1 //: Core data structures for simulating the SubX VM (subset of an x86 processor),
  2 //: either in tests or debug aids.
  3 
  4 //:: registers
  5 //: assume segment registers are hard-coded to 0
  6 //: no floating-point, MMX, etc. yet
  7 
  8 :(before "End Types")
  9 enum {
 10   EAX,
 11   ECX,
 12   EDX,
 13   EBX,
 14   ESP,
 15   EBP,
 16   ESI,
 17   EDI,
 18   NUM_INT_REGISTERS,
 19 };
 20 union reg {
 21   int32_t i;
 22   uint32_t u;
 23 };
 24 :(before "End Globals")
 25 reg Reg[NUM_INT_REGISTERS] = { {0} };
 26 uint32_t EIP = 1;  // preserve null pointer
 27 :(before "End Reset")
 28 bzero(Reg, sizeof(Reg));
 29 EIP = 1;  // preserve null pointer
 30 
 31 :(before "End Help Contents")
 32 cerr << "  registers\n";
 33 :(before "End Help Texts")
 34 put_new(Help, "registers",
 35   "SubX currently supports eight 32-bit integer registers. From 0 to 7, they are:\n"
 36   "  EAX ECX EDX EBX ESP EBP ESI EDI\n"
 37   "ESP contains the top of the stack.\n"
 38   "\n"
 39   "-- 8-bit registers\n"
 40   "Some instructions operate on eight *overlapping* 8-bit registers.\n"
 41   "From 0 to 7, they are:\n"
 42   "  AL CL DL BL AH CH DH BH\n"
 43   "The 8-bit registers overlap with the 32-bit ones. AL is the lowest signicant byte\n"
 44   "of EAX, AH is the second lowest significant byte, and so on.\n"
 45   "\n"
 46   "For example, if EBX contains 0x11223344, then BL contains 0x44, and BH contains 0x33.\n"
 47   "\n"
 48   "There is no way to access bytes within ESP, EBP, ESI or EDI.\n"
 49   "\n"
 50   "For complete details consult the IA-32 software developer's manual, volume 2,\n"
 51   "table 2-2, \"32-bit addressing forms with the ModR/M byte\".\n"
 52   "It is included in this repository as 'modrm.pdf'.\n"
 53   "The register encodings are described in the top row of the table, but you'll need\n"
 54   "to spend some time with it.\n"
 55   "\n"
 56   "-- flag registers\n"
 57   "Various instructions (particularly 'compare') modify one or more of four 1-bit\n"
 58   "'flag' registers, as a side-effect:\n"
 59   "- the sign flag (SF): usually set if an arithmetic result is negative, or\n"
 60   "  reset if not.\n"
 61   "- the zero flag (ZF): usually set if a result is zero, or reset if not.\n"
 62   "- the carry flag (CF): usually set if an arithmetic result overflows by just one bit.\n"
 63   "  Useful for operating on unsigned numbers.\n"
 64   "- the overflow flag (OF): usually set if an arithmetic result overflows by more\n"
 65   "  than one bit. Useful for operating on signed numbers.\n"
 66   "The flag bits are read by conditional jumps.\n"
 67   "\n"
 68   "For complete details on how different instructions update the flags, consult the IA-32\n"
 69   "manual (volume 2). There's various versions of it online, such as https://c9x.me/x86,\n"
 70   "though of course you'll need to be careful to ignore instructions and flag registers\n"
 71   "that SubX doesn't support.\n"
 72   "\n"
 73   "It isn't simple, but if this is the processor you have running on your computer.\n"
 74   "Might as well get good at it.\n"
 75 );
 76 
 77 :(before "End Globals")
 78 // the subset of x86 flag registers we care about
 79 bool SF = false;  // sign flag
 80 bool ZF = false;  // zero flag
 81 bool CF = false;  // carry flag
 82 bool OF = false;  // overflow flag
 83 :(before "End Reset")
 84 SF = ZF = CF = OF = false;
 85 
 86 //:: simulated RAM
 87 
 88 :(before "End Types")
 89 const uint32_t SEGMENT_ALIGNMENT = 0x1000000;  // 16MB
 90 inline uint32_t align_upwards(uint32_t x, uint32_t align) {
 91   return (x+align-1) & -(align);
 92 }
 93 
 94 // Like in real-world Linux, we'll allocate RAM for our programs in disjoint
 95 // slabs called VMAs or Virtual Memory Areas.
