# Mu - subx/020syscalls.cc

      1 :(before "End Initialize Op Names")
      2 put_new(Name, "cd", "software interrupt (int)");
      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 << ' ' << Reg[EDX].u << end();
     25     trace(91, "run") << Reg[ECX].u << " => " << mem_addr_string(Reg[ECX].u, Reg[EDX].u) << end();
     26     Reg[EAX].i = read(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u);
     27     trace(91, "run") << "result: " << Reg[EAX].i << end();
     28     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
     29     break;
     30   case 4:
     31     trace(91, "run") << "write: " << Reg[EBX].u << ' ' << Reg[ECX].u << ' ' << Reg[EDX].u << end();
     32     trace(91, "run") << Reg[ECX].u << " => " << mem_addr_string(Reg[ECX].u, Reg[EDX].u) << end();
     33     Reg[EAX].i = write(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u);
     34     trace(91, "run") << "result: " << Reg[EAX].i << end();
     35     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
     36     break;
     37   case 5: {
     38     check_flags(ECX);
     39     check_mode(EDX);
     40     trace(91, "run") << "open: " << Reg[EBX].u << ' ' << Reg[ECX].u << end();
     41     trace(91, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
     42     Reg[EAX].i = open(/*filename*/mem_addr_kernel_string(Reg[EBX].u), /*flags*/Reg[ECX].u, /*mode*/0640);
     43     trace(91, "run") << "result: " << Reg[EAX].i << end();
     44     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
     45     break;
     46   }
     47   case 6:
     48     trace(91, "run") << "close: " << Reg[EBX].u << end();
     49     Reg[EAX].i = close(/*file descriptor*/Reg[EBX].u);
     50     trace(91, "run") << "result: " << Reg[EAX].i << end();
     51     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
     52     break;
     53   case 8:
     54     check_mode(ECX);
     55     trace(91, "run") << "creat: " << Reg[EBX].u << end();
     56     trace(91, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
     57     Reg[EAX].i = creat(/*filename*/mem_addr_kernel_string(Reg[EBX].u), /*mode*/0640);
     58     trace(91, "run") << "result: " << Reg[EAX].i << end();
     59     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
     60     break;
     61   case 10:
     62     trace(91, "run") << "unlink: " << Reg[EBX].u << end();
     63     trace(91, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
     64     Reg[EAX].i = unlink(/*filename*/mem_addr_kernel_string(Reg[EBX].u));
     65     trace(91, "run") << "result: " << Reg[EAX].i << end();
     66     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
     67     break;
     68   case 38:
     69     trace(91, "run") << "rename: " << Reg[EBX].u << " -> " << Reg[ECX].u << end();
     70     trace(91, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
     71     trace(91, "run") << Reg[ECX].u << " => " << mem_addr_kernel_string(Reg[ECX].u) << end();
     72     Reg[EAX].i = rename(/*old filename*/mem_addr_kernel_string(Reg[EBX].u), /*new filename*/mem_addr_kernel_string(Reg[ECX].u));
     73     trace(91, "run") << "result: " << Reg[EAX].i << end();
     74     if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
     75     break;
     76   case 45:  // brk: modify size of data segment
     77     trace(91, "run") << "grow data segment to " << Reg[EBX].u << end();
     78     grow_data_segment(/*new end address*/Reg[EBX].u);
     79     break;
     80   case 90:  // mmap: allocate memory outside existing segment allocations
     81     trace(91, "run") << "mmap: allocate new segment" << end();
     82     // Ignore most arguments for now: address hint, protection flags, sharing flags, fd, offset.
     83     // We only support anonymous maps.
     84     Reg[EAX].u = new_segment(/*length*/read_mem_u32(Reg[EBX].u+0x4));
     85     trace(91, "run") << "result: " << Reg[EAX].u << end();
     86     break;
     87   default:
     88     raise << HEXWORD << EIP << ": unimplemented syscall " << Reg[EAX].u << '\n' << end();
     89   }
     90 }
     91
     92 // SubX is oblivious to file permissions, directories, symbolic links, terminals, and much else besides.
     93 // Also ignoring any concurrency considerations for now.
     94 void check_flags(int reg) {
     95   uint32_t flags = Reg[reg].u;
     96   if (flags != ((flags & O_RDONLY) | (flags & O_WRONLY))) {
     97     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";
     98     exit(1);
     99   }
    100   if ((flags & O_RDONLY) && (flags & O_WRONLY)) {
    101     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";
    102     exit(1);
    103   }
    104 }
    105
    106 void check_mode(int reg) {
    107   if (Reg[reg].u != 0600) {
    108     cerr << HEXWORD << EIP << ": SubX is oblivious to file permissions; register " << reg << " must be 0.\n";
    109     exit(1);
    110   }
    111 }
    112
    113 :(before "End Globals")
    114 uint32_t Next_segment = 0xb0000000;  // 0xc0000000 and up is reserved for Linux kernel
    115 const uint32_t SPACE_FOR_SEGMENT = 0x01000000;
    116 :(code)
    117 uint32_t new_segment(uint32_t length) {
    118   uint32_t result = Next_segment;
    119   Mem.push_back(vma(Next_segment, Next_segment+length));
    120   Next_segment -= SPACE_FOR_SEGMENT;
    121   return result;
    122 }