//: Core data structures for simulating the SubX VM (subset of an x86 processor), //: either in tests or debug aids. //:: registers //: assume segment registers are hard-coded to 0 //: no floating-point, MMX, etc. yet :(before "End Types") enum { EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI, NUM_INT_REGISTERS, }; union reg { int32_t i; uint32_t u; }; :(before "End Globals") reg Reg[NUM_INT_REGISTERS] = { {0} }; uint32_t EIP = 1; // preserve null pointer :(before "End Reset") bzero(Reg, sizeof(Reg)); EIP = 1; // preserve null pointer :(before "End Help Contents") cerr << " registers\n"; :(before "End Help Texts") put_new(Help, "registers", "SubX currently supports eight 32-bit integer registers. From 0 to 7, they are:\n" " EAX ECX EDX EBX ESP EBP ESI EDI\n" "ESP contains the top of the stack.\n" "\n" "-- 8-bit registers\n" "Some instructions operate on eight *overlapping* 8-bit registers.\n" "From 0 to 7, they are:\n" " AL CL DL BL AH CH DH BH\n" "The 8-bit registers overlap with the 32-bit ones. AL is the lowest signicant byte\n" "of EAX, AH is the second lowest significant byte, and so on.\n" "\n" "For example, if EBX contains 0x11223344, then BL contains 0x44, and BH contains 0x33.\n" "\n" "There is no way to access bytes within ESP, EBP, ESI or EDI.\n" "\n" "For complete details consult the IA-32 software developer's manual, volume 2,\n" "table 2-2, \"32-bit addressing forms with the ModR/M byte\".\n" "It is included in this repository as 'modrm.pdf'.\n" "The register encodings are described in the top row of the table, but you'll need\n" "to spend some time with it.\n" "\n" "-- flag registers\n" "Various instructions (particularly 'compare') modify one or more of four 1-bit\n" "'flag' registers, as a side-effect:\n" "- the sign flag (SF): usually set if an arithmetic result is negative, or\n" " reset if not.\n" "- the zero flag (ZF): usually set if a result is zero, or reset if not.\n" "- the carry flag (CF): usually set if an arithmetic result overflows by just one bit.\n" " Useful for operating on unsigned numbers.\n" "- the overflow flag (OF): usually set if an arithmetic result overflows by more\n" " than one bit. Useful for operating on signed numbers.\n" "The flag bits are read by conditional jumps.\n" "\n" "For complete details on how different instructions update the flags, consult the IA-32\n" "manual (volume 2). There's various versions of it online, such as https://c9x.me/x86,\n" "though of course you'll need to be careful to ignore instructions and flag registers\n" "that SubX doesn't support.\n" "\n" "It isn't simple, but if this is the processor you have running on your computer.\n" "Might as well get good at it.\n" ); :(before "End Globals") // the subset of x86 flag registers we care about bool SF = false; // sign flag bool ZF = false; // zero flag bool CF = false; // carry flag bool OF = false; // overflow flag :(before "End Reset") SF = ZF = CF = OF = false; //:: simulated RAM :(before "End Types") const uint32_t SEGMENT_ALIGNMENT = 0x1000000; // 16MB inline uint32_t align_upwards(uint32_t x, uint32_t align) { return (x+align-1) & -(align); } // Like in real-world Linux, we'll allocate RAM for our programs in disjoint // slabs called VMAs or Virtual Memory Areas. struct vma { uint32_t start; // inclusive uint32_t end; // exclusive vector _data; vma(uint32_t s, uint32_t e) :start(s), end(e) {} vma(uint32_t s) :start(s), end(align_upwards(s+1, SEGMENT_ALIGNMENT)) {} bool match(uint32_t a) { return a >= start && a < end; } bool match32(uint32_t a) { return a >= start && a+4 <= end; } uint8_t& data(uint32_t a) { assert(match(a)); uint32_t result_index = a-start; if (_data.size() <= result_index) { const