syscall: do not use NULL for zero-length read, write

Avoids problems running Linux binaries under QEMU.

R=r, gri
CC=golang-dev
https://golang.org/cl/4151043

src/pkg/syscall/mksyscall.sh

@@ -98,14 +98,11 @@ while(<>) {
 		} elsif($type =~ /^\[\](.*)/) {
 			# Convert slice into pointer, length.
 			# Have to be careful not to take address of &a[0] if len == 0:
-			# pass nil in that case.
+			# pass dummy pointer in that case.
+			# Used to pass nil, but some OSes or simulators reject write(fd, nil, 0).
 			$text .= "\tvar _p$n unsafe.Pointer\n";
 			$text .= "\tif len($name) > 0 {\n\t\t_p$n = unsafe.Pointer(\&${name}[0])\n\t}";
-			if($nacl) {
+			$text .= " else {\n\t\t_p$n = unsafe.Pointer(&_zero)\n\t}";
-				# NaCl rejects zero length write with nil pointer,
-				# so use non-nil pointer.
-				$text .= " else {\n\t\t_p$n = unsafe.Pointer(&_zero[0])\n\t}";
-			}
 			$text .= "\n";
 			push @args, "uintptr(_p$n)", "uintptr(len($name))";
 			$n++;

src/pkg/syscall/syscall.go

@@ -24,3 +24,7 @@ func StringByteSlice(s string) []byte {
 // StringBytePtr returns a pointer to a NUL-terminated array of bytes
 // containing the text of s.
 func StringBytePtr(s string) *byte { return &StringByteSlice(s)[0] }
+
+// Single-word zero for use when we need a valid pointer to 0 bytes.
+// See mksyscall.sh.
+var _zero uintptr

src/pkg/syscall/zsyscall_darwin_386.go

@@ -121,6 +121,8 @@ func recvfrom(fd int, p []byte, flags int, from *RawSockaddrAny, fromlen *_Sockl
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_RECVFROM, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(flags), uintptr(unsafe.Pointer(from)), uintptr(unsafe.Pointer(fromlen)))
 	n = int(r0)
@@ -134,6 +136,8 @@ func sendto(s int, buf []byte, flags int, to uintptr, addrlen _Socklen) (errno i
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS_SENDTO, uintptr(s), uintptr(_p0), uintptr(len(buf)), uintptr(flags), uintptr(to), uintptr(addrlen))
 	errno = int(e1)
@@ -155,6 +159,8 @@ func sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr)
 	var _p0 unsafe.Pointer
 	if len(mib) > 0 {
 		_p0 = unsafe.Pointer(&mib[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS___SYSCTL, uintptr(_p0), uintptr(len(mib)), uintptr(unsafe.Pointer(old)), uintptr(unsafe.Pointer(oldlen)), uintptr(unsafe.Pointer(new)), uintptr(newlen))
 	errno = int(e1)
@@ -377,6 +383,8 @@ func Getdirentries(fd int, buf []byte, basep *uintptr) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_GETDIRENTRIES64, uintptr(fd), uintptr(_p0), uintptr(len(buf)), uintptr(unsafe.Pointer(basep)), 0, 0)
 	n = int(r0)
@@ -414,6 +422,8 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETFSSTAT64, uintptr(_p0), uintptr(len(buf)), uintptr(flags))
 	n = int(r0)
@@ -601,6 +611,8 @@ func Pread(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PREAD, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), uintptr(offset>>32), 0)
 	n = int(r0)
@@ -614,6 +626,8 @@ func Pwrite(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PWRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), uintptr(offset>>32), 0)
 	n = int(r0)
@@ -627,6 +641,8 @@ func Read(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READ, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -640,6 +656,8 @@ func Readlink(path string, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READLINK, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -871,6 +889,8 @@ func Write(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_WRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)

