/
runtime.go
126 lines (109 loc) · 2.81 KB
/
runtime.go
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package vm
import (
"errors"
"fmt"
"github.com/dnsge/orange/arch"
"log"
)
const (
syscallRead = 0
syscallWrite = 1
)
var (
ErrInvalidFileDescriptor = fmt.Errorf("invalid file descriptor")
)
func (v *VirtualMachine) executeSyscall() {
syscallNumber := v.registers.Get(arch.SyscallRegister)
if !v.quiet {
log.Printf("Executing syscall number %d\n", syscallNumber)
}
switch syscallNumber {
case syscallRead:
v.syscallRead()
case syscallWrite:
v.syscallWrite()
default:
panic(fmt.Sprintf("invalid syscall number %d", syscallNumber))
}
}
// Available Syscalls:
// - read(int fileD, char *buf, size_t bytes)
// - write(int fileD, const char *buf, size_t bytes)
// syscallRead performs a generic read syscall
//
// Semantics: write(int fileD, const void *buf, size_t nBytes)
// fileD: register 1
// buf: register 2
// nBytes: register 3
//
// Reads the first nBytes from the file into buf.
func (v *VirtualMachine) syscallRead() {
fileD := int(v.registers.Get(1))
bufPtr := uint32(v.registers.Get(2))
nBytes := uint32(v.registers.Get(3))
err := v.syscallReadExecute(fileD, bufPtr, nBytes)
if err != nil {
if errors.Is(err, ErrInvalidFileDescriptor) {
v.setSyscallError(arch.ENO_BadFileDescriptor)
} else {
v.setSyscallError(arch.ENO_IO)
}
log.Printf("error: %v\n", err)
}
}
func (v *VirtualMachine) syscallReadExecute(fileD int, bufPtr uint32, nBytes uint32) error {
file, ok := v.fds[fileD]
if !ok {
return ErrInvalidFileDescriptor
}
buf := make([]byte, nBytes)
_, err := file.Read(buf)
if err != nil {
return err // todo: EOF
}
for i := uint32(0); i < nBytes; i++ {
v.memory.Write(bufPtr+i, 8, uint64(buf[i]))
}
return nil
}
// syscallWrite performs a generic write syscall
//
// Semantics: write(int fileD, const void *buf, size_t nBytes)
// fileD: register 1
// buf: register 2
// nBytes: register 3
//
// Writes the first nBytes bytes of buf to the file.
func (v *VirtualMachine) syscallWrite() {
fileD := int(v.registers.Get(1))
bufPtr := uint32(v.registers.Get(2))
nBytes := uint32(v.registers.Get(3))
err := v.syscallWriteExecute(fileD, bufPtr, nBytes)
if err != nil {
if errors.Is(err, ErrInvalidFileDescriptor) {
v.setSyscallError(arch.ENO_BadFileDescriptor)
} else {
v.setSyscallError(arch.ENO_IO)
}
log.Printf("error: %v\n", err)
}
}
func (v *VirtualMachine) syscallWriteExecute(fileD int, bufPtr uint32, nBytes uint32) error {
file, ok := v.fds[fileD]
if !ok {
return ErrInvalidFileDescriptor
}
for i := uint32(0); i < nBytes; i++ {
data := v.memory.Read(bufPtr, 8) // read single byte
singleByte := byte(data)
_, err := file.Write([]byte{singleByte})
if err != nil {
return fmt.Errorf("syscall write: %w", err)
}
bufPtr += 1
}
return nil
}
func (v *VirtualMachine) setSyscallError(eno uint64) {
v.registers.Set(arch.SyscallErrorRegister, eno)
}