int align = 0x1000; uint32_t result_size = result_index + 1; // size needed for result_index to be valid uint32_t new_size = align_upwards(result_size, align); // grow at least 2x to maintain some amortized complexity guarantees if (new_size < _data.size() * 2) new_size = _data.size() * 2; // never grow past the stated limit if (new_size > end-start) new_size = end-start; _data.resize(new_size); } return _data.at(result_index); } void grow_until(uint32_t new_end_address) { if (new_end_address < end) return; // Ugly: vma knows about the global Memory list of vmas void sanity_check(uint32_t start, uint32_t end); sanity_check(start, new_end_address); end = new_end_address; } // End vma Methods }; :(code) void sanity_check(uint32_t start, uint32_t end) { bool dup_found = false; for (int i = 0; i < SIZE(Mem); ++i) { const vma& curr = Mem.at(i); if (curr.start == start) { assert(!dup_found); dup_found = true; } else if (curr.start > start) { assert(curr.start > end); } else if (curr.start < start) { assert(curr.end < start); } } } :(before "End Globals") // RAM is made of VMAs. vector Mem; :(code) :(before "End Globals") uint32_t End_of_program = 0; // when the program executes past this address in tests we'll stop the test // The stack grows downward. Can't increase its size for now. :(before "End Reset") Mem.clear(); End_of_program = 0; :(code) // These helpers depend on Mem being laid out contiguously (so you can't use a // map, etc.) and on the host also being little-endian. inline uint8_t read_mem_u8(uint32_t addr) { uint8_t* handle = mem_addr_u8(addr); // error messages get printed here return handle ? *handle : 0; } inline int8_t read_mem_i8(uint32_t addr) { return static_cast(read_mem_u8(addr)); } inline uint32_t read_mem_u32(uint32_t addr) { uint32_t* handle = mem_addr_u32(addr); // error messages get printed here return handle ? *handle : 0; } inline int32_t read_mem_i32(uint32_t addr) { return static_cast(read_mem_u32(addr)); } inline uint8_t* mem_addr_u8(uint32_t addr) { uint8_t* result = NULL; for (int i = 0; i < SIZE(Mem); ++i) { if (Mem.at(i).match(addr)) { if (result) raise << "address 0x" << HEXWORD << addr << " is in two segments\n" << end(); result = &Mem.at(i).data(addr); } } if (result == NULL) { if (Trace_file) Trace_file.flush(); raise << "Tried to access uninitialized memory at address 0x" << HEXWORD << addr << '\n' << end(); exit(1); } return result; } inline int8_t* mem_addr_i8(uint32_t addr) { return reinterpret_cast(mem_addr_u8(addr)); } inline uint32_t* mem_addr_u32(uint32_t addr) { uint32_t* result = NULL; for (int i = 0; i < SIZE(Mem); ++i) { if (Mem.at(i).match32(addr)) { if (result) raise << "address 0x" << HEXWORD << addr << " is in two segments\n" << end(); result = reinterpret_cast(&Mem.at(i).data(addr)); } } if (result == NULL) { if (Trace_file) Trace_file.flush(); raise << "Tried to access uninitialized memory at address 0x" << HEXWORD << addr << '\n' << end(); raise << "The entire 4-byte word should be initialized and lie in a single segment.\n" << end(); exit(1); } return result; } inline int32_t* mem_addr_i32(uint32_t addr) { return reinterpret_cast(mem_addr_u32(addr)); } // helper for some syscalls. But read-only. inline const char* mem_addr_kernel_string(uint32_t addr) { return reinterpret_cast(mem_addr_u8(addr)); } inline string mem_addr_string(uint32_t addr, uint32_t size) { ostringstream out; for (size_t i = 0; i < size; ++i) out << read_mem_u8(addr+i); return out.str(); } inline void write_mem_u8(uint32_t addr, uint8_t val) { uint8_t* handle = mem_addr_u8(addr); if (handle != NULL) *handle = val; } inline void write_mem_i8(uint32_t addr, int8_t val) { int8_t* handle = mem_addr_i8(addr); if (handle != NULL) *handle = val; } inline void write_mem_u32(uint32_t addr, uint32_t val) { uint32_t* handle = mem_addr_u32(addr); if (handle != NULL) *handle = val; } inline void write_mem_i32(uint32_t addr, int32_t val) { int32_t* handle = mem_addr_i32(addr); if (handle != NULL) *handle = val; } inline bool already_allocated(uint32_t addr) { bool result = false; for (int i = 0; i < SIZE(Mem); ++i) { if (Mem.at(i).match(addr)) { if (result) raise << "address 0x" << HEXWORD << addr << " is in two segments\n" << end(); result = true; } } return result; } //:: core interpreter loop :(code) // skeleton of how x86 instructions are decoded void run_one_instruction() { uint8_t op=0, op2=0, op3=0; // Run One Instruction if (Trace_file) { dump_registers(); // End Dump Info for Instruction } uint32_t inst_start_address = EIP; op = next(); trace(Callstack_depth+1, "run") << "0x" << HEXWORD << inst_start_address << " opcode: " << HEXBYTE << NUM(op) << end(); switch (op) { case 0xf4: // hlt EIP = End_of_program; break; // End Single-Byte Opcodes case 0x0f: switch(op2 = next()) { // End Two-Byte Opcodes Starting With 0f default: cerr << "unrecognized second opcode after 0f: " << HEXBYTE << NUM(op2) << '\n'; exit(1); } break; case 0xf2: switch(op2 = next()) { // End Two-Byte Opcodes Starting With f2 case 0x0f: switch(op3 = next()) { // End Three-Byte Opcodes Starting With f2 0f default: cerr << "unrecognized third opcode after f2 0f: " << HEXBYTE << NUM(op3) << '\n'; exit(1); } break; default: cerr << "unrecognized second opcode after f2: " << HEXBYTE << NUM(op2) << '\n'; exit(1); } break; case 0xf3: switch(op2 = next()) { // End Two-Byte Opcodes Starting With f3 case 0x0f: switch(op3 = next()) { // End Three-Byte Opcodes Starting With f3 0f default: cerr << "unrecognized third opcode after f3 0f: " << HEXBYTE << NUM(op3) << '\n'; exit(1); } break; default: cerr << "unrecognized second opcode after f3: " << HEXBYTE << NUM(op2) << '\n'; exit(1); } break; default: cerr << "unrecognized opcode: " << HEXBYTE << NUM(op) << '\n'; exit(1); } } inline uint8_t next() { return read_mem_u8(EIP++); } void dump_registers() { ostringstream out; out << "regs: "; for (int i = 0; i < NUM_INT_REGISTERS; ++i) { if (i > 0) out << " "; out << i << ": " << std::hex << std::setw(8) << std::setfill('_') << Reg[i].u; } out << " -- SF: " << SF << "; ZF: " << ZF << "; CF: " << CF << "; OF: " << OF; trace(Callstack_depth+1, "run") << out.str() << end(); } //: start tracking supported opcodes :(before "End Globals") map Name; map Name_0f; map Name_f3; map Name_f3_0f; :(before "End One-time Setup") init_op_names(); :(code) void init_op_names() { put(Name, "f4", "halt (hlt)"); // End Initialize Op Names } :(before "End Help Special-cases(key)") if (key == "opcodes") { cerr << "Opcodes currently supported by SubX:\n"; for (map::iterator p = Name.begin(); p != Name.end(); ++p) cerr << " " << p->first << ": " << p->second << '\n'; for (map::iterator p = Name_0f.begin(); p != Name_0f.end(); ++p) cerr << " 0f " << p->first << ": " << p->second << '\n'; for (map::iterator p = Name_f3.begin(); p != Name_f3.end(); ++p) cerr << " f3 " << p->first << ": " << p->second << '\n'; for (map::iterator p = Name_f3_0f.begin(); p != Name_f3_0f.end(); ++p) cerr << " f3 0f " << p->first << ": " << p->second << '\n'; cerr << "Run `bootstrap help instructions` for details on words like 'r32' and 'disp8'.\n" "For complete details on these instructions, consult the IA-32 manual (volume 2).\n" >__dict__[attrname] def __call__(self, *_): return Fake() def __clear__(self): self.__dict__.clear() def __iter__(self): return iter(()) class OK(Exception): pass def raise_ok(*_, **