4520 - several syscalls for files

4 files changed, 180 insertions, 0 deletions

diff --git a/subx/010---vm.cc b/subx/010---vm.cc
index 5bdd1dd1..33ebe51a 100644
--- a/subx/010---vm.cc
+++ b/subx/010---vm.cc
@@ -120,6 +120,9 @@ inline uint8_t* mem_addr_u8(uint32_t addr) {
 inline int8_t* mem_addr_i8(uint32_t addr) {
   return reinterpret_cast<int8_t*>(&Mem.at(addr-Mem_offset));
 }
+inline char* mem_addr_string(uint32_t addr) {
+  return reinterpret_cast<char*>(&Mem.at(addr-Mem_offset));
+}
 inline uint32_t* mem_addr_u32(uint32_t addr) {
   return reinterpret_cast<uint32_t*>(&Mem.at(addr-Mem_offset));
 }
diff --git a/subx/020syscalls.cc b/subx/020syscalls.cc
index 177ba6f1..2f6ca994 100644
--- a/subx/020syscalls.cc
+++ b/subx/020syscalls.cc
@@ -21,12 +21,90 @@ void process_int80() {
     exit(/*exit code*/Reg[EBX].u);
     break;
   case 3:
+    trace(91, "run") << "read: " << Reg[EBX].u << ' ' << Reg[ECX].u << '/' << mem_addr_string(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(91, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
     break;
   case 4:
+    trace(91, "run") << "write: " << Reg[EBX].u << ' ' << 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(91, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
+    break;
+  case 5: {
+    check_flags(ECX);
+    check_mode(EDX);
+    trace(91, "run") << "open: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << ' ' << Reg[ECX].u << end();
+    Reg[EAX].i = open(/*filename*/mem_addr_string(Reg[EBX].u), /*flags*/Reg[ECX].u, /*mode*/0640);
+    trace(91, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
+    break;
+  }
+  case 6:
+    trace(91, "run") << "close: " << Reg[EBX].u << end();
+    Reg[EAX].i = close(/*file descriptor*/Reg[EBX].u);
+    trace(91, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
+    break;
+  case 8:
+    check_mode(ECX);
+    trace(91, "run") << "creat: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << end();
+    Reg[EAX].i = creat(/*filename*/mem_addr_string(Reg[EBX].u), /*mode*/0640);
+    trace(91, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
+    break;
+  case 10:
+    trace(91, "run") << "unlink: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << end();
+    Reg[EAX].i = unlink(/*filename*/mem_addr_string(Reg[EBX].u));
+    trace(91, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
+    break;
+  case 38:
+    trace(91, "run") << "rename: " << Reg[EBX].u << '/' << mem_addr_string(Reg[EBX].u) << " -> " << Reg[ECX].u << '/' << mem_addr_string(Reg[ECX].u) << end();
+    Reg[EAX].i = rename(/*old filename*/mem_addr_string(Reg[EBX].u), /*new filename*/mem_addr_string(Reg[ECX].u));
+    trace(91, "run") << "result: " << Reg[EAX].i << end();
+    if (Reg[EAX].i == -1) raise << strerror(errno) << '\n' << end();
+    break;
+  case 45:  // brk: modify size of data segment
+    trace(91, "run") << "grow data segment to " << Reg[EBX].u << end();
+    resize_mem(/*new end address*/Reg[EBX].u);
     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))) {
+    raise << 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" << end();
+    exit(1);
+  }
+  if ((flags & O_RDONLY) && (flags & O_WRONLY)) {
+    raise << 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" << end();
+    exit(1);
+  }
+}
+
+void check_mode(int reg) {
+  if (Reg[reg].u != 0600) {
+    raise << HEXWORD << EIP << ": SubX is oblivious to file permissions; register " << reg << " must be 0.\n" << end();
+    exit(1);
+  }
+}
+
+void resize_mem(uint32_t new_end_address) {
+  if (new_end_address < Mem_offset) {
+    raise << HEXWORD << EIP << ": can't shrink data segment to before code segment\n";
+    return;
+  }
+  int32_t new_size = new_end_address - Mem_offset;
+  if (new_size < SIZE(Mem)) {
+    raise << HEXWORD << EIP << ": shrinking data segment is not supported.\n" << end();
+    return;
+  }
+  Mem.resize(new_size);  // will throw exception on failure
+}
diff --git a/subx/ex8 b/subx/ex8
new file mode 100755
index 00000000..d756271e
--- /dev/null
+++ b/subx/ex8
Binary files differdiff --git a/subx/ex8.subx b/subx/ex8.subx
new file mode 100644
index 00000000..0512157f
--- /dev/null
+++ b/subx/ex8.subx
@@ -0,0 +1,99 @@
+## example showing file syscalls
+# Create a file, open it for writing, write a character to it, close it, open
+# it for reading, read a character from it, close it, delete it, and return
+# the character read.
+#
+# To run:
+#   $ subx translate ex8.subx ex8
+#   $ subx run ex8
+# Expected result:
+#   $ echo $?