 96 struct vma {
 97   uint32_t start;  // inclusive
 98   uint32_t end;  // exclusive
 99   vector<uint8_t> _data;
100   vma(uint32_t s, uint32_t e) :start(s), end(e) {}
101   vma(uint32_t s) :start(s), end(align_upwards(s+1, SEGMENT_ALIGNMENT)) {}
102   bool match(uint32_t a) {
103     return a >= start && a < end;
104   }
105   bool match32(uint32_t a) {
106     return a >= start && a+4 <= end;
107   }
108   uint8_t& data(uint32_t a) {
109     assert(match(a));
110     uint32_t result_index = a-start;
111     if (_data.size() <= result_index) {
112       const int align = 0x1000;
113       uint32_t result_size = result_index + 1;  // size needed for result_index to be valid
114       uint32_t new_size = align_upwards(result_size, align);
115       // grow at least 2x to maintain some amortized complexity guarantees
116       if (new_size < _data.size() * 2)
117         new_size = _data.size() * 2;
118       // never grow past the stated limit
119       if (new_size > end-start)
120         new_size = end-start;
121       _data.resize(new_size);
122     }
123     return _data.at(result_index);
124   }
125   void grow_until(uint32_t new_end_address) {
126     if (new_end_address < end) return;
127     // Ugly: vma knows about the global Memory list of vmas
128     void sanity_check(uint32_t start, uint32_t end);
129     sanity_check(start, new_end_address);
130     end = new_end_address;
131   }
132   // End vma Methods
133 };
134 :(code)
135 void sanity_check(uint32_t start, uint32_t end) {
136   bool dup_found = false;
137   for (int i = 0;  i < SIZE(Mem);  ++i) {
138     const vma& curr = Mem.at(i);
139     if (curr.start == start) {
140       assert(!dup_found);
141       dup_found = true;
142     }
143     else if (curr.start > start) {
144       assert(curr.start > end);
145     }
146     else if (curr.start < start) {
147       assert(curr.end < start);
148     }
149   }
150 }
151 
152 :(before "End Globals")
153 // RAM is made of VMAs.
154 vector<vma> Mem;
155 :(code)
156 :(before "End Globals")
157 uint32_t End_of_program = 0;  // when the program executes past this address in tests we'll stop the test
158 // The stack grows downward. Can't increase its size for now.
159 :(before "End Reset")
160 Mem.clear();
161 End_of_program = 0;
162 :(code)
163 // These helpers depend on Mem being laid out contiguously (so you can't use a
164 // map, etc.) and on the host also being little-endian.
165 inline uint8_t read_mem_u8(uint32_t addr) {
166   uint8_t* handle = mem_addr_u8(addr);  // error messages get printed here
167   return handle ? *handle : 0;
168 }
169 inline int8_t read_mem_i8(uint32_t addr) {
170   return static_cast<int8_t>(read_mem_u8(addr));
171 }
172 inline uint32_t read_mem_u32(uint32_t addr) {
173   uint32_t* handle = mem_addr_u32(addr);  // error messages get printed here
174   return handle ? *handle : 0;
175 }
176 inline int32_t read_mem_i32(uint32_t addr) {
177   return static_cast<int32_t>(read_mem_u32(addr));
178 }
179 
180 inline uint8_t* mem_addr_u8(uint32_t addr) {
181   uint8_t* result = NULL;
182   for (int i = 0;  i < SIZE(Mem);  ++i) {
183     if (Mem.at(i).match(addr)) {
184       if (result)
185         raise << "address 0x" << HEXWORD << addr << " is in two segments\n" << end();
186       result = &Mem.at(i).data(addr);
187     }
188   }
189   if (result == NULL) {
190     if (Trace_file) Trace_file.flush();
191     raise << "Tried to access uninitialized memory at address 0x" << HEXWORD << addr << '\n' << end();
192     exit(1);
193   }
194   return result;
195 }
196 inline int8_t* mem_addr_i8(uint32_t addr) {
197   return reinterpret_cast<int8_t*>(mem_addr_u8(addr));
198 }
199 inline uint32_t* mem_addr_u32(uint32_t addr) {
200   uint32_t* result = NULL;
201   for (int i = 0;  i < SIZE(Mem);  ++i) {
202     if (Mem.at(i).match32(addr)) {
203       if (result)
204         raise << "address 0x" << HEXWORD << addr << " is in two segments\n" << end();
205       result = reinterpret_cast<uint32_t*>(&Mem.at(i).data(addr));
206     }
207   }
208   if (result == NULL) {
209     if (Trace_file) Trace_file.flush();
210     raise << "Tried to access uninitialized memory at address 0x" << HEXWORD << addr << '\n' << end();
211     raise << "The entire 4-byte word should be initialized and lie in a single segment.\n" << end();
212     exit(1);
213   }
214   return result;
215 }
216 inline int32_t* mem_addr_i32(uint32_t addr) {
217   return reinterpret_cast<int32_t*>(mem_addr_u32(addr));
218 }
219 // helper for some syscalls. But read-only.
220 inline const char* mem_addr_kernel_string(uint32_t addr) {
221   return reinterpret_cast<const char*>(mem_addr_u8(addr));
222 }
223 inline string mem_addr_string(uint32_t addr, uint32_t size) {
224   ostringstream out;
225   for (size_t i = 0;  i < size;  ++i)
226     out << read_mem_u8(addr+i);
227   return out.str();
228 }
229 
230 
231 inline void write_mem_u8(uint32_t addr, uint8_t val) {
232   uint8_t* handle = mem_addr_u8(addr);
233   if (handle != NULL) *handle = val;
234 }
235 inline void write_mem_i8(uint32_t addr, int8_t val) {
236   int8_t* handle = mem_addr_i8(addr);
237   if (handle != NULL) *handle = val;
238 }
239 inline void write_mem_u32(uint32_t addr, uint32_t val) {
240   uint32_t* handle = mem_addr_u32(addr);
241   if (handle != NULL) *handle = val;
242 }
243 inline void write_mem_i32(uint32_t addr, int32_t val) {
244   int32_t* handle = mem_addr_i32(addr);
245   if (handle != NULL) *handle = val;
246 }
247 
248 inline bool already_allocated(uint32_t addr) {
249   bool result = false;
250   for (int i = 0;  i < SIZE(Mem);  ++i) {
251     if (Mem.at(i).match(addr)) {
252       if (result)
253         raise << "address 0x" << HEXWORD << addr << " is in two segments\n" << end();
254       result = true;
255     }
256   }
257   return result;
258 }
259 
260 //:: core interpreter loop
261 
262 :(code)
263 // skeleton of how x86 instructions are decoded
264 void run_one_instruction() {
265   uint8_t op=0, op2=0, op3=0;
266   // Run One Instruction
267   if (Trace_file) {
268     dump_registers();
269     // End Dump Info for Instruction
270   }
271   uint32_t inst_start_address = EIP;
272   op = next();
273   trace(Callstack_depth+1, "run") << "0x" << HEXWORD << inst_start_address << " opcode: " << HEXBYTE << NUM(op) << end();
274   switch (op) {
275   case 0xf4:  // hlt
276     EIP = End_of_program;
277     break;
278   // End Single-Byte Opcodes
279   case 0x0f:
280     switch(op2 = next()) {
281     // End Two-Byte Opcodes Starting With 0f
282     default:
283       cerr << "unrecognized second opcode after 0f: " << HEXBYTE << NUM(op2) << '\n';
284       exit(1);
285     }
286     break;
287   case 0xf2:
288     switch(op2 = next()) {
289     // End Two-Byte Opcodes Starting With f2
290     case 0x0f:
291       switch(op3 = next()) {
292       // End Three-Byte Opcodes Starting With f2 0f
293       default:
294         cerr << "unrecognized third opcode after f2 0f: " << HEXBYTE << NUM(op3) << '\n';
295         exit(1);
296       }
297       break;
298     default:
299       cerr << "unrecognized second opcode after f2: " << HEXBYTE << NUM(op2) << '\n';
300       exit(1);
301     }
302     break;
303   case 0xf3:
304     switch(op2 = next()) {
305     // End Two-Byte Opcodes Starting With f3
306     case 0x0f:
307       switch(op3 = next()) {
308       // End Three-Byte Opcodes Starting With f3 0f
309       default:
310         cerr << "unrecognized third opcode after f3 0f: " << HEXBYTE << NUM(op3) << '\n';
311         exit(1);
312       }
313       break;
314     default:
315       cerr << "unrecognized second opcode after f3: " << HEXBYTE << NUM(op2) << '\n';
316       exit(1);
317     }
318     break;
319   default:
320     cerr << "unrecognized opcode: " << HEXBYTE << NUM(op) << '\n';
321     exit(1);
322   }
323 }
324 
325 inline uint8_t next() {
326   return read_mem_u8(EIP++);
327 }
328 
329 void dump_registers() {
330   ostringstream out;
331   out << "regs: ";
332   for (int i = 0;  i < NUM_INT_REGISTERS;  ++i) {
333     if (i > 0) out << "  ";
334     out << i << ": " << std::hex << std::setw(8) << std::setfill('_') << Reg[i].u;
335   }
336   out << " -- SF: " << SF << "; ZF: " << ZF << "; CF: " << CF << "; OF: " << OF;
337   trace(Callstack_depth+1, "run") << out.str() << end();
338 }
339 
340 //: start tracking supported opcodes
341 :(before "End Globals")
342 map</*op*/string, string> Name;
343 map</*op*/string, string> Name_0f;
344 map</*op*/string, string> Name_f3;
345 map</*op*/string, string> Name_f3_0f;
346 :(before "End One-time Setup")
347 init_op_names();
348 :(code)
349 void init_op_names() {
350   put(Name, "f4", "halt (hlt)");
351   // End Initialize Op Names
352 }
353 
354 :(before "End Help Special-cases(key)")
355 if (key == "opcodes") {
356   cerr << "Opcodes currently supported by SubX:\n";
357   for (map<string, string>::iterator p = Name.begin();  p != Name.end();  ++p)
358     cerr << "  " << p->first << ": " << p->second << '\n';
359   for (map<string, string>::iterator p = Name_0f.begin();  p != Name_0f.end();  ++p)
360     cerr << "  0f " << p->first << ": " << p->second << '\n';
361   for (map<string, string>::iterator p = Name_f3.begin();  p != Name_f3.end();  ++p)
362     cerr << "  f3 " << p->first << ": " << p->second << '\n';
363   for (map<string, string>::iterator p = Name_f3_0f.begin();  p != Name_f3_0f.end();  ++p)
364     cerr << "  f3 0f " << p->first << ": " << p->second << '\n';
365   cerr << "Run `bootstrap help instructions` for details on words like 'r32' and 'disp8'.\n"
366           "For complete details on these instructions, consult the IA-32 manual (volume 2).\n"
367           "There's various versions of it online, such as https://c9x.me/x86.\n"
368           "The mnemonics in brackets will help you locate each instruction.\n";
369   return 0;
370 }
371 :(before "End Help Contents")
372 cerr << "  opcodes\n";
373 
374 //: Helpers for managing trace depths
375 //:
376 //: We're going to use trace depths primarily to segment code running at
377 //: different frames of the call stack. This will make it easy for the trace
378 //: browser to collapse over entire calls.
379 //:
380 //: Errors will be at depth 0.
381 //: Warnings will be at depth 1.
382 //: SubX instructions will occupy depth 2 and up to Max_depth, organized by
383 //: stack frames. Each instruction's internal details will be one level deeper
384 //: than its 'main' depth. So 'call' instruction details will be at the same
385 //: depth as the instructions of the function it calls.
386 :(before "End Globals")
387 extern const int Initial_callstack_depth = 2;
388 int Callstack_depth = Initial_callstack_depth;
389 :(before "End Reset")
390 Callstack_depth = Initial_callstack_depth;
391 
392 :(before "End Includes")
393 #include <iomanip>
394 #define HEXBYTE  std::hex << std::setw(2) << std::setfill('0')
395 #define HEXWORD  std::hex << std::setw(8) << std::setfill('0')
396 // ugly that iostream doesn't print uint8_t as an integer
397 #define NUM(X) static_cast<int>(X)
398 #include <stdint.h>