Mercurial > hg > graal-jvmci-8
view src/share/vm/runtime/relocator.cpp @ 6982:e4f764ddb06a
7122219: Passed StringTableSize value not verified
Summary: Check that the values specified for -XX:StringTableSize are within a certain range.
Reviewed-by: dholmes, coleenp
author | hseigel |
---|---|
date | Mon, 12 Nov 2012 15:58:11 -0500 |
parents | da91efe96a93 |
children | 63a4eb8bcd23 |
line wrap: on
line source
/* * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "precompiled.hpp" #include "classfile/stackMapTableFormat.hpp" #include "interpreter/bytecodes.hpp" #include "memory/metadataFactory.hpp" #include "memory/oopFactory.hpp" #include "memory/universe.inline.hpp" #include "oops/oop.inline.hpp" #include "runtime/handles.inline.hpp" #include "runtime/relocator.hpp" #define MAX_METHOD_LENGTH 65535 #define MAX_SHORT ((1 << 15) - 1) #define MIN_SHORT (- (1 << 15)) // Encapsulates a code change request. There are 3 types. // General instruction, jump instruction, and table/lookup switches // class ChangeItem : public ResourceObj { int _bci; public: ChangeItem(int bci) { _bci = bci; } virtual bool handle_code_change(Relocator *r) = 0; // type info virtual bool is_widen() { return false; } virtual bool is_jump_widen() { return false; } virtual bool is_switch_pad() { return false; } // accessors int bci() { return _bci; } void relocate(int break_bci, int delta) { if (_bci > break_bci) { _bci += delta; } } virtual bool adjust(int bci, int delta) { return false; } // debug virtual void print() = 0; }; class ChangeWiden : public ChangeItem { int _new_ilen; // New length of instruction at bci u_char* _inst_buffer; // New bytecodes public: ChangeWiden(int bci, int new_ilen, u_char* inst_buffer) : ChangeItem(bci) { _new_ilen = new_ilen; _inst_buffer = inst_buffer; } // Callback to do instruction bool handle_code_change(Relocator *r) { return r->handle_widen(bci(), _new_ilen, _inst_buffer); }; bool is_widen() { return true; } void print() { tty->print_cr("ChangeWiden. bci: %d New_ilen: %d", bci(), _new_ilen); } }; class ChangeJumpWiden : public ChangeItem { int _delta; // New length of instruction at bci public: ChangeJumpWiden(int bci, int delta) : ChangeItem(bci) { _delta = delta; } // Callback to do instruction bool handle_code_change(Relocator *r) { return r->handle_jump_widen(bci(), _delta); }; bool is_jump_widen() { return true; } // If the bci matches, adjust the delta in the change jump request. bool adjust(int jump_bci, int delta) { if (bci() == jump_bci) { if (_delta > 0) _delta += delta; else _delta -= delta; return true; } return false; } void print() { tty->print_cr("ChangeJumpWiden. bci: %d Delta: %d", bci(), _delta); } }; class ChangeSwitchPad : public ChangeItem { int _padding; bool _is_lookup_switch; public: ChangeSwitchPad(int bci, int padding, bool is_lookup_switch) : ChangeItem(bci) { _padding = padding; _is_lookup_switch = is_lookup_switch; } // Callback to do instruction bool handle_code_change(Relocator *r) { return r->handle_switch_pad(bci(), _padding, _is_lookup_switch); }; bool is_switch_pad() { return true; } int padding() { return _padding; } bool is_lookup_switch() { return _is_lookup_switch; } void print() { tty->print_cr("ChangeSwitchPad. bci: %d Padding: %d IsLookupSwitch: %d", bci(), _padding, _is_lookup_switch); } }; //----------------------------------------------------------------------------------------------------------- // Relocator code Relocator::Relocator(methodHandle m, RelocatorListener* listener) { set_method(m); set_code_length(method()->code_size()); set_code_array(NULL); // Allocate code array and copy bytecodes if (!expand_code_array(0)) { // Should have at least MAX_METHOD_LENGTH available or the verifier // would have failed. ShouldNotReachHere(); } set_compressed_line_number_table(NULL); set_compressed_line_number_table_size(0); _listener = listener; } // size is the new size of the instruction at bci. Hence, if size is less than the current // instruction sice, we will shrink the code. methodHandle Relocator::insert_space_at(int bci, int size, u_char inst_buffer[], TRAPS) { _changes = new GrowableArray<ChangeItem*> (10); _changes->push(new ChangeWiden(bci, size, inst_buffer)); if (TraceRelocator) { tty->print_cr("Space at: %d Size: %d", bci, size); _method->print(); _method->print_codes(); tty->print_cr("-------------------------------------------------"); } if (!handle_code_changes()) return methodHandle(); // Construct the new method methodHandle new_method = Method::clone_with_new_data(method(), code_array(), code_length(), compressed_line_number_table(), compressed_line_number_table_size(), CHECK_(methodHandle())); // Deallocate the old Method* from metadata ClassLoaderData* loader_data = method()->method_holder()->class_loader_data(); loader_data->add_to_deallocate_list(method()()); set_method(new_method); if (TraceRelocator) { tty->print_cr("-------------------------------------------------"); tty->print_cr("new method"); _method->print_codes(); } return new_method; } bool Relocator::handle_code_changes() { assert(_changes != NULL, "changes vector must be initialized"); while (!_changes->is_empty()) { // Inv: everything is aligned. ChangeItem* ci = _changes->first(); if (TraceRelocator) { ci->print(); } // Execute operation if (!ci->handle_code_change(this)) return false; // Shuffel items up for (int index = 1; index < _changes->length(); index++) { _changes->at_put(index-1, _changes->at(index)); } _changes->pop(); } return true; } bool Relocator::is_opcode_lookupswitch(Bytecodes::Code bc) { switch (bc) { case Bytecodes::_tableswitch: return false; case Bytecodes::_lookupswitch: // not rewritten on ia64 case Bytecodes::_fast_linearswitch: // rewritten _lookupswitch case Bytecodes::_fast_binaryswitch: return true; // rewritten _lookupswitch default: ShouldNotReachHere(); } return true; // dummy } // We need a special instruction size method, since lookupswitches and tableswitches might not be // properly alligned during relocation int Relocator::rc_instr_len(int bci) { Bytecodes::Code bc= code_at(bci); switch (bc) { // In the case of switch instructions, see if we have the original // padding recorded. case Bytecodes::_tableswitch: case Bytecodes::_lookupswitch: case Bytecodes::_fast_linearswitch: case Bytecodes::_fast_binaryswitch: { int pad = get_orig_switch_pad(bci, is_opcode_lookupswitch(bc)); if (pad == -1) { return instruction_length_at(bci); } // Otherwise, depends on the switch type. switch (bc) { case Bytecodes::_tableswitch: { int lo = int_at(bci + 1 + pad + 4 * 1); int hi = int_at(bci + 1 + pad + 4 * 2); int n = hi - lo + 1; return 1 + pad + 4*(3 + n); } case Bytecodes::_lookupswitch: case Bytecodes::_fast_linearswitch: case Bytecodes::_fast_binaryswitch: { int npairs = int_at(bci + 1 + pad + 4 * 1); return 1 + pad + 4*(2 + 2*npairs); } default: ShouldNotReachHere(); } } } return instruction_length_at(bci); } // If a change item is recorded for "pc", with type "ct", returns the // associated padding, else -1. int Relocator::get_orig_switch_pad(int bci, bool is_lookup_switch) { for (int k = 0; k < _changes->length(); k++) { ChangeItem* ci = _changes->at(k); if (ci->is_switch_pad()) { ChangeSwitchPad* csp = (ChangeSwitchPad*)ci; if (csp->is_lookup_switch() == is_lookup_switch && csp->bci() == bci) { return csp->padding(); } } } return -1; } // Push a ChangeJumpWiden if it doesn't already exist on the work queue, // otherwise adjust the item already there by delta. The calculation for // new_delta is wrong for this because it uses the offset stored in the // code stream itself which wasn't fixed when item was pushed on the work queue. void Relocator::push_jump_widen(int