Hi,
I'm a bit confused as to how the golang.org/x/sys package works.
>From the documentation of unsafe.Pointer:
>(4) Conversion of a Pointer to a uintptr when calling syscall.Syscall.
> The Syscall functions in package syscall pass their uintptr arguments
> directly to the operating system, which then may, depending on the details
> of the call, reinterpret some of them as pointers.
> That is, the system call implementation is implicitly converting certain
> arguments back from uintptr to pointer.
> If a pointer argument must be converted to uintptr for use as an argument,
> that conversion must appear in the call expression itself
Now, as far as I can tell this forces non stdlib packages to adhere to exactly
that.
As far as I can tell x/sys is just a common namespace for the go authors, but
as far as the compiler itself is concerned, that's a normal module not the
stdlib.
Or is this a wrong assumption?
Reason I ask is because the code in x/sys clearly violates that rule.
in unix/ioctl.go there's
```
// IoctlSetPointerInt performs an ioctl operation which sets an
// integer value on fd, using the specified request number. The ioctl
// argument is called with a pointer to the integer value, rather than
// passing the integer value directly.
func IoctlSetPointerInt(fd int, req uint, value int) error {
v := int32(value)
return ioctl(fd, req, uintptr(unsafe.Pointer(&v)))
}
```
and the declaration of ioctl in zsyskall_linux.go:
```
func ioctl(fd int, req uint, arg uintptr) (err error) {
_, _, e1 := Syscall(SYS_IOCTL, uintptr(fd), uintptr(req), uintptr(arg))
if e1 != 0 {
err = errnoErr(e1)
}
return
}
```
Now, for starters ioctl includes a pointless conversion of a uintptr to a
uintptr,
for the arg parameter can anyone tell me why?
Second (and this is my actual question), isn't that in violation of the unsafe
constraints cited above?
IoctlSetPointerInt clearly converts a unsafe.Pointer to a uintptr and *doesn't*
directly call syscall.Syscall.
Why is this valid?
Thanks in advance.
Regards,
Reto
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