1 :(before "End Initialize Op Names(name)")
  2 put(name, "cd", "software interrupt");
  3 
  4 :(before "End Single-Byte Opcodes")
  5 case 0xcd: {  // int imm8 (software interrupt)
  6   trace(90, "run") << "syscall" << end();
  7   uint8_t code = next();
  8   if (code != 0x80) {
  9     raise << "Unimplemented interrupt code " << HEXBYTE << code << '\n' << end();
 10     raise << "  Only `int 80h` supported for now.\n" << end();
 11     break;
 12   }
 13   process_int80();
 14   break;
 15 }
 16 
 17 :(code)
 18 void process_int80() {
 19   switch (Reg[EAX].u) {
 20   case 1:
 21     exit(/*exit code*/Reg[EBX].u);
 22     break;
 23   case 3:
 24     trace(91, "run") << "read: " << Reg[EBX].u << ' ' << Reg[ECX].u << '/' << mem_addr_string(Reg[ECX].u) << ' ' << Reg[EDX].u << end();
 25     Reg[EAX].i = read(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u);
 26     trace(91, "run") << "result: " << Reg[EAX].i << end();
 27     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
 28     break;
 29   case 4:
 30     trace(91, "run") << "write: " << Reg[EBX].u << ' ' << Reg[ECX].u << '/' << mem_addr_string(Reg[ECX].u) << ' ' << Reg[EDX].u << end();
 31     Reg[EAX].i = write(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u);
 32     trace(91, "run") << "result: " << Reg[EAX].i << end();
 33     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
 34     break;
 35   case 5: {
 36     check_flags(ECX);
 37     check_mode(EDX);
 38     trace(91, "run") << "open: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << ' ' << Reg[ECX].u << end();
 39     Reg[EAX].i = open(/*filename*/mem_addr_string(Reg[EBX].u), /*flags*/Reg[ECX].u, /*mode*/0640);
 40     trace(91, "run") << "result: " << Reg[EAX].i << end();
 41     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
 42     break;
 43   }
 44   case 6:
 45     trace(91, "run") << "close: " << Reg[EBX].u << end();
 46     Reg[EAX].i = close(/*file descriptor*/Reg[EBX].u);
 47     trace(91, "run") << "result: " << Reg[EAX].i << end();
 48     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
 49     break;
 50   case 8:
 51     check_mode(ECX);
 52     trace(91, "run") << "creat: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << end();
 53     Reg[EAX].i = creat(/*filename*/mem_addr_string(Reg[EBX].u), /*mode*/0640);
 54     trace(91, "run") << "result: " << Reg[EAX].i << end();
 55     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
 56     break;
 57   case 10:
 58     trace(91, "run") << "unlink: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << end();
 59     Reg[EAX].i = unlink(/*filename*/mem_addr_string(Reg[EBX].u));
 60     trace(91, "run") << "result: " << Reg[EAX].i << end();
 61     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
 62     break;
 63   case 38:
 64     trace(91, "run") << "rename: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << " -> " << Reg[ECX].u << '/' << mem_addr_string(Reg[ECX].u) << end();
 65     Reg[EAX].i = rename(/*old filename*/mem_addr_string(Reg[EBX].u), /*new filename*/mem_addr_string(Reg[ECX].u));
 66     trace(91, "run") << "result: " << Reg[EAX].i << end();
 67     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
 68     break;
 69   case 45:  // brk: modify size of data segment
 70     trace(91, "run") << "grow data segment to " << Reg[EBX].u << end();
 71     resize_mem(/*new end address*/Reg[EBX].u);
 72     break;
 73   default:
 74     raise << HEXWORD << EIP << ": unimplemented syscall " << Reg[EAX].u << '\n' << end();
 75   }
 76 }
 77 
 78 // SubX is oblivious to file permissions, directories, symbolic links, terminals, and much else besides.
 79 // Also ignoring any concurrency considerations for now.
 80 void check_flags(int reg) {
 81   uint32_t flags = Reg[reg].u;
 82   if (flags != ((flags & O_RDONLY) | (flags & O_WRONLY))) {
 83     cerr << HEXWORD << EIP << ": most POSIX flags to the open() syscall are not supported. Just O_RDONLY and O_WRONLY for now. Zero concurrent access support.\n";
 84     exit(1);
 85   }
 86   if ((flags & O_RDONLY) && (flags & O_WRONLY)) {
 87     cerr << HEXWORD << EIP << ": can't open a file for both reading and writing at once. See http://man7.org/linux/man-pages/man2/open.2.html.\n";
 88     exit(1);
 89   }
 90 }
 91 
 92 void check_mode(int reg) {
 93   if (Reg[reg].u != 0600) {
 94     cerr << HEXWORD << EIP << ": SubX is oblivious to file permissions; register " << reg << " must be 0.\n";
 95     exit(1);
 96   }
 97 }
 98 
 99 void resize_mem(uint32_t new_end_address) {
100   if (new_end_address < Mem_offset) {
101     raise << HEXWORD << EIP << ": can't shrink data segment to before code segment\n";
102     return;
103   }
104   int32_t new_size = new_end_address - Mem_offset;
105   if (new_size < SIZE(Mem)) {
106     raise << HEXWORD << EIP << ": shrinking data segment is not supported.\n" << end();
107     return;
108   }
109   Mem.resize(new_size);  // will throw exception on failure
110 }