bci, int delta, int new_delta) { for (int j = 0; j < _changes->length(); j++) { ChangeItem* ci = _changes->at(j); if (ci->adjust(bci, delta)) return; } _changes->push(new ChangeJumpWiden(bci, new_delta)); } // The current instruction of "c" is a jump; one of its offset starts // at "offset" and is a short if "isShort" is "TRUE", // and an integer otherwise. If the jump crosses "breakPC", change // the span of the jump by "delta". void Relocator::change_jump(int bci, int offset, bool is_short, int break_bci, int delta) { int bci_delta = (is_short) ? short_at(offset) : int_at(offset); int targ = bci + bci_delta; if ((bci <= break_bci && targ > break_bci) || (bci > break_bci && targ <= break_bci)) { int new_delta; if (bci_delta > 0) new_delta = bci_delta + delta; else new_delta = bci_delta - delta; if (is_short && ((new_delta > MAX_SHORT) || new_delta < MIN_SHORT)) { push_jump_widen(bci, delta, new_delta); } else if (is_short) { short_at_put(offset, new_delta); } else { int_at_put(offset, new_delta); } } } // Changes all jumps crossing "break_bci" by "delta". May enqueue things // on "rc->changes" void Relocator::change_jumps(int break_bci, int delta) { int bci = 0; Bytecodes::Code bc; // Now, adjust any affected instructions. while (bci < code_length()) { switch (bc= code_at(bci)) { case Bytecodes::_ifeq: case Bytecodes::_ifne: case Bytecodes::_iflt: case Bytecodes::_ifge: case Bytecodes::_ifgt: case Bytecodes::_ifle: case Bytecodes::_if_icmpeq: case Bytecodes::_if_icmpne: case Bytecodes::_if_icmplt: case Bytecodes::_if_icmpge: case Bytecodes::_if_icmpgt: case Bytecodes::_if_icmple: case Bytecodes::_if_acmpeq: case Bytecodes::_if_acmpne: case Bytecodes::_ifnull: case Bytecodes::_ifnonnull: case Bytecodes::_goto: case Bytecodes::_jsr: change_jump(bci, bci+1, true, break_bci, delta); break; case Bytecodes::_goto_w: case Bytecodes::_jsr_w: change_jump(bci, bci+1, false, break_bci, delta); break; case Bytecodes::_tableswitch: case Bytecodes::_lookupswitch: case Bytecodes::_fast_linearswitch: case Bytecodes::_fast_binaryswitch: { int recPad = get_orig_switch_pad(bci, (bc != Bytecodes::_tableswitch)); int oldPad = (recPad != -1) ? recPad : align(bci+1) - (bci+1); if (bci > break_bci) { int new_bci = bci + delta; int newPad = align(new_bci+1) - (new_bci+1); // Do we need to check the padding? if (newPad != oldPad) { if (recPad == -1) { _changes->push(new ChangeSwitchPad(bci, oldPad, (bc != Bytecodes::_tableswitch))); } } } // Then the rest, which depend on the kind of switch. switch (bc) { case Bytecodes::_tableswitch: { change_jump(bci, bci +1 + oldPad, false, break_bci, delta); // We cannot use the Bytecode_tableswitch abstraction, since the padding might not be correct. int lo = int_at(bci + 1 + oldPad + 4 * 1); int hi = int_at(bci + 1 + oldPad + 4 * 2); int n = hi - lo + 1; for (int k = 0; k < n; k++) { change_jump(bci, bci +1 + oldPad + 4*(k+3), false, break_bci, delta); } // Special next-bci calculation here... bci += 1 + oldPad + (n+3)*4; continue; } case Bytecodes::_lookupswitch: case Bytecodes::_fast_linearswitch: case Bytecodes::_fast_binaryswitch: { change_jump(bci, bci +1 + oldPad, false, break_bci, delta); // We cannot use the Bytecode_lookupswitch abstraction, since the padding might not be correct. int npairs = int_at(bci + 1 + oldPad + 4 * 1); for (int k = 0; k < npairs; k++) { change_jump(bci, bci + 1 + oldPad + 4*(2 + 2*k + 1), false, break_bci, delta); } /* Special next-bci calculation here... */ bci += 1 + oldPad + (2 + (npairs*2))*4; continue; } default: ShouldNotReachHere(); } } default: break; } bci += rc_instr_len(bci); } } // The width of instruction at "pc" is changing by "delta". Adjust the // exception table, if any, of "rc->mb". void Relocator::adjust_exception_table(int bci, int delta) { ExceptionTable table(_method()); for (int index = 0; index < table.length(); index ++) { if (table.start_pc(index) > bci) { table.set_start_pc(index, table.start_pc(index) + delta); table.set_end_pc(index, table.end_pc(index) + delta); } else if (bci < table.end_pc(index)) { table.set_end_pc(index, table.end_pc(index) + delta); } if (table.handler_pc(index) > bci) table.set_handler_pc(index, table.handler_pc(index) + delta); } } // The width of instruction at "bci" is changing by "delta". Adjust the line number table. void Relocator::adjust_line_no_table(int bci, int delta) { if (method()->has_linenumber_table()) { CompressedLineNumberReadStream reader(method()->compressed_linenumber_table()); CompressedLineNumberWriteStream writer(64); // plenty big for most line number tables while (reader.read_pair()) { int adjustment = (reader.bci() > bci) ? delta : 0; writer.write_pair(reader.bci() + adjustment, reader.line()); } writer.write_terminator(); set_compressed_line_number_table(writer.buffer()); set_compressed_line_number_table_size(writer.position()); } } // The width of instruction at "bci" is changing by "delta". Adjust the local variable table. void Relocator::adjust_local_var_table(int bci, int delta) { int localvariable_table_length = method()->localvariable_table_length(); if (localvariable_table_length > 0) { LocalVariableTableElement* table = method()->localvariable_table_start(); for (int i = 0; i < localvariable_table_length; i++) { u2 current_bci = table[i].start_bci; if (current_bci > bci) { table[i].start_bci = current_bci + delta; } else { u2 current_length = table[i].length; if (current_bci + current_length > bci) { table[i].length = current_length + delta; } } } } } // Create a new array, copying the src array but adding a hole at // the specified location static Array<u1>* insert_hole_at(ClassLoaderData* loader_data, size_t where, int hole_sz, Array<u1>* src) { Thread* THREAD = Thread::current(); Array<u1>* dst = MetadataFactory::new_array<u1>(loader_data, src->length() + hole_sz, 0, CHECK_NULL); address src_addr = (address)src->adr_at(0); address dst_addr = (address)dst->adr_at(0); memcpy(dst_addr, src_addr, where); memcpy(dst_addr + where + hole_sz, src_addr + where, src->length() - where); return dst; } // The width of instruction at "bci" is changing by "delta". Adjust the stack // map frames. void Relocator::adjust_stack_map_table(int bci, int delta) { if (method()->has_stackmap_table()) { Array<u1>* data = method()->stackmap_data(); // The data in the array is a classfile representation of the stackmap table stack_map_table* sm_table = stack_map_table::at((address)data->adr_at(0)); int count = sm_table->number_of_entries(); stack_map_frame* frame = sm_table->entries(); int bci_iter = -1; bool offset_adjusted = false; // only need to adjust one offset for (int i = 0; i < count; ++i) { int offset_delta = frame->offset_delta(); bci_iter += offset_delta; if (!offset_adjusted && bci_iter > bci) { int new_offset_delta = offset_delta + delta; if (frame->is_valid_offset(new_offset_delta)) { frame->set_offset_delta(new_offset_delta); } else { assert(frame->is_same_frame() || frame->is_same_locals_1_stack_item_frame(), "Frame must be one of the compressed forms"); // The new delta exceeds the capacity of the 'same_frame' or // 'same_frame_1_stack_item_frame' frame types. We need to // convert these frames to the extended versions, but the extended // version is bigger and requires more room. So we allocate a // new array and copy the data, being sure to leave u2-sized hole // right after the 'frame_type' for the new offset field. // // We can safely ignore the reverse situation as a small delta // can still be used in an extended version of the frame. size_t frame_offset = (address)frame - (address)data->adr_at(0); ClassLoaderData* loader_data = method()->method_holder()->class_loader_data(); Array<u1>* new_data = insert_hole_at(loader_data, frame_offset + 1, 2, data); if (new_data == NULL) { return; // out-of-memory? } // Deallocate old data MetadataFactory::free_array<u1>(loader_data, data); data = new_data; address frame_addr = (address)(data->adr_at(0) + frame_offset); frame = stack_map_frame::at(frame_addr); // Now convert the frames in place if (frame->is_same_frame()) { same_frame_extended::create_at(frame_addr, new_offset_delta); } else { same_locals_1_stack_item_extended::create_at( frame_addr, new_offset_delta, NULL); // the verification_info_type should already be at the right spot } } offset_adjusted = true; // needs to be done only once, since subsequent // values are offsets from the current } // The stack map frame may contain verification types, if so we need to // check and update any Uninitialized type's bci (no matter where it is). int number_of_types = frame->number_of_types(); verification_type_info* types = frame->types(); for (int i = 0; i < number_of_types; ++i) { if (types->is_uninitialized() && types->bci() > bci) { types->set_bci(types->bci() + delta); } types = types->next(); } // Full frame has stack values too full_frame* ff = frame->as_full_frame(); if (ff != NULL) { address eol = (address)types; number_of_types = ff->stack_slots(eol); types = ff->stack(eol); for (int i = 0; i < number_of_types; ++i) { if (types->is_uninitialized() && types->bci() > bci) { types->set_bci(types->bci() + delta); } types = types->next(); } } frame = frame->next(); } method()->set_stackmap_data(data); // in case it has changed } } bool Relocator::expand_code_array(int delta) { int length = MAX2(code_length() + delta, code_length() * (100+code_slop_pct()) / 100); if (length > MAX_METHOD_LENGTH) { if (delta == 0 && code_length() <= MAX_METHOD_LENGTH) { length = MAX_METHOD_LENGTH; } else { return false; } } unsigned char* new_code_array = NEW_RESOURCE_ARRAY(unsigned char, length); if (!new_code_array) return false; // Expanding current array if (code_array() != NULL) { memcpy(new_code_array, code_array(), code_length()); } else { // Initial copy. Copy directly from Method* memcpy(new_code_array, method()->code_base(), code_length()); } set_code_array(new_code_array); set_code_array_length(length); return true; } // The instruction at "bci", whose size is "ilen", is changing size by // "delta". Reallocate, move code, recalculate jumps, and enqueue // change items as necessary. bool Relocator::relocate_code(int bci, int ilen, int delta) { int next_bci = bci + ilen; if (delta > 0 && code_length() + delta > code_array_length()) { // Expand allocated code space, if necessary. if (!expand_code_array(delta)) { return false; } } // We require 4-byte alignment of code arrays. assert(((intptr_t)code_array() & 3) == 0, "check code alignment"); // Change jumps before doing the copying; this routine requires aligned switches. change_jumps(bci, delta); // In case we have shrunken a tableswitch/lookupswitch statement, we store the last // bytes that get overwritten. We have to copy the bytes after the change_jumps method // has been called, since it is likly to update last offset in a tableswitch/lookupswitch if (delta < 0) { assert(delta>=-3, "we cannot overwrite more than 3 bytes"); memcpy(_overwrite, addr_at(bci + ilen + delta), -delta); } memmove(addr_at(next_bci + delta), addr_at(next_bci), code_length() - next_bci); set_code_length(code_length() + delta); // Also adjust exception tables... adjust_exception_table(bci, delta); // Line number tables... adjust_line_no_table(bci, delta); // And local variable table... adjust_local_var_table(bci, delta); // Adjust stack maps adjust_stack_map_table(bci, delta); // Relocate the pending change stack... for (int j = 0; j < _changes->length(); j++) { ChangeItem* ci = _changes->at(j); ci->relocate(bci, delta); } // Notify any listeners about