在 Golang 的 syscall 包中，syscall.Syscall() 是如何以及在何处为特定于 Windows 的系统调用定义的？

Question

I'm trying to understand some of the low-level details of Golangs syscall package. In particular, I'm interested in Windows-specific system calls (see the example below).

I can find the definition of syscall.Syscall() for UNIX-based systems:

• https://golang.org/src/syscall/syscall_unix.go?s=496:562#L18
• https://golang.org/src/syscall/asm_unix_amd64.s

However, I cannot find any such definition for Windows-based systems, like an asm_windows_amd64.s .

In particular, asm_unix_amd64.s has the following build directive, so its ·Syscall(SB),NOSPLIT,$0-56 definition cannot be the one also called for Windows system calls:

 1// +build netbsd freebsd openbsd dragonfly

Where is syscall.Syscall() defined for Windows-based systems?

Example: https://godoc.org/golang.org/x/sys/windows#example-LoadLibrary

h, err := windows.LoadLibrary("kernel32.dll")
if err != nil {
    abort("LoadLibrary", err)
}
defer windows.FreeLibrary(h)
proc, err := windows.GetProcAddress(h, "GetVersion")
if err != nil {
    abort("GetProcAddress", err)
}
r, _, _ := syscall.Syscall(uintptr(proc), 0, 0, 0, 0)
major := byte(r)
minor := uint8(r >> 8)
build := uint16(r >> 16)
print("windows version ", major, ".", minor, " (Build ", build, ")\n")

Answer 1

I don't have or use Windows, but some grep work with the source finds this:

• syscall.Syscall , syscall.Syscall6 , and so on are defined in runtime/syscall_windows.go . For instance, starting at line 179 (currently):

   //go:linkname syscall_Syscall syscall.Syscall //go:nosplit func syscall_Syscall(fn, nargs, a1, a2, a3 uintptr) (r1, r2, err uintptr) { lockOSThread() defer unlockOSThread() c := &getg().m.syscall c.fn = fn cn = nargs c.args = uintptr(noescape(unsafe.Pointer(&a1))) cgocall(asmstdcallAddr, unsafe.Pointer(c)) return c.r1, c.r2, c.err

  }

  The go:linkname is the magic that makes this function be named syscall.Syscall , even though it's named runtime.syscall_Syscall here.

• These use DLLs loaded earlier to figure out how to really make the system calls. (This is what c.fn is about.) To call into the DLLs, the Go runtime must lock the thread (see the first two calls) and use cgocall to invoke the DLL. Furthermore, special trickery is required to pass the parameters using the structure obtained by getc().m.syscall .

• Startup loading appears to happen via runtime/os_windows.go . Note that _GetProcAddress (and other functions) are filled-in by the Windows loader, which allows bootstrapping.