cmd/link/internal/ld, internal/syscall/unix: use posix_fallocate on netbsd

The posix_fallocate system call is available since NetBSD 7.0, see
https://man.netbsd.org/posix_fallocate.2

Re-use the syscall wrappers already in place for freebsd. Note that
posix_fallocate on netbsd also returns the result in r1 rather than in
errno:

> If successful, posix_fallocate() returns zero. It returns an error on failure, without
> setting errno.

Source: https://man.netbsd.org/posix_fallocate.2#RETURN%20VALUES

Cq-Include-Trybots: luci.golang.try:gotip-netbsd-arm64
Change-Id: Iaa1f6a805d511645da7f1d2737235bfd42da3407
Reviewed-on: https://go-review.googlesource.com/c/go/+/480475
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/link/internal/ld/fallocate_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build darwin || (freebsd && go1.21) || linux
+//go:build darwin || (freebsd && go1.21) || linux || (netbsd && go1.25)
 
 package ld
 

src/cmd/link/internal/ld/outbuf_bsd.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build freebsd && go1.21
+//go:build (freebsd && go1.21) || (netbsd && go1.25)
 
 package ld
 

src/cmd/link/internal/ld/outbuf_mmap.go

@@ -28,7 +28,7 @@ func (out *OutBuf) Mmap(filesize uint64) (err error) {
 		// Some file systems do not support fallocate. We ignore that error as linking
 		// can still take place, but you might SIGBUS when you write to the mmapped
 		// area.
-		if err != syscall.ENOTSUP && err != syscall.EPERM && err != errNoFallocate {
+		if err != syscall.ENOTSUP && err != syscall.EOPNOTSUPP && err != syscall.EPERM && err != errNoFallocate {
 			return err
 		}
 	}

src/cmd/link/internal/ld/outbuf_nofallocate.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !darwin && !(freebsd && go1.21) && !linux
+//go:build !darwin && !(freebsd && go1.21) && !linux && !(netbsd && go1.25)
 
 package ld
 

src/internal/syscall/unix/at_sysnum_netbsd.go

@@ -17,6 +17,7 @@ const (
 	renameatTrap       uintptr = syscall.SYS_RENAMEAT
 	linkatTrap         uintptr = syscall.SYS_LINKAT
 	symlinkatTrap      uintptr = syscall.SYS_SYMLINKAT
+	posixFallocateTrap uintptr = 479
 )
 
 const (

src/internal/syscall/unix/fallocate_bsd_386.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build (freebsd || netbsd) && 386
+
 package unix
 
 import "syscall"
@@ -9,6 +11,7 @@ import "syscall"
 func PosixFallocate(fd int, off int64, size int64) error {
 	// If successful, posix_fallocate() returns zero. It returns an error on failure, without
 	// setting errno. See https://man.freebsd.org/cgi/man.cgi?query=posix_fallocate&sektion=2&n=1
+	// and https://man.netbsd.org/posix_fallocate.2#RETURN%20VALUES
 	r1, _, _ := syscall.Syscall6(posixFallocateTrap, uintptr(fd), uintptr(off), uintptr(off>>32), uintptr(size), uintptr(size>>32), 0)
 	if r1 != 0 {
 		return syscall.Errno(r1)

src/internal/syscall/unix/fallocate_bsd_64bit.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build freebsd && (amd64 || arm64 || riscv64)
+//go:build (freebsd || netbsd) && (amd64 || arm64 || riscv64)
 
 package unix
 
@@ -11,6 +11,7 @@ import "syscall"
 func PosixFallocate(fd int, off int64, size int64) error {
 	// If successful, posix_fallocate() returns zero. It returns an error on failure, without
 	// setting errno. See https://man.freebsd.org/cgi/man.cgi?query=posix_fallocate&sektion=2&n=1
+	// and https://man.netbsd.org/posix_fallocate.2#RETURN%20VALUES
 	r1, _, _ := syscall.Syscall(posixFallocateTrap, uintptr(fd), uintptr(off), uintptr(size))
 	if r1 != 0 {
 		return syscall.Errno(r1)

src/internal/syscall/unix/fallocate_bsd_arm.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build (freebsd || netbsd) && arm
+
 package unix
 
 import "syscall"
@@ -9,6 +11,7 @@ import "syscall"
 func PosixFallocate(fd int, off int64, size int64) error {
 	// If successful, posix_fallocate() returns zero. It returns an error on failure, without
 	// setting errno. See https://man.freebsd.org/cgi/man.cgi?query=posix_fallocate&sektion=2&n=1
+	// and https://man.netbsd.org/posix_fallocate.2#RETURN%20VALUES
 	//
 	// The padding 0 argument is needed because the ARM calling convention requires that if an
 	// argument (off in this case) needs double-word alignment (8-byte), the NCRN (next core