+#   97
+
+== 0x08048074  # code segment, after leaving room for ELF header and segment headers
+# instruction                     effective address                                                   operand     displacement    immediate
+# op          subop               mod             rm32          base        index         scale       r32
+# 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes
+
+  ## creat(filename)
+  bb/copy                         .               .             .           .             .           .           .               0x08049131/imm32/fname  # copy to EBX
+  b9/copy                         .               .             .           .             .           .           .               0x180/imm32/fixed-perms # copy 0 to ECX
+  b8/copy                         .               .             .           .             .           .           .               8/imm32/creat           # copy 8 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+
+  ## fd = open(filename, O_WRONLY, 0)
+  bb/copy                         .               .             .           .             .           .           .               0x08049131/imm32/fname  # copy to EBX
+  b9/copy                         .               .             .           .             .           .           .               1/imm32/wronly          # copy 1 to ECX
+  ba/copy                         .               .             .           .             .           .           .               0x180/imm32/fixed-perms # copy 0 to EDX
+  b8/copy                         .               .             .           .             .           .           .               5/imm32/open            # copy 5 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+  # save fd
+  bb/copy                         .               .             .           .             .           .           .               0x08049125/imm32/fd     # copy to EBX
+  89/copy                         0/mod/indirect  3/rm32/EBX                                          0/r32/EAX                                           # copy EAX to *EBX
+
+  ## write(fd, "a", 1)
+  # load fd
+  bb/copy                         .               .             .           .             .           .           .               0x08049125/imm32/fd     # copy to EBX
+  8b/copy                         0/mod/indirect  3/rm32/EBX                                          3/r32/EBX                                           # copy *EBX to EBX
+  #
+  b9/copy                         .               .             .           .             .           .           .               0x08049129/imm32/a      # copy to ECX
+  ba/copy                         .               .             .           .             .           .           .               1/imm32/size            # copy 1 to EDX
+  b8/copy                         .               .             .           .             .           .           .               4/imm32/write           # copy 4 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+
+  ## close(fd)
+  # load fd
+  bb/copy                         .               .             .           .             .           .           .               0x08049125/imm32/fd     # copy to EBX
+  8b/copy                         0/mod/indirect  3/rm32/EBX                                          3/r32/EBX                                           # copy *EBX to EBX
+  #
+  b8/copy                         .               .             .           .             .           .           .               6/imm32/close           # copy 6 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+
+  ## fd = open(filename, O_RDONLY, 0)
+  bb/copy                         .               .             .           .             .           .           .               0x08049131/imm32/fname  # copy to EBX
+  b9/copy                         .               .             .           .             .           .           .               0/imm32/rdonly          # copy 0 to ECX
+  ba/copy                         .               .             .           .             .           .           .               0x180/imm32/fixed-perms # copy 0 to EDX
+  b8/copy                         .               .             .           .             .           .           .               5/imm32/open            # copy 5 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+  # save fd
+  bb/copy                         .               .             .           .             .           .           .               0x08049125/imm32/fd     # copy to EBX
+  89/copy                         0/mod/indirect  3/rm32/EBX                                          0/r32/EAX                                           # copy EAX to *EBX
+
+  ## read(fd, b, 1)
+  # load fd
+  bb/copy                         .               .             .           .             .           .           .               0x08049125/imm32/fd     # copy to EBX
+  8b/copy                         0/mod/indirect  3/rm32/EBX                                          3/r32/EBX                                           # copy *EBX to EBX
+  #
+  b9/copy                         .               .             .           .             .           .           .               0x0804912d/imm32/b      # copy to ECX
+  ba/copy                         .               .             .           .             .           .           .               1/imm32/size            # copy 1 to EDX
+  b8/copy                         .               .             .           .             .           .           .               3/imm32/read            # copy 3 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+
+  ## close(fd)
+  # load fd
+  bb/copy                         .               .             .           .             .           .           .               0x08049125/imm32/fd     # copy to EBX
+  8b/copy                         0/mod/indirect  3/rm32/EBX                                          3/r32/EBX                                           # copy *EBX to EBX
+  #
+  b8/copy                         .               .             .           .             .           .           .               6/imm32/close           # copy 8 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+
+  ## unlink(filename)
+  bb/copy                         .               .             .           .             .           .           .               0x08049131/imm32/fname  # copy to EBX
+  b8/copy                         .               .             .           .             .           .           .               0xa/imm32/unlink        # copy 8 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+
+  ## exit(b)
+  # load b
+  bb                              .               .             .           .             .           .           .               0x0804912d/imm32/b      # copy to EBX
+  8b/copy                         0/mod/indirect  3/rm32/EBX                                          3/r32/EBX                                           # copy *EBX to EBX
+  #
+  b8/copy                         .               .             .           .             .           .           .               1/imm32/exit            # copy 1 to EAX
+  cd/syscall                      .               .             .           .             .           .           .               0x80/imm8               # int 80h
+
+== 0x08049125  # data segment
+00 00 00 00  # fd
+61 00 00 00  # a: string to write to file: 'a'
+00 00 00 00  # b: space for string read from file
+2e 66 6f 6f 00 00 00 00  # filename: '.foo'
+
+# vim:ft=subx:nowrap:tw&