/* * Copyright (c) 2004-2008 Apple Inc. All rights reserved. * * @APPLE_LICENSE_HEADER_START@ * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this * file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_LICENSE_HEADER_END@ */ #include #include #include "objc-private.h" /********************************************************************** * Object Layouts. * * Layouts are used by the garbage collector to identify references from * the object to other objects. * * Layout information is in the form of a '\0' terminated byte string. * Each byte contains a word skip count in the high nibble and a * consecutive references count in the low nibble. Counts that exceed 15 are * continued in the succeeding byte with a zero in the opposite nibble. * Objects that should be scanned conservatively will have a NULL layout. * Objects that have no references have a empty byte string. * * Example; * * For a class with pointers at offsets 4,12, 16, 32-128 * the layout is { 0x11, 0x12, 0x3f, 0x0a, 0x00 } or * skip 1 - 1 reference (4) * skip 1 - 2 references (12, 16) * skip 3 - 15 references (32-88) * no skip - 10 references (92-128) * end * **********************************************************************/ /********************************************************************** * compress_layout * Allocates and returns a compressed string matching the given layout bitmap. **********************************************************************/ static unsigned char * compress_layout(const uint8_t *bits, size_t bitmap_bits, bool weak) { bool all_set = YES; bool none_set = YES; unsigned char *result; // overallocate a lot; reallocate at correct size later unsigned char * const layout = (unsigned char *) calloc(bitmap_bits + 1, 1); unsigned char *l = layout; size_t i = 0; while (i < bitmap_bits) { size_t skip = 0; size_t scan = 0; // Count one range each of skip and scan. while (i < bitmap_bits) { uint8_t bit = (uint8_t)((bits[i/8] >> (i % 8)) & 1); if (bit) break; i++; skip++; } while (i < bitmap_bits) { uint8_t bit = (uint8_t)((bits[i/8] >> (i % 8)) & 1); if (!bit) break; i++; scan++; none_set = NO; } // Record skip and scan if (skip) all_set = NO; if (scan) none_set = NO; while (skip > 0xf) { *l++ = 0xf0; skip -= 0xf; } if (skip || scan) { *l = (uint8_t)(skip << 4); // NOT incremented - merges with scan while (scan > 0xf) { *l++ |= 0x0f; // May merge with short skip; must calloc scan -= 0xf; } *l++ |= scan; // NOT checked for zero - always increments // May merge with short skip; must calloc } } // insert terminating byte *l++ = '\0'; // return result if (none_set && weak) { result = NULL; // NULL weak layout means none-weak } else if (all_set && !weak) { result = NULL; // NULL ivar layout means all-scanned } else { result = (unsigned char *)strdup((char *)layout); } free(layout); return result; } static void set_bits(layout_bitmap bits, size_t which, size_t count) { // fixme optimize for byte/word at a time size_t bit; for (bit = which; bit < which + count && bit < bits.bitCount; bit++) { bits.bits[bit/8] |= 1 << (bit % 8); } if (bit == bits.bitCount && bit < which + count) { // couldn't fit full type in bitmap _objc_fatal("layout bitmap too short"); } } static void clear_bits(layout_bitmap bits, size_t which, size_t count) { // fixme optimize for byte/word at a time size_t bit; for (bit = which; bit < which + count && bit < bits.bitCount; bit++) { bits.bits[bit/8] &= ~(1 << (bit % 8)); } if (bit == bits.bitCount && bit < which + count) { // couldn't fit full type in bitmap _objc_fatal("layout bitmap too short"); } } static void move_bits(layout_bitmap bits, size_t src, size_t dst, size_t count) { // fixme optimize for byte/word at a time if (dst == src) { return; } else if (dst > src) { // Copy backwards in case of overlap size_t pos = count; while (pos--) { size_t srcbit = src + pos; size_t dstbit = dst + pos; if (bits.bits[srcbit/8] & (1 << (srcbit % 8))) { bits.bits[dstbit/8] |= 1 << (dstbit % 8); } else { bits.bits[dstbit/8] &= ~(1 << (dstbit % 8)); } } } else { // Copy forwards in case of overlap size_t pos; for (pos = 0; pos < count; pos++) { size_t srcbit = src + pos; size_t dstbit = dst + pos; if (bits.bits[srcbit/8] & (1 << (srcbit % 8))) { bits.bits[dstbit/8] |= 1 << (dstbit % 8); } else { bits.bits[dstbit/8] &= ~(1 << (dstbit % 8)); } } } } // emacs autoindent hack - it doesn't like the loop in set_bits/clear_bits #if 0 } } #endif