implemented syscalls open, read, write, close, exit

docs/syscalls.md

@@ -0,0 +1,46 @@
+# Syscalls:
+
+Performing a syscall is quite simple:
+```risc-v asm
+    ; set syscall code:
+    addi a7, zero, 93   ; or SCALL_EXIT if syscall symbols are mapped
+    ; set syscall args:
+    addi a0, zero, 1    ; exit with code 1
+    ; invode syscall handler
+    scall               
+```
+
+In order to use the global syscall symbols, run with the `--syscall-symbols` flag (not implemented yet)
+
+## Read (63) `SCALL_READ`
+* `a0`: source file descriptor
+* `a1`: addr in which to read
+* `a2`: number of bytes to read (at most)
+* `return: a0` number of bytes read or -1
+
+## Write (64) `SCALL_WRITE`
+* `a0`: target file descriptor
+* `a1`: addr from which to read
+* `a2`: number of bytes to read
+* `return: a0`: number of bytes written or -1
+
+## Exit (93) `SCALL_EXIT`
+* `a0`: exit code
+
+## Open (1024) `SCALL_OPEN`
+* `a0`: open mode:
+    - `0`: read
+    - `1`: write (truncate)
+    - `2`: read/write (no truncate)
+    - `3`: only create
+    - `4`: append
+* `a1`: addr where path is stored
+* `a2`: length of path
+* `return: a0`: file descriptor of opened file or -1
+
+Requires flag `--scall-fs` to be set to True
+
+## Close (1025) `SCALL_OPEN`
+* `a0`: file descriptor to close
+* `return: a0`: 0 if closed correctly or -1
+

riscemu/Syscall.py

@@ -1,6 +1,10 @@
 from dataclasses import dataclass
+from typing import Dict, IO
+import sys
+
 from .Registers import Registers
 from .Exceptions import InvalidSyscallException
+from .helpers import *
 
 import typing
 
@@ -8,9 +12,19 @@ if typing.TYPE_CHECKING:
     from . import CPU
 
 SYSCALLS = {
-    63: 'read',
-    64: 'write',
-    93: 'exit'
+    63:   'read',
+    64:   'write',
+    93:   'exit',
+    1024: 'open',
+    1025: 'close',
+}
+
+OPEN_MODES = {
+    0: 'rb',
+    1: 'wb',
+    2: 'r+b',
+    3: 'x',
+    4: 'ab',
 }
 
 
@@ -29,19 +43,124 @@ class Syscall:
             self.id, self.name
         )
 
+    def ret(self, code):
+        self.registers.set('a0', code)
 
 class SyscallInterface:
+    open_files: Dict[int, IO]
+    next_open_handle: int
+
     def handle_syscall(self, scall: Syscall):
+        self.next_open_handle = 3
+        self.open_files = {
+            0: sys.stdin,
+            1: sys.stdout,
+            2: sys.stderr
+        }
+
         if getattr(self, scall.name):
             getattr(self, scall.name)(scall)
         else:
             raise InvalidSyscallException(scall)
 
     def read(self, scall: Syscall):
-        pass
+        """
+        read syscall (63): read from file no a0, into addr a1, at most a2 bytes
+        on return a0 will be the number of read bytes or -1 if an error occured
+        """
+        fileno = scall.registers.get('a0')
+        addr = scall.registers.get('a1')
+        len = scall.registers.get('a2')
+        if fileno not in self.open_files:
+            scall.registers.set('a0', -1)
+            return
+
+        chars = self.open_files[fileno].read(len)
+        try:
+            data = bytearray(chars, 'ascii')
+            scall.cpu.mmu.write(addr, len(data), data)
+            return scall.ret(len(data))
+
+        except UnicodeEncodeError:
+            print(FMT_ERROR + '[Syscall] read: UnicodeError - invalid input "{}"'.format(chars) + FMT_NONE)
+            return scall.ret(-1)
 
     def write(self, scall: Syscall):
-        pass
+        """
+        write syscall (64): write a2 bytes from addr a1 into fileno a0
+        on return a0 will hold the number of bytes written or -1 if an error occured
+        """
+        fileno = scall.registers.get('a0')
+        addr = scall.registers.get('a1')
+        size = scall.registers.get('a2')
+        if fileno not in self.open_files:
+            return scall.ret(-1)
+
+        data = scall.cpu.mmu.read(addr, size)
+
+        if not isinstance(str, bytearray):
+            print(FMT_ERROR + '[Syscall] write: writing from .text region not supported.' + FMT_NONE)
+            return scall.ret(-1)
+
+        self.open_files[fileno].write(data.decode('ascii'))
+        return scall.ret(size)
+
+    def open(self, scall: Syscall):
+        """
+        open syscall (1024): read path of a2 bytes from addr a1, in mode a0
+        returns the file no in a0
+
+        modes:
+            - 0: read
+            - 1: write (truncate)
+            - 2: read/write (no truncate)
+            - 3: only create
+            - 4: append
+
+        Requires running with flag scall-fs
+        """
+        if not scall.cpu.conf.scall_fs:
+            print(FMT_ERROR + '[Syscall] open: opening files not supported without scall-fs flag!' + FMT_NONE)
+            return scall.ret(-1)
+
+        mode = scall.registers.get('a0')
+        addr = scall.registers.get('a1')
+        size = scall.registers.get('a2')
+
+        mode_st = OPEN_MODES.get(mode, )
+        if mode_st == -1:
+            print(FMT_ERROR + '[Syscall] open: unknown opening mode {}!'.format(mode) + FMT_NONE)
+            return scall.ret(-1)
+
+        path = scall.cpu.mmu.read(addr, size).decode('ascii')
+
+        fileno = self.next_open_handle
+        self.next_open_handle += 1
+
+        try:
+            self.open_files[fileno] = open(path, mode_st)
+        except OSError as err:
+            print(FMT_ERROR + '[Syscall] open: encountered error during {}!'.format(err.strerror) + FMT_NONE)
+            return scall.ret(-1)
+
+        print(FMT_CYAN + '[Syscall] open: opened fd {} to {}!'.format(fileno, path) + FMT_NONE)
+        return scall.ret(fileno)
+
+    def close(self, scall: Syscall):
+        """
+        close syscall (1025): closes file no a0
+
+        return -1 if an error was encountered, otherwise returns 0
+        """
+        fileno = scall.registers.get('a0')
+        if fileno not in self.open_files:
+            print(FMT_ERROR + '[Syscall] close: unknown fileno {}!'.format(fileno) + FMT_NONE)
+            return scall.ret(-1)
+
+        self.open_files[fileno].close()
+        print(FMT_CYAN + '[Syscall] close: closed fd {}!'.format(fileno) + FMT_NONE)
+        del self.open_files[fileno]
+        return scall.ret(0)
 
     def exit(self, scall: Syscall):
         scall.cpu.exit = True

riscemu/helpers.py

@@ -43,6 +43,7 @@ def int_from_bytes(bytes, unsigned=False):
 
 # Colors
 
+FMT_RED = '\033[31m'
 FMT_ORANGE = '\033[33m'
 FMT_GRAY = '\033[37m'
 FMT_CYAN = '\033[36m'
@@ -51,3 +52,5 @@ FMT_BOLD = '\033[1m'
 FMT_MAGENTA = '\033[35m'
 FMT_NONE = '\033[0m'
 FMT_UNDERLINE = '\033[4m'
+
+FMT_ERROR = FMT_RED + FMT_BOLD