undo CL 45930043 / c22889382a17

The compiler change is an ugly hack.
We can do better.

««« original CL description
syscall: mark arguments to Syscall as noescape
Heap arguments to "async" syscalls will break when/if we have moving GC anyway.
With this change is must not break until moving GC, because a user must
reference the object in Go to preserve liveness. Otherwise the code is broken already.
Reduces number of leaked params from 125 to 36 on linux.

R=golang-codereviews, mikioh.mikioh, bradfitz
CC=cshapiro, golang-codereviews, khr, rsc
https://golang.org/cl/45930043
»»»

R=golang-codereviews, r
CC=bradfitz, dvyukov, golang-codereviews
https://golang.org/cl/53870043

src/cmd/gc/esc.c

@@ -1135,13 +1135,8 @@ esctag(EscState *e, Node *func)
 	if(func->nbody == nil) {
 		if(func->noescape) {
 			for(t=getinargx(func->type)->type; t; t=t->down)
-				// Mark all arguments, not only pointers,
-				// to support the following use case.
-				// Syscall package converts all pointers to uintptr
-				// when calls asm-implemented Syscall function:
-				// 
-				//   Syscall(SYS_FOO, uintptr(unsafe.Pointer(p)), 0, 0)
-				t->note = mktag(EscNone);
+				if(haspointers(t->type))
+					t->note = mktag(EscNone);
 		}
 		return;
 	}

src/pkg/syscall/dll_windows.go

@@ -20,31 +20,11 @@ type DLLError struct {
 func (e *DLLError) Error() string { return e.Msg }
 
 // Implemented in ../runtime/syscall_windows.goc.
-
-// Pointers passed to syscalls must not escape (be accessed by OS after the syscall returns).
-// For heap objects this will break when/if we have moving GC.
-// And for other objects (global, C allocated) go:noescape has no effect.
-
-//go:noescape
-
 func Syscall(trap, nargs, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
-
-//go:noescape
-
 func Syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
-
-//go:noescape
-
 func Syscall9(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno)
-
-//go:noescape
-
 func Syscall12(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12 uintptr) (r1, r2 uintptr, err Errno)
-
-//go:noescape
-
 func Syscall15(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15 uintptr) (r1, r2 uintptr, err Errno)
-
 func loadlibrary(filename *uint16) (handle uintptr, err Errno)
 func getprocaddress(handle uintptr, procname *uint8) (proc uintptr, err Errno)
 

src/pkg/syscall/syscall_linux_386.go

@@ -169,16 +169,7 @@ const (
 	_SENDMMSG    = 20
 )
 
-// Pointers passed to syscalls must not escape (be accessed by OS after the syscall returns).
-// For heap objects this will break when/if we have moving GC.
-// And for other objects (global, C allocated) go:noescape has no effect.
-
-//go:noescape
-
 func socketcall(call int, a0, a1, a2, a3, a4, a5 uintptr) (n int, err Errno)
-
-//go:noescape
-
 func rawsocketcall(call int, a0, a1, a2, a3, a4, a5 uintptr) (n int, err Errno)
 
 func accept(s int, rsa *RawSockaddrAny, addrlen *_Socklen) (fd int, err error) {

src/pkg/syscall/syscall_plan9.go

@@ -51,24 +51,9 @@ var (
 // creation of IPv6 sockets to return EAFNOSUPPORT.
 var SocketDisableIPv6 bool
 
-// Pointers passed to syscalls must not escape (be accessed by OS after the syscall returns).
-// For heap objects this will break when/if we have moving GC.
-// And for other objects (global, C allocated) go:noescape has no effect.
-
-//go:noescape
-
 func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err ErrorString)
-
-//go:noescape
-
 func Syscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err ErrorString)
-
-//go:noescape
-
 func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2, err uintptr)
-
-//go:noescape
-
 func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr)
 
 func atoi(b []byte) (n uint) {

src/pkg/syscall/syscall_unix.go

@@ -23,24 +23,9 @@ const (
 	netbsd32Bit = runtime.GOOS == "netbsd" && sizeofPtr == 4
 )
 
-// Pointers passed to syscalls must not escape (be accessed by OS after the syscall returns).
-// For heap objects this will break when/if we have moving GC.
-// And for other objects (global, C allocated) go:noescape has no effect.
-
-//go:noescape
-
 func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
-
-//go:noescape
-
 func Syscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
-
-//go:noescape
-
 func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
-
-//go:noescape
-
 func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
 
 // Mmap manager, for use by operating system-specific implementations.