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:(before "End Initialize Op Names")
put_new(Name, "cd", "software interrupt (int)");
:(before "End Single-Byte Opcodes")
case 0xcd: { // int imm8 (software interrupt)
trace(Callstack_depth+1, "run") << "syscall" << end();
uint8_t code = next();
if (code != 0x80) {
raise << "Unimplemented interrupt code " << HEXBYTE << code << '\n' << end();
raise << " Only `int 80h` supported for now.\n" << end();
break;
}
process_int80();
break;
}
:(code)
void process_int80() {
switch (Reg[EAX].u) {
case 1:
exit(/*exit code*/Reg[EBX].u);
break;
case 3:
trace(Callstack_depth+1, "run") << "read: " << Reg[EBX].u << ' ' << Reg[ECX].u << ' ' << Reg[EDX].u << end();
Reg[EAX].i = read(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u);
trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
if (Reg[EAX].i == -1) raise << "read: " << strerror(errno) << '\n' << end();
break;
case 4:
trace(Callstack_depth+1, "run") << "write: " << Reg[EBX].u << ' ' << Reg[ECX].u << ' ' << Reg[EDX].u << end();
trace(Callstack_depth+1, "run") << Reg[ECX].u << " => " << mem_addr_string(Reg[ECX].u, Reg[EDX].u) << end();
Reg[EAX].i = write(/*file descriptor*/Reg[EBX].u, /*memory buffer*/mem_addr_u8(Reg[ECX].u), /*size*/Reg[EDX].u);
trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
if (Reg[EAX].i == -1) raise << "write: " << strerror(errno) << '\n' << end();
break;
case 5: {
check_flags(ECX);
check_mode(EDX);
trace(Callstack_depth+1, "run") << "open: " << Reg[EBX].u << ' ' << Reg[ECX].u << end();
trace(Callstack_depth+1, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
Reg[EAX].i = open(/*filename*/mem_addr_kernel_string(Reg[EBX].u), /*flags*/Reg[ECX].u, /*mode*/0640);
trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
if (Reg[EAX].i == -1) raise << "open: " << strerror(errno) << '\n' << end();
break;
}
case 6:
trace(Callstack_depth+1, "run") << "close: " << Reg[EBX].u << end();
Reg[EAX].i = close(/*file descriptor*/Reg[EBX].u);
trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
if (Reg[EAX].i == -1) raise << "close: " << strerror(errno) << '\n' << end();
break;
case 8:
check_mode(ECX);
trace(Callstack_depth+1, "run") << "creat: " << Reg[EBX].u << end();
trace(Callstack_depth+1, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
Reg[EAX].i = creat(/*filename*/mem_addr_kernel_string(Reg[EBX].u), /*mode*/0640);
trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
if (Reg[EAX].i == -1) raise << "creat: " << strerror(errno) << '\n' << end();
break;
case 10:
trace(Callstack_depth+1, "run") << "unlink: " << Reg[EBX].u << end();
trace(Callstack_depth+1, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
Reg[EAX].i = unlink(/*filename*/mem_addr_kernel_string(Reg[EBX].u));
trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
if (Reg[EAX].i == -1) raise << "unlink: " << strerror(errno) << '\n' << end();
break;
case 38:
trace(Callstack_depth+1, "run") << "rename: " << Reg[EBX].u << " -> " << Reg[ECX].u << end();
trace(Callstack_depth+1, "run") << Reg[EBX].u << " => " << mem_addr_kernel_string(Reg[EBX].u) << end();
trace(Callstack_depth+1, "run") << Reg[ECX].u << " => " << mem_addr_kernel_string(Reg[ECX].u) << end();
Reg[EAX].i = rename(/*old filename*/mem_addr_kernel_string(Reg[EBX].u), /*new filename*/mem_addr_kernel_string(Reg[ECX].u));
trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].i << end();
if (Reg[EAX].i == -1) raise << "rename: " << strerror(errno) << '\n' << end();
break;
case 90: // mmap: allocate memory outside existing segment allocations
trace(Callstack_depth+1, "run") << "mmap: allocate new segment" << end();
// Ignore most arguments for now: address hint, protection flags, sharing flags, fd, offset.
// We only support anonymous maps.
Reg[EAX].u = new_segment(/*length*/read_mem_u32(Reg[EBX].u+0x4));
trace(Callstack_depth+1, "run") << "result: " << Reg[EAX].u << end();
break;
default:
raise << HEXWORD << EIP << ": unimplemented syscall " << Reg[EAX].u << '\n' << end();
}
}
// SubX is oblivious to file permissions, directories, symbolic links, terminals, and much else besides.
// Also ignoring any concurrency considerations for now.
void check_flags(int reg) {
uint32_t flags = Reg[reg].u;
if (flags != ((flags & O_RDONLY) | (flags & O_WRONLY))) {
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";
exit(1);
}
if ((flags & O_RDONLY) && (flags & O_WRONLY)) {
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";
exit(1);
}
}
void check_mode(int reg) {
if (Reg[reg].u != 0600) {
cerr << HEXWORD << EIP << ": SubX is oblivious to file permissions; register " << reg << " must be 0x180.\n";
exit(1);
}
}
:(before "End Globals")
// Very primitive/fixed/insecure mmap segments for now.
uint32_t Segments_allocated_above = END_HEAP;
:(code)
// always allocate multiples of the segment size
uint32_t new_segment(uint32_t length) {
assert(length > 0);
uint32_t result = (Segments_allocated_above - length) & 0xff000000; // same number of zeroes as SEGMENT_ALIGNMENT
if (result <= START_HEAP) {
raise << "Allocated too many segments; the VM ran out of memory. "
<< "Maybe SEGMENT_ALIGNMENT can be smaller?\n" << die();
}
Mem.push_back(vma(result, result+length));
Segments_allocated_above = result;
return result;
}
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