golang, call GetVolumeInformation winapi function

Question

Tries to call GetVolumeInformation function from golang. Want to get volume name.

Use spec's of api:

BOOL WINAPI GetVolumeInformation(
  _In_opt_  LPCTSTR lpRootPathName,
  _Out_opt_ LPTSTR  lpVolumeNameBuffer,
  _In_      DWORD   nVolumeNameSize,
  _Out_opt_ LPDWORD lpVolumeSerialNumber,
  _Out_opt_ LPDWORD lpMaximumComponentLength,
  _Out_opt_ LPDWORD lpFileSystemFlags,
  _Out_opt_ LPTSTR  lpFileSystemNameBuffer,
  _In_      DWORD   nFileSystemNameSize
);

Use code:

// test
package main

import (
    "fmt"
    "syscall"
    "unsafe"
)

func main() {
    var lpRootPathName = "C:\\"
    var lpVolumeNameBuffer string
    var nVolumeNameSize uint64
    var lpVolumeSerialNumber uint64
    var lpMaximumComponentLength uint64
    var lpFileSystemFlags uint64
    var lpFileSystemNameBuffer string
    var nFileSystemNameSize uint32

    kernel32, _ := syscall.LoadLibrary("kernel32.dll")
    getVolume, _ := syscall.GetProcAddress(kernel32, "GetVolumeInformationW")

    var nargs uintptr = 8
    ret, _, callErr := syscall.Syscall9(uintptr(getVolume),
        nargs,
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(lpRootPathName))),
        uintptr(unsafe.Pointer(&lpVolumeNameBuffer)),
        uintptr(unsafe.Pointer(&nVolumeNameSize)),
        uintptr(unsafe.Pointer(&lpVolumeSerialNumber)),
        uintptr(unsafe.Pointer(&lpMaximumComponentLength)),
        uintptr(unsafe.Pointer(&lpFileSystemFlags)),
        uintptr(unsafe.Pointer(&lpFileSystemNameBuffer)),
        uintptr(unsafe.Pointer(&nFileSystemNameSize)),
        0)
    fmt.Println(ret, callErr, lpVolumeNameBuffer)
}

... and finally have error :(

unexpected fault address 0xffffffffffffffff
fatal error: fault
[signal 0xc0000005 code=0x0 addr=0xffffffffffffffff pc=0x456b11]

Don't understand and google cant'd help with calling winapi functions and returng string as result.

Thank's.

Answer 1

Package unsafe

Package unsafe contains operations that step around the type safety of Go programs.

type Pointer

type Pointer *ArbitraryType

Pointer represents a pointer to an arbitrary type. There are four special operations available for type Pointer that are not available for other types.

1) A pointer value of any type can be converted to a Pointer.

2) A Pointer can be converted to a pointer value of any type.

3) A uintptr can be converted to a Pointer.

4) A Pointer can be converted to a uintptr.

Pointer therefore allows a program to defeat the type system and read and write arbitrary memory. It should be used with extreme care.

You failed to heed the warning that unsafe.Pointer "should be used with extreme care."

Try this:

package main

import (
    "fmt"
    "syscall"
    "unsafe"
)

func main() {
    var RootPathName = `C:\`
    var VolumeNameBuffer = make([]uint16, syscall.MAX_PATH+1)
    var nVolumeNameSize = uint32(len(VolumeNameBuffer))
    var VolumeSerialNumber uint32
    var MaximumComponentLength uint32
    var FileSystemFlags uint32
    var FileSystemNameBuffer = make([]uint16, 255)
    var nFileSystemNameSize uint32 = syscall.MAX_PATH + 1

    kernel32, _ := syscall.LoadLibrary("kernel32.dll")
    getVolume, _ := syscall.GetProcAddress(kernel32, "GetVolumeInformationW")

    var nargs uintptr = 8
    ret, _, callErr := syscall.Syscall9(uintptr(getVolume),
        nargs,
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(RootPathName))),
        uintptr(unsafe.Pointer(&VolumeNameBuffer[0])),
        uintptr(nVolumeNameSize),
        uintptr(unsafe.Pointer(&VolumeSerialNumber)),
        uintptr(unsafe.Pointer(&MaximumComponentLength)),
        uintptr(unsafe.Pointer(&FileSystemFlags)),
        uintptr(unsafe.Pointer(&FileSystemNameBuffer[0])),
        uintptr(nFileSystemNameSize),
        0)
    fmt.Println(ret, callErr, syscall.UTF16ToString(VolumeNameBuffer))
}