code relocation notify(bci, delta, code_length()); return true; } // relocate a general instruction. Called by ChangeWiden class bool Relocator::handle_widen(int bci, int new_ilen, u_char inst_buffer[]) { int ilen = rc_instr_len(bci); if (!relocate_code(bci, ilen, new_ilen - ilen)) return false; // Insert new bytecode(s) for(int k = 0; k < new_ilen; k++) { code_at_put(bci + k, (Bytecodes::Code)inst_buffer[k]); } return true; } // handle jump_widen instruction. Called be ChangeJumpWiden class bool Relocator::handle_jump_widen(int bci, int delta) { int ilen = rc_instr_len(bci); Bytecodes::Code bc = code_at(bci); switch (bc) { case Bytecodes::_ifeq: case Bytecodes::_ifne: case Bytecodes::_iflt: case Bytecodes::_ifge: case Bytecodes::_ifgt: case Bytecodes::_ifle: case Bytecodes::_if_icmpeq: case Bytecodes::_if_icmpne: case Bytecodes::_if_icmplt: case Bytecodes::_if_icmpge: case Bytecodes::_if_icmpgt: case Bytecodes::_if_icmple: case Bytecodes::_if_acmpeq: case Bytecodes::_if_acmpne: case Bytecodes::_ifnull: case Bytecodes::_ifnonnull: { const int goto_length = Bytecodes::length_for(Bytecodes::_goto); // If 'if' points to the next bytecode after goto, it's already handled. // it shouldn't be. assert (short_at(bci+1) != ilen+goto_length, "if relocation already handled"); assert(ilen == 3, "check length"); // Convert to 0 if <cond> goto 6 // 3 _goto 11 // 6 _goto_w <wide delta offset> // 11 <else code> const int goto_w_length = Bytecodes::length_for(Bytecodes::_goto_w); const int add_bci = goto_length + goto_w_length; if (!relocate_code(bci, 3, /*delta*/add_bci)) return false; // if bytecode points to goto_w instruction short_at_put(bci + 1, ilen + goto_length); int cbci = bci + ilen; // goto around code_at_put(cbci, Bytecodes::_goto); short_at_put(cbci + 1, add_bci); // goto_w <wide delta> cbci = cbci + goto_length; code_at_put(cbci, Bytecodes::_goto_w); if (delta > 0) { delta += 2; // goto_w is 2 bytes more than "if" code } else { delta -= ilen+goto_length; // branch starts at goto_w offset } int_at_put(cbci + 1, delta); break; } case Bytecodes::_goto: case Bytecodes::_jsr: assert(ilen == 3, "check length"); if (!relocate_code(bci, 3, 2)) return false; if (bc == Bytecodes::_goto) code_at_put(bci, Bytecodes::_goto_w); else code_at_put(bci, Bytecodes::_jsr_w); // If it's a forward jump, add 2 for the widening. if (delta > 0) delta += 2; int_at_put(bci + 1, delta); break; default: ShouldNotReachHere(); } return true; } // handle lookup/table switch instructions. Called be ChangeSwitchPad class bool Relocator::handle_switch_pad(int bci, int old_pad, bool is_lookup_switch) { int ilen = rc_instr_len(bci); int new_pad = align(bci+1) - (bci+1); int pad_delta = new_pad - old_pad; if (pad_delta != 0) { int len; if (!is_lookup_switch) { int low = int_at(bci+1+old_pad+4); int high = int_at(bci+1+old_pad+8); len = high-low+1 + 3; // 3 for default, hi, lo. } else { int npairs = int_at(bci+1+old_pad+4); len = npairs*2 + 2; // 2 for default, npairs. } // Because "relocateCode" does a "changeJumps" loop, // which parses instructions to determine their length, // we need to call that before messing with the current // instruction. Since it may also overwrite the current // instruction when moving down, remember the possibly // overwritten part. // Move the code following the instruction... if (!relocate_code(bci, ilen, pad_delta)) return false; if (pad_delta < 0) { // Move the shrunken instruction down. memmove(addr_at(bci + 1 + new_pad), addr_at(bci + 1 + old_pad), len * 4 + pad_delta); memmove(addr_at(bci + 1 + new_pad + len*4 + pad_delta), _overwrite, -pad_delta); } else { assert(pad_delta > 0, "check"); // Move the expanded instruction up. memmove(addr_at(bci +1 + new_pad), addr_at(bci +1 + old_pad), len * 4); memset(addr_at(bci + 1), 0, new_pad); // pad must be 0 } } return true; }