static void decompress_layout(const unsigned char *layout_string, layout_bitmap bits) { unsigned char c; size_t bit = 0; while ((c = *layout_string++)) { unsigned char skip = (c & 0xf0) >> 4; unsigned char scan = (c & 0x0f); bit += skip; set_bits(bits, bit, scan); bit += scan; } } /*********************************************************************** * layout_bitmap_create * Allocate a layout bitmap. * The new bitmap spans the given instance size bytes. * The start of the bitmap is filled from the given layout string (which * spans an instance size of layoutStringSize); the rest is zero-filled. * The returned bitmap must be freed with layout_bitmap_free(). **********************************************************************/ layout_bitmap layout_bitmap_create(const unsigned char *layout_string, size_t layoutStringInstanceSize, size_t instanceSize, bool weak) { layout_bitmap result; size_t words = instanceSize / sizeof(id); result.weak = weak; result.bitCount = words; result.bitsAllocated = words; result.bits = (uint8_t *)calloc((words+7)/8, 1); if (!layout_string) { if (!weak) { // NULL ivar layout means all-scanned // (but only up to layoutStringSize instance size) set_bits(result, 0, layoutStringInstanceSize/sizeof(id)); } else { // NULL weak layout means none-weak. } } else { decompress_layout(layout_string, result); } return result; } /*********************************************************************** * layout_bitmap_create_empty * Allocate a layout bitmap. * The new bitmap spans the given instance size bytes. * The bitmap is empty, to represent an object whose ivars are completely unscanned. * The returned bitmap must be freed with layout_bitmap_free(). **********************************************************************/ layout_bitmap layout_bitmap_create_empty(size_t instanceSize, bool weak) { layout_bitmap result; size_t words = instanceSize / sizeof(id); result.weak = weak; result.bitCount = words; result.bitsAllocated = words; result.bits = (uint8_t *)calloc((words+7)/8, 1); return result; } void layout_bitmap_free(layout_bitmap bits) { if (bits.bits) free(bits.bits); } const unsigned char * layout_string_create(layout_bitmap bits) { const unsigned char *result = compress_layout(bits.bits, bits.bitCount, bits.weak); #if DEBUG // paranoia: cycle to bitmap and back to string again, and compare layout_bitmap check = layout_bitmap_create(result, bits.bitCount*sizeof(id), bits.bitCount*sizeof(id), bits.weak); unsigned char *result2 = compress_layout(check.bits, check.bitCount, check.weak); if (result != result2 && 0 != strcmp((char*)result, (char *)result2)) { layout_bitmap_print(bits); layout_bitmap_print(check); _objc_fatal("libobjc bug: mishandled layout bitmap"); } free(result2); layout_bitmap_free(check); #endif return result; } void layout_bitmap_set_ivar(layout_bitmap bits, const char *type, size_t offset) { // fixme only handles some types size_t bit = offset / sizeof(id); if (!type) return; if (type[0] == '@' || 0 == strcmp(type, "^@")) { // id // id * // Block ("@?") set_bits(bits, bit, 1); } else if (type[0] == '[') { // id[] char *t; unsigned long count = strtoul(type+1, &t, 10); if (t && t[0] == '@') { set_bits(bits, bit, count); } } else if (strchr(type, '@')) { _objc_inform("warning: failing to set GC layout for '%s'\n", type); } } /*********************************************************************** * layout_bitmap_grow * Expand a layout bitmap to span newCount bits. * The new bits are undefined. **********************************************************************/ void layout_bitmap_grow(layout_bitmap *bits, size_t newCount) { if (bits->bitCount >= newCount) return; bits->bitCount = newCount; if (bits->bitsAllocated < newCount) { size_t newAllocated = bits->bitsAllocated * 2; if (newAllocated < newCount) newAllocated = newCount; bits->bits = (uint8_t *) realloc(bits->bits, (newAllocated+7) / 8); bits->bitsAllocated = newAllocated; } ASSERT(bits->bitsAllocated >= bits->bitCount); ASSERT(bits->bitsAllocated >= newCount); } /*********************************************************************** * layout_bitmap_slide * Slide the end of a layout bitmap farther from the start. * Slides bits [oldPos, bits.bitCount) to [newPos, bits.bitCount+newPos-oldPos) * Bits [oldPos, newPos) are zero-filled. * The bitmap is expanded and bitCount updated if necessary. * newPos >= oldPos. **********************************************************************/ void layout_bitmap_slide(layout_bitmap *bits, size_t oldPos, size_t newPos) { size_t shift; size_t count; if (oldPos == newPos) return; if (oldPos > newPos) _objc_fatal("layout bitmap sliding backwards"); shift = newPos - oldPos; count = bits->bitCount - oldPos; layout_bitmap_grow(bits, bits->bitCount + shift); move_bits(*bits, oldPos, newPos, count); // slide clear_bits(*bits, oldPos, shift); // zero-fill } /*********************************************************************** * layout_bitmap_slide_anywhere * Slide the end of a layout bitmap relative to the start. * Like layout_bitmap_slide, but can slide backwards too. * The end of the bitmap is truncated. **********************************************************************/ void layout_bitmap_slide_anywhere(layout_bitmap *bits, size_t oldPos, size_t newPos) { size_t shift; size_t count; if (oldPos == newPos) return; if (oldPos < newPos) { layout_bitmap_slide(bits, oldPos, newPos); return; } shift = oldPos - newPos; count = bits->bitCount - oldPos; move_bits(*bits, oldPos, newPos, count); // slide bits->bitCount -= shift; } /*********************************************************************** * layout_bitmap_splat * Pastes the contents of bitmap src to the start of bitmap dst. * dst bits between the end of src and oldSrcInstanceSize are zeroed. * dst must be at least as long as src. * Returns YES if any of dst's bits were changed. **********************************************************************/ bool layout_bitmap_splat(layout_bitmap dst, layout_bitmap src, size_t oldSrcInstanceSize) { bool changed; size_t oldSrcBitCount; size_t bit; if (dst.bitCount < src.bitCount) _objc_fatal("layout bitmap too short"); changed = NO; oldSrcBitCount = oldSrcInstanceSize / sizeof(id); // fixme optimize for byte/word at a time for (bit = 0; bit < oldSrcBitCount; bit++) { int dstset = dst.bits[bit/8] & (1 << (bit % 8)); int srcset = (bit < src.bitCount) ? src.bits[bit/8] & (1 << (bit % 8)) : 0; if (dstset != srcset) { changed = YES; if (srcset) { dst.bits[bit/8] |= 1 << (bit % 8); } else { dst.bits[bit/8] &= ~(1 << (bit % 8)); } } } return changed; } /*********************************************************************** * layout_bitmap_or * Set dst=dst|src. * dst must be at least as long as src. * Returns YES if any of dst's bits were changed. **********************************************************************/ bool layout_bitmap_or(layout_bitmap dst, layout_bitmap src, const char *msg) { bool changed = NO; size_t bit; if (dst.bitCount < src.bitCount) { _objc_fatal("layout_bitmap_or: layout bitmap too short%s%s", msg ? ": " : "", msg ? msg : ""); } // fixme optimize for byte/word at a time for (bit = 0; bit < src.bitCount; bit++) { int dstset = dst.bits[bit/8] & (1 << (bit % 8)); int srcset = src.bits[bit/8] & (1 << (bit % 8)); if (srcset && !dstset) { changed = YES; dst.bits[bit/8] |= 1 << (bit % 8); } } return changed; } /*********************************************************************** * layout_bitmap_clear * Set dst=dst&~src. * dst must be at least as long as src. * Returns YES if any of dst's bits were changed. **********************************************************************/ bool layout_bitmap_clear(layout_bitmap dst, layout_bitmap src, const char *msg) { bool changed = NO; size_t bit; if (dst.bitCount < src.bitCount) { _objc_fatal("layout_bitmap_clear: layout bitmap too short%s%s", msg ? ": " : "", msg ? msg : ""); } // fixme optimize for byte/word at a time for (bit = 0; bit < src.bitCount; bit++) { int dstset = dst.bits[bit/8] & (1 << (bit % 8)); int srcset = src.bits[bit/8] & (1 << (bit % 8)); if (srcset && dstset) { changed = YES; dst.bits[bit/8] &= ~(1 << (bit % 8)); } } return changed; } void layout_bitmap_print(layout_bitmap bits) { size_t i; printf("%zu: ", bits.bitCount); for (i = 0; i < bits.bitCount; i++) { int set = bits.bits[i/8] & (1 << (i % 8)); printf("%c", set ? '#' : '.'); } printf("\n"); } #if 0 // The code below may be useful when interpreting ivar types more precisely. /********************************************************************** * mark_offset_for_layout * * Marks the appropriate bit in the bits array cooresponding to a the * offset of a reference. If we are scanning a nested pointer structure * then the bits array will be NULL then this function does nothing. * **********************************************************************/ static void mark_offset_for_layout(long offset, long bits_size, unsigned char *bits) { // references are ignored if bits is NULL if (bits) { long slot = offset / sizeof(long); // determine byte index using (offset / 8 bits per byte) long i_byte = slot >> 3; // if the byte index is valid if (i_byte < bits_size) { // set the (offset / 8 bits per byte)th bit bits[i_byte] |= 1 << (slot & 7); } else { // offset not within instance size _objc_inform ("layout - offset exceeds instance size"); } } } /********************************************************************** * skip_ivar_type_name * * Skip over the name of a field/class in an ivar type string. Names * are in the form of a double-quoted string. Returns the remaining * string. * **********************************************************************/ static char *skip_ivar_type_name(char *type) { // current character char ch; // if there is an open quote if (*type == '\"') { // skip quote type++; // while no closing quote while ((ch = *type) != '\"') { // if end of string return end of string if (!ch) return type; // skip character type++; } // skip closing quote type++; } // return remaining string return type; } /********************************************************************** * skip_ivar_struct_name * * Skip over the name of a struct in an ivar type string. Names * may be followed by an equals sign. Returns the remaining string. * **********************************************************************/ static char *skip_ivar_struct_name(char *type) { // get first character char ch = *type; if (ch == _C_UNDEF) { // skip undefined name type++; } else if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '_') { // if alphabetic // scan alphanumerics do { // next character ch = *++type; } while ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '_' || (ch >= '0' && ch <= '9')); } else { // no struct name present return type; } // skip equals sign if (*type == '=') type++; return type; } /********************************************************************** * scan_basic_ivar_type * * Determines the size and alignment of a basic ivar type. If the basic * type is a possible reference to another garbage collected type the * is_reference is set to true (false otherwise.) Returns the remaining * string. * **********************************************************************/ static char *scan_ivar_type_for_layout(char *type, long offset, long bits_size, unsigned char *bits, long *next_offset); static char *scan_basic_ivar_type(char *type, long *size, long *alignment, bool *is_reference) { // assume it is a non-reference type *is_reference = NO; // get the first character (advancing string) const char *full_type = type; char ch = *type++; // GCC 4 uses for const type*. if (ch == _C_CONST) ch = *type++; // act on first character switch (ch) { case _C_ID: { // ID type // skip over optional class name type = skip_ivar_type_name(type); // size and alignment of an id type *size = sizeof(id); *alignment = __alignof(id); // is a reference type *is_reference = YES; break; } case _C_PTR: { // C pointer type // skip underlying type long ignored_offset; type = scan_ivar_type_for_layout(type, 0, 0, NULL, &ignored_offset); // size and alignment of a generic pointer type *size = sizeof(void *); *alignment = __alignof(void *); // is a reference type *is_reference = YES; break; } case _C_CHARPTR: { // C string // size and alignment of a char pointer type *size = sizeof(char *); *alignment = __alignof(char *); // is a reference type *is_reference = YES; break; } case _C_CLASS: case _C_SEL: { // classes and selectors are ignored for now *size = sizeof(void *); *alignment = __alignof(void *); break; } case _C_CHR: case _C_UCHR: { // char and unsigned char *size = sizeof(char); *alignment = __alignof(char); break; } case _C_SHT: case _C_USHT: { // short and unsigned short *size = sizeof(short); *alignment = __alignof(short); break; } case _C_ATOM: case _C_INT: case _C_UINT: { // int and unsigned int *size = sizeof(int); *alignment = __alignof(int); break; } case _C_LNG: case _C_ULNG: { // long and unsigned long *size = sizeof(long); *alignment = __alignof(long); break; } case _C_LNG_LNG: case _C_ULNG_LNG: { // long long and unsigned long long *size = sizeof(long long); *alignment = __alignof(long long); break; } case _C_VECTOR: { // vector *size = 16; *alignment = 