xCode Issue

Would make it more readable with code formatter tool… It is new year, I'll do it for you.

struct rebindings_entry {
    struct rebinding *rebindings;
    size_t rebindings_nel;
    struct rebindings_entry *next;
};

static struct rebindings_entry *_rebindings_head;

static int prepend_rebindings(struct rebindings_entry **rebindings_head,
                              struct rebinding rebindings[],
                              size_t nel) {
    struct rebindings_entry *new_entry = malloc(sizeof(struct rebindings_entry));
    if (!new_entry) {
        return -1;
    }
    new_entry->rebindings = malloc(sizeof(struct rebinding) * nel);
    if (!new_entry->rebindings) {
        free(new_entry);
        return -1;
    }
    memcpy(new_entry->rebindings, rebindings, sizeof(struct rebinding) * nel);
    new_entry->rebindings_nel = nel;
    new_entry->next = *rebindings_head;
    *rebindings_head = new_entry;
    return 0;
}

static void perform_rebinding_with_section(struct rebindings_entry *rebindings,
                                           section_t *section,
                                           intptr_t slide,
                                           nlist_t *symtab,
                                           char *strtab,
                                           uint32_t *indirect_symtab) {
    uint32_t *indirect_symbol_indices = indirect_symtab + section->reserved1;
    void **indirect_symbol_bindings = (void **)((uintptr_t)slide + section->addr);
    for (uint i = 0; i < section->size / sizeof(void *); i++) {
        uint32_t symtab_index = indirect_symbol_indices[i];
        if (symtab_index == INDIRECT_SYMBOL_ABS || symtab_index == INDIRECT_SYMBOL_LOCAL ||
            symtab_index == (INDIRECT_SYMBOL_LOCAL   | INDIRECT_SYMBOL_ABS)) {
            continue;
        }
        uint32_t strtab_offset = symtab[symtab_index].n_un.n_strx;
        char *symbol_name = strtab + strtab_offset;
        struct rebindings_entry *cur = rebindings;
        while (cur) {
            for (uint j = 0; j < cur->rebindings_nel; j++) {
                if (strlen(symbol_name) > 1 &&
                    strcmp(&symbol_name[1], cur->rebindings[j].name) == 0) {
                    indirect_symbol_bindings[i] = cur->rebindings[j].replacement; // **Thread 1: EXC_BAD_ACCESS (code=2, address=0x7fff8647d5c8)**
                    goto symbol_loop;
                }
            }
            cur = cur->next;
        }
    symbol_loop:;
    }
}

static void rebind_symbols_for_image(struct rebindings_entry *rebindings,
                                     const struct mach_header *header,
                                     intptr_t slide) {
    Dl_info info;
    if (dladdr(header, &info) == 0) {
        return;
    }
    
    segment_command_t *cur_seg_cmd;
    segment_command_t *linkedit_segment = NULL;
    struct symtab_command* symtab_cmd = NULL;
    struct dysymtab_command* dysymtab_cmd = NULL;
    
    uintptr_t cur = (uintptr_t)header + sizeof(mach_header_t);
    for (uint i = 0; i < header->ncmds; i++, cur += cur_seg_cmd->cmdsize) {
        cur_seg_cmd = (segment_command_t *)cur;
        if (cur_seg_cmd->cmd == LC_SEGMENT_ARCH_DEPENDENT) {
            if (strcmp(cur_seg_cmd->segname, SEG_LINKEDIT) == 0) {
                linkedit_segment = cur_seg_cmd;
            }
        } else if (cur_seg_cmd->cmd == LC_SYMTAB) {
            symtab_cmd = (struct symtab_command*)cur_seg_cmd;
        } else if (cur_seg_cmd->cmd == LC_DYSYMTAB) {
            dysymtab_cmd = (struct dysymtab_command*)cur_seg_cmd;
        }
    }
    
    if (!symtab_cmd || !dysymtab_cmd || !linkedit_segment ||
        !dysymtab_cmd->nindirectsyms) {
        return;
    }
    