src/pkg/syscall/zsyscall_darwin_amd64.go

@@ -121,6 +121,8 @@ func recvfrom(fd int, p []byte, flags int, from *RawSockaddrAny, fromlen *_Sockl
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_RECVFROM, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(flags), uintptr(unsafe.Pointer(from)), uintptr(unsafe.Pointer(fromlen)))
 	n = int(r0)
@@ -134,6 +136,8 @@ func sendto(s int, buf []byte, flags int, to uintptr, addrlen _Socklen) (errno i
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS_SENDTO, uintptr(s), uintptr(_p0), uintptr(len(buf)), uintptr(flags), uintptr(to), uintptr(addrlen))
 	errno = int(e1)
@@ -155,6 +159,8 @@ func sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr)
 	var _p0 unsafe.Pointer
 	if len(mib) > 0 {
 		_p0 = unsafe.Pointer(&mib[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS___SYSCTL, uintptr(_p0), uintptr(len(mib)), uintptr(unsafe.Pointer(old)), uintptr(unsafe.Pointer(oldlen)), uintptr(unsafe.Pointer(new)), uintptr(newlen))
 	errno = int(e1)
@@ -377,6 +383,8 @@ func Getdirentries(fd int, buf []byte, basep *uintptr) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_GETDIRENTRIES64, uintptr(fd), uintptr(_p0), uintptr(len(buf)), uintptr(unsafe.Pointer(basep)), 0, 0)
 	n = int(r0)
@@ -414,6 +422,8 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETFSSTAT64, uintptr(_p0), uintptr(len(buf)), uintptr(flags))
 	n = int(r0)
@@ -601,6 +611,8 @@ func Pread(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PREAD, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), 0, 0)
 	n = int(r0)
@@ -614,6 +626,8 @@ func Pwrite(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PWRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), 0, 0)
 	n = int(r0)
@@ -627,6 +641,8 @@ func Read(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READ, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -640,6 +656,8 @@ func Readlink(path string, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READLINK, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -871,6 +889,8 @@ func Write(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_WRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)

src/pkg/syscall/zsyscall_freebsd_386.go

@@ -121,6 +121,8 @@ func recvfrom(fd int, p []byte, flags int, from *RawSockaddrAny, fromlen *_Sockl
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_RECVFROM, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(flags), uintptr(unsafe.Pointer(from)), uintptr(unsafe.Pointer(fromlen)))
 	n = int(r0)
@@ -134,6 +136,8 @@ func sendto(s int, buf []byte, flags int, to uintptr, addrlen _Socklen) (errno i
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS_SENDTO, uintptr(s), uintptr(_p0), uintptr(len(buf)), uintptr(flags), uintptr(to), uintptr(addrlen))
 	errno = int(e1)
@@ -155,6 +159,8 @@ func sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr)
 	var _p0 unsafe.Pointer
 	if len(mib) > 0 {
 		_p0 = unsafe.Pointer(&mib[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS___SYSCTL, uintptr(_p0), uintptr(len(mib)), uintptr(unsafe.Pointer(old)), uintptr(unsafe.Pointer(oldlen)), uintptr(unsafe.Pointer(new)), uintptr(newlen))
 	errno = int(e1)
@@ -361,6 +367,8 @@ func Getdirentries(fd int, buf []byte, basep *uintptr) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_GETDIRENTRIES, uintptr(fd), uintptr(_p0), uintptr(len(buf)), uintptr(unsafe.Pointer(basep)), 0, 0)
 	n = int(r0)
@@ -398,6 +406,8 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETFSSTAT, uintptr(_p0), uintptr(len(buf)), uintptr(flags))
 	n = int(r0)
@@ -609,6 +619,8 @@ func Pread(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PREAD, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), uintptr(offset>>32), 0)
 	n = int(r0)
@@ -622,6 +634,8 @@ func Pwrite(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PWRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), uintptr(offset>>32), 0)
 	n = int(r0)
@@ -635,6 +649,8 @@ func Read(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READ, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -648,6 +664,8 @@ func Readlink(path string, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READLINK, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -871,6 +889,8 @@ func Write(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_WRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)

src/pkg/syscall/zsyscall_freebsd_amd64.go

@@ -121,6 +121,8 @@ func recvfrom(fd int, p []byte, flags int, from *RawSockaddrAny, fromlen *_Sockl
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_RECVFROM, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(flags), uintptr(unsafe.Pointer(from)), uintptr(unsafe.Pointer(fromlen)))
 	n = int(r0)
@@ -134,6 +136,8 @@ func sendto(s int, buf []byte, flags int, to uintptr, addrlen _Socklen) (errno i
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS_SENDTO, uintptr(s), uintptr(_p0), uintptr(len(buf)), uintptr(flags), uintptr(to), uintptr(addrlen))
 	errno = int(e1)
@@ -155,6 +159,8 @@ func sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr)
 	var _p0 unsafe.Pointer
 	if len(mib) > 0 {
 		_p0 = unsafe.Pointer(&mib[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS___SYSCTL, uintptr(_p0), uintptr(len(mib)), uