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 MMX, etc.
  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 Types")
 32 const int NUM_XMM_REGISTERS = 8;
 33 float Xmm[NUM_XMM_REGISTERS] = { 0.0 };
 34 const string Xname[NUM_XMM_REGISTERS] = { "XMM0", "XMM1", "XMM2", "XMM3", "XMM4", "XMM5", "XMM6", "XMM7" };
 35 :(before "End Reset")
 36 bzero(Xmm, sizeof(Xmm));
 37 
 38 :(before "End Help Contents")
 39 cerr << "  registers\n";
 40 :(before "End Help Texts")
 41 put_new(Help, "registers",
 42   "SubX supports 16 registers: eight 32-bit integer registers and eight single-precision\n"
 43   "floating-point registers. From 0 to 7, they are:\n"
 44   "  integer: EAX ECX EDX EBX ESP EBP ESI EDI\n"
 45   "  floating point: XMM0 XMM1 XMM2 XMM3 XMM4 XMM5 XMM6 XMM7\n"
 46   "ESP contains the top of the stack.\n"
 47   "\n"
 48   "-- 8-bit registers\n"
 49   "Some instructions operate on eight *overlapping* 8-bit registers.\n"
 50   "From 0 to 7, they are:\n"
 51   "  AL CL DL BL AH CH DH BH\n"
 52   "The 8-bit registers overlap with the 32-bit ones. AL is the lowest signicant byte\n"
 53   "of EAX, AH is the second lowest significant byte, and so on.\n"
 54   "\n"
 55   "For example, if EBX contains 0x11223344, then BL contains 0x44, and BH contains 0x33.\n"
 56   "\n"
 57   "There is no way to access bytes within ESP, EBP, ESI or EDI.\n"
 58   "\n"
 59   "For complete details consult the IA-32 software developer's manual, volume 2,\n"
 60   "table 2-2, \"32-bit addressing forms with the ModR/M byte\".\n"
 61   "It is included in this repository as 'modrm.pdf'.\n"
 62   "The register encodings are described in the top row of the table, but you'll need\n"
 63   "to spend some time with it.\n"
 64   "\n"
 65   "-- flag registers\n"
 66   "Various instructions (particularly 'compare') modify one or more of four 1-bit\n"
 67   "'flag' registers, as a side-effect:\n"
 68   "- the sign flag (SF): usually set if an arithmetic result is negative, or\n"
 69   "  reset if not.\n"
 70   "- the zero flag (ZF): usually set if a result is zero, or reset if not.\n"
 71   "- the carry flag (CF): usually set if an arithmetic result overflows by just one bit.\n"
 72   "  Useful for operating on unsigned numbers.\n"
 73   "- the overflow flag (OF): usually set if an arithmetic result overflows by more\n"
 74   "  than one bit. Useful for operating on signed numbers.\n"
 75   "The flag bits are read by conditional jumps.\n"
 76   "\n"
 77   "For complete details on how different instructions update the flags, consult the IA-32\n"
 78   "manual (volume 2). There's various versions of it online, such as https://c9x.me/x86,\n"
 79   "though of course you'll need to be careful to ignore instructions and flag registers\n"
 80   "that SubX doesn't support.\n"
 81   "\n"
 82   "It isn't simple, but if this is the processor you have running on your computer.\n"
 83   "Might as well get good at it.\n"
 84 );
 85 
 86 :(before "End Globals")
 87 // the subset of x86 flag registers we care about
 88 bool SF = false;  // sign flag
 89 bool ZF = false;  // zero flag
 90 bool CF = false;  // carry flag
 91 bool OF = false;  // overflow flag
 92 :(before "End Reset")
 93 SF = ZF = CF = OF = false;
 94 
 95 //:: simulated RAM
 96 
 97 :(before "End Types")
 98 const uint32_t SEGMENT_ALIGNMENT = 0x1000000;  // 16MB
 99 inline uint32_t align_upwards(uint32_t x, uint32_t align) {
100   return (x+align-1) & -(align);
101 }
102 
103 // Like in real-world Linux, we'll allocate RAM for our programs in disjoint
104 // slabs called VMAs or Virtual Memory Areas.
105 struct vma {
106   uint32_t start;  // inclusive
107   uint32_t end;  // exclusive
108   vector<uint8_t> _data;
109   vma(uint32_t s, uint32_t e) :start(s), end(e) {}
110   vma(uint32_t s) :start(s), end(align_upwards(s+1, SEGMENT_ALIGNMENT)) {}
111   bool match(uint32_t a) {
112     return a >= start && a < end;
113   }
114   bool match32(uint32_t a) {
115     return a >= start && a+4 <= end;
116   }
117   uint8_t& data(uint32_t a) {
118     assert(match(a));
119     uint32_t result_index = a-start;
120     if (_data.size() <= result_index+/*largest word size that can be accessed in one instruction*/sizeof(int)) {
121       const int align = 0x1000;
122       uint32_t result_size = result_index + 1;  // size needed for result_index to be valid
123       uint32_t new_size = align_upwards(result_size, align);
124       // grow at least 2x to maintain some amortized complexity guarantees
125       if (new_size < _data.size() * 2)
126         new_size = _data.size() * 2;
127       // never grow past the stated limit
128       if (new_size > end-start)
129         new_size = end-start;
130       _data.resize(new_size);
131     }
132     return _data.at(result_index);
133   }
134   void grow_until(uint32_t new_end_address) {
135     if (new_end_address < end) return;
136     // Ugly: vma knows about the global Memory list of vmas
137     void sanity_check(uint32_t start, uint32_t end);
138     sanity_check(start, new_end_address);
139     end = new_end_address;
140   }
141   // End vma Methods
142 };
143 :(code)
144 void sanity_check(uint32_t start, uint32_t end) {
145   bool dup_found = false;
146   for (int i = 0;  i < SIZE(Mem);  ++i) {
147     const vma& curr = Mem.at(i);
148     if (curr.start == start) {
149       assert(!dup_found);
150       dup_found = true;
151     }
152     else if (curr.start > start) {
153       assert(curr.start > end);
154     }
155     else if (curr.start < start) {
156       assert(curr.end < start);
157     }
158   }
159 }
160 
161 :(before "End Globals")
162 // RAM is made of VMAs.
163 vector<vma> Mem;
164 :(code)
165 :(before "End Globals")
166 uint32_t End_of_program = 0;  // when the program executes past this address in tests we'll stop the test
167 // The stack grows downward. Can't increase its size for now.
168 :(before "End Reset")
169 Mem.clear();
170 End_of_program = 0;
171 :(code)
172 // These helpers depend on Mem being laid out contiguously (so you can't use a
173 // map, etc.) and on the host also being little-endian.
174 inline uint8_t read_mem_u8(uint32_t addr) {
175   uint8_t* handle = mem_addr_u8(addr);  // error messages get printed here
176   return handle ? *handle : 0;
177 }
178 inline int8_t read_mem_i8(uint32_t addr) {
179   return static_cast<int8_t>(read_mem_u8(addr));
180 }
181 inline uint32_t read_mem_u32(uint32_t addr) {
182   uint32_t* handle = mem_addr_u32(addr);  // error messages get printed here
183   return handle ? *handle : 0;
184 }
185 inline int32_t read_mem_i32(uint32_t addr) {
186   return static_cast<int32_t>(read_mem_u32(addr));
187 }
188 inline float read_mem_f32(uint32_t addr) {
189   return static_cast<float>(read_mem_u32(addr));
190 }
191 
192 inline uint8_t* mem_addr_u8(uint32_t addr) {
193   uint8_t* result = NULL;
194   for (int i = 0;  i < SIZE(Mem);  ++i) {
195     if (Mem.at(i).match(addr)) {
196       if (result)
197         raise << "address 0x" << HEXWORD << addr << " is in two segments\n" << end();
198       result = &Mem.at(i).data(addr);
199     }
200   }
201   if (result == NULL) {
202     if (Trace_file.is_open()) Trace_file.flush();
203     raise << "Tried to access uninitialized memory at address 0x" << HEXWORD << addr << '\n' << end();
204     exit(1);
205   }
206   return result;
207 }
208 inline int8_t* mem_addr_i8(uint32_t addr) {
209   return reinterpret_cast<int8_t*>(mem_addr_u8(addr));
210 }
211 inline uint32_t* mem_addr_u32(uint32_t addr) {
212   uint32_t* result = NULL;
213   for (int i = 0;  i < SIZE(Mem);  ++i) {
214     if (Mem.at(i).match32(addr)) {
215       if (result)
216         raise << "address 0x" << HEXWORD << addr << " is in two segments\n" << end();
217       result = reinterpret_cast<uint32_t*>(&Mem.at(i).data(addr));
218     }
219   }
220   if (result == NULL) {
221     if (Trace_file.is_open()) Trace_file.flush();
222     raise << "Tried to access uninitialized memory at address 0x" << HEXWORD << addr << '\n' << end();
223     exit(1);
224   }
225   return result;
226 }
227 inline int32_t* mem_addr_i32(uint32_t addr) {
228   return reinterpret_cast<int32_t*>(mem_addr_u32(addr));
229 }
230 inline float* mem_addr_f32(uint32_t addr) {
231   return reinterpret_cast<float*>(mem_addr_u32(addr));
232 }
233 // helper for some syscalls. But read-only.
234 inline const char* mem_addr_kernel_string(uint32_t addr) {
235   return reinterpret_cast<const char*>(mem_addr_u8(addr));
236 }
237 inline string mem_addr_string(uint32_t addr, uint32_t sizec:character
    loop
  }
]

recipe wait-for-event [
  default-space:address:array:location <- new location:type, 30:literal
  console:address <- next-ingredient
  {
    _, console:address, found?:boolean <- read-event console:address
    loop-unless found?:boolean
  }
]