    // Find base symbol/string table addresses
    uintptr_t linkedit_base = (uintptr_t)slide + linkedit_segment->vmaddr - linkedit_segment->fileoff;
    nlist_t *symtab = (nlist_t *)(linkedit_base + symtab_cmd->symoff);
    char *strtab = (char *)(linkedit_base + symtab_cmd->stroff);
    
    // Get indirect symbol table (array of uint32_t indices into symbol table)
    uint32_t *indirect_symtab = (uint32_t *)(linkedit_base + dysymtab_cmd->indirectsymoff);
    
    cur = (uintptr_t)header + sizeof(mach_header_t);
    for (uint i = 0; i < header->ncmds; i++, cur += cur_seg_cmd->cmdsize) {
        cur_seg_cmd = (segment_command_t *)cur;
        if (cur_seg_cmd->cmd == LC_SEGMENT_ARCH_DEPENDENT) {
            if (strcmp(cur_seg_cmd->segname, SEG_DATA) != 0 &&
                strcmp(cur_seg_cmd->segname, SEG_DATA_CONST) != 0) {
                continue;
            }
            for (uint j = 0; j < cur_seg_cmd->nsects; j++) {
                section_t *sect =
                (section_t *)(cur + sizeof(segment_command_t)) + j;
                if ((sect->flags & SECTION_TYPE) == S_LAZY_SYMBOL_POINTERS) {
                    perform_rebinding_with_section(rebindings, sect, slide, symtab, strtab, indirect_symtab);
                }
                if ((sect->flags & SECTION_TYPE) == S_NON_LAZY_SYMBOL_POINTERS) {
                    perform_rebinding_with_section(rebindings, sect, slide, symtab, strtab, indirect_symtab);
                }
            }
        }
    }
}

static void _rebind_symbols_for_image(const struct mach_header *header,
                                      intptr_t slide) {
    rebind_symbols_for_image(_rebindings_head, header, slide);
}
int rebind_symbols_image(void *header,
                         intptr_t slide,
                         struct rebinding rebindings[],
                         size_t rebindings_nel) {
    struct rebindings_entry *rebindings_head = NULL;
    int retval = prepend_rebindings(&rebindings_head, rebindings, rebindings_nel);
    rebind_symbols_for_image(rebindings_head, header, slide);
    free(rebindings_head);
    return retval;
}

int rebind_symbols(struct rebinding rebindings[], size_t rebindings_nel) {
    int retval = prepend_rebindings(&_rebindings_head, rebindings, rebindings_nel);
    if (retval < 0) {
        return retval;
    }
    // If this was the first call, register callback for image additions (which is also invoked for
    // existing images, otherwise, just run on existing images
    if (!_rebindings_head->next) {
        _dyld_register_func_for_add_image(_rebind_symbols_for_image);
    } else {
        uint32_t c = _dyld_image_count();
        for (uint32_t i = 0; i < c; i++) {
            _rebind_symbols_for_image(_dyld_get_image_header(i), _dyld_get_image_vmaddr_slide(i));
        }
    }
    return retval;
}

Thanks for asking Claude. Just hard to highlight it. We are getting this Thread 1: EXC_BAD_ACCESS (code=2, address=0x7fff8647d5c8) with this section of the full code:

 if (strlen(symbol_name) > 1 &&

                    strcmp(&symbol_name[1], cur->rebindings[j].name) == 0) {

                    indirect_symbol_bindings[i] = cur->rebindings[j].replacement; // Thread 1: EXC_BAD_ACCESS (code=2, address=0x7fff8647d5c8)

                    goto symbol_loop;

Claude, I answered below, but see your comment here. Which code formatter tool do you suggest? Isn't your answer below the exact same code that I had posted above? I am still learning here!

This usually means you have an issue with thread safety, array bounds check error or a reference no longer exists. I will begin by performing NULL & array boundary checks on each array instance before accessing the subscripts.