syscall: use fcntl F_DUP2FD_CLOEXEC in forkAndExecInChild on solaris

Use fcntl(oldfd, F_DUP2FD_CLOEXEC, newfd) to duplicate the file
descriptor and mark is as close-on-exec instead of dup2 & fcntl.

Note that the value for F_DUP2FD_CLOEXEC is different on Solaris and
Illumos and thus the definition is moved from zerrors_solaris_amd64.go
to solaris/illumos specific files.

Change-Id: I9a52801d1a01471ec3f065520575e3fafee92855
Reviewed-on: https://go-review.googlesource.com/c/go/+/428375
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Auto-Submit: Jenny Rakoczy <jenny@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Jenny Rakoczy <jenny@golang.org>
Run-TryBot: Jenny Rakoczy <jenny@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>

src/syscall/exec_libc.go

@@ -199,7 +199,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	// so that pass 2 won't stomp on an fd it needs later.
 	if pipe < nextfd {
 		switch runtime.GOOS {
-		case "illumos":
+		case "illumos", "solaris":
 			_, err1 = fcntl1(uintptr(pipe), _F_DUP2FD_CLOEXEC, uintptr(nextfd))
 		default:
 			_, err1 = dup2child(uintptr(pipe), uintptr(nextfd))
@@ -220,7 +220,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 				nextfd++
 			}
 			switch runtime.GOOS {
-			case "illumos":
+			case "illumos", "solaris":
 				_, err1 = fcntl1(uintptr(fd[i]), _F_DUP2FD_CLOEXEC, uintptr(nextfd))
 			default:
 				_, err1 = dup2child(uintptr(fd[i]), uintptr(nextfd))

src/syscall/syscall_illumos.go

@@ -4,12 +4,13 @@
 
 //go:build illumos
 
-// Illumos system calls not present on Solaris.
-
 package syscall
 
 import "unsafe"
 
+// F_DUP2FD_CLOEXEC has different values on Solaris and Illumos.
+const F_DUP2FD_CLOEXEC = 0x24
+
 //go:cgo_import_dynamic libc_flock flock "libc.so"
 
 //go:linkname procFlock libc_flock

src/syscall/syscall_solaris.go

@@ -14,13 +14,13 @@ package syscall
 
 import "unsafe"
 
+const _F_DUP2FD_CLOEXEC = F_DUP2FD_CLOEXEC
+
 func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
 func Syscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
 func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
 func RawSyscall6(trap, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
 
-const _F_DUP2FD_CLOEXEC = F_DUP2FD_CLOEXEC
-
 // Implemented in asm_solaris_amd64.s.
 func rawSysvicall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
 func sysvicall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)

src/syscall/syscall_solarisonly.go

@@ -0,0 +1,10 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build solaris && !illumos
+
+package syscall
+
+// F_DUP2FD_CLOEXEC has different values on Solaris and Illumos.
+const F_DUP2FD_CLOEXEC = 0x30

src/syscall/zerrors_solaris_amd64.go

@@ -276,7 +276,6 @@ const (
 	F_CHKFL                       = 0x8
 	F_COMPAT                      = 0x8
 	F_DUP2FD                      = 0x9
-	F_DUP2FD_CLOEXEC              = 0x24
 	F_DUPFD                       = 0x0
 	F_DUPFD_CLOEXEC               = 0x25
 	F_FREESP                      = 0xb