16; break; } case _C_FLT: { // float *size = sizeof(float); *alignment = __alignof(float); break; } case _C_DBL: { // double *size = sizeof(double); *alignment = __alignof(double); break; } case _C_BFLD: { // bit field // get number of bits in bit field (advance type string) long lng = strtol(type, &type, 10); // while next type is a bit field while (*type == _C_BFLD) { // skip over _C_BFLD type++; // get next bit field length long next_lng = strtol(type, &type, 10); // if spans next word then align to next word if ((lng & ~31) != ((lng + next_lng) & ~31)) lng = (lng + 31) & ~31; // increment running length lng += next_lng; // skip over potential field name type = skip_ivar_type_name(type); } // determine number of bytes bits represent *size = (lng + 7) / 8; // byte alignment *alignment = __alignof(char); break; } case _C_BOOL: { // double *size = sizeof(BOOL); *alignment = __alignof(BOOL); break; } case _C_VOID: { // skip void types *size = 0; *alignment = __alignof(char); break; } case _C_UNDEF: { *size = 0; *alignment = __alignof(char); break; } default: { // unhandled type _objc_fatal("unrecognized character \'%c\' in ivar type: \"%s\"", ch, full_type); } } return type; } /********************************************************************** * scan_ivar_type_for_layout * * Scan an ivar type string looking for references. The offset indicates * where the ivar begins. bits is a byte array of size bits_size used to * contain the references bit map. next_offset is the offset beyond the * ivar. Returns the remaining string. * **********************************************************************/ static char *scan_ivar_type_for_layout(char *type, long offset, long bits_size, unsigned char *bits, long *next_offset) { long size; // size of a basic type long alignment; // alignment of the basic type bool is_reference; // true if the type indicates a reference to a garbage collected object // get the first character char ch = *type; // GCC 4 uses for const type*. if (ch == _C_CONST) ch = *++type; // act on first character switch (ch) { case _C_ARY_B: { // array type // get the array length long lng = strtol(type + 1, &type, 10); // next type will be where to advance the type string once the array is processed char *next_type = type; // repeat the next type x lng if (!lng) { next_type = scan_ivar_type_for_layout(type, 0, 0, NULL, &offset); } else { while (lng--) { // repeatedly scan the same type next_type = scan_ivar_type_for_layout(type, offset, bits_size, bits, &offset); } } // advance the type now type = next_type; // after the end of the array *next_offset = offset; // advance over closing bracket if (*type == _C_ARY_E) type++; else _objc_inform("missing \'%c\' in ivar type.", _C_ARY_E); break; } case _C_UNION_B: { // union type // skip over possible union name type = skip_ivar_struct_name(type + 1); // need to accumulate the maximum element offset long max_offset = 0; // while not closing paren while ((ch = *type) && ch != _C_UNION_E) { // skip over potential field name type = skip_ivar_type_name(type); // scan type long union_offset; type = scan_ivar_type_for_layout(type, offset, bits_size, bits, &union_offset); // adjust the maximum element offset if (max_offset < union_offset) max_offset = union_offset; } // after the largest element *next_offset = max_offset; // advance over closing paren if (ch == _C_UNION_E) { type++; } else { _objc_inform("missing \'%c\' in ivar type", _C_UNION_E); } break; } case _C_STRUCT_B: { // struct type // skip over possible struct name type = skip_ivar_struct_name(type + 1); // while not closing brace while ((ch = *type) && ch != _C_STRUCT_E) { // skip over potential field name type = skip_ivar_type_name(type); // scan type type = scan_ivar_type_for_layout(type, offset, bits_size, bits, &offset); } // after the end of the struct *next_offset = offset; // advance over closing brace if (ch == _C_STRUCT_E) type++; else _objc_inform("missing \'%c\' in ivar type", _C_STRUCT_E); break; } default: { // basic type // scan type type = scan_basic_ivar_type(type, &size, &alignment, &is_reference); // create alignment mask alignment--; // align offset offset = (offset + alignment) & ~alignment; // if is a reference then mark in the bit map if (is_reference) mark_offset_for_layout(offset, bits_size, bits); // after the basic type *next_offset = offset + size; break; } } // return remainder of type string return type; } #endif