptr_t newValue = (rawValue & valueMask);
//		if ( newValue != 0 ) {
//			newValue += valueAdd;
//			newValue += slideAmount;
//		}
//		*((uintptr_t*)loc) = newValue;
//		pageOffset += delta;
//	}
//
//
struct dyld_cache_slide_info2
{
	uint32_t	version;		// currently 2
	uint32_t	page_size;		// currently 4096 (may also be 16384)
	uint32_t	page_starts_offset;
	uint32_t	page_starts_count;
	uint32_t	page_extras_offset;
	uint32_t	page_extras_count;
	uint64_t	delta_mask;		// which (contiguous) set of bits contains the delta to the next rebase location
	uint64_t	value_add;
	//uint16_t	page_starts[page_starts_count];
	//uint16_t	page_extras[page_extras_count];
};
#define DYLD_CACHE_SLIDE_PAGE_ATTRS				0xC000	// high bits of uint16_t are flags
#define DYLD_CACHE_SLIDE_PAGE_ATTR_EXTRA		0x8000  // index is into extras array (not starts array)
#define DYLD_CACHE_SLIDE_PAGE_ATTR_NO_REBASE	0x4000  // page has no rebasing
#define DYLD_CACHE_SLIDE_PAGE_ATTR_END			0x8000  // last chain entry for page


struct dyld_cache_local_symbols_info
{
	uint32_t	nlistOffset;		// offset into this chunk of nlist entries
	uint32_t	nlistCount;			// count of nlist entries
	uint32_t	stringsOffset;		// offset into this chunk of string pool
	uint32_t	stringsSize;		// byte count of string pool
	uint32_t	entriesOffset;		// offset into this chunk of array of dyld_cache_local_symbols_entry 
	uint32_t	entriesCount;		// number of elements in dyld_cache_local_symbols_entry array
};

struct dyld_cache_local_symbols_entry
{
	uint32_t	dylibOffset;		// offset in cache file of start of dylib
	uint32_t	nlistStartIndex;	// start index of locals for this dylib
	uint32_t	nlistCount;			// number of local symbols for this dylib
};



#define MACOSX_DYLD_SHARED_CACHE_DIR	"/private/var/db/dyld/"
#define IPHONE_DYLD_SHARED_CACHE_DIR	"/System/Library/Caches/com.apple.dyld/"
#define DYLD_SHARED_CACHE_BASE_NAME		"dyld_shared_cache_"
#define DYLD_SHARED_CACHE_DEVELOPMENT_EXT ".development"

static const uint64_t kDyldSharedCacheTypeDevelopment = 0;
static const uint64_t kDyldSharedCacheTypeProduction = 1;




#endif // __DYLD_CACHE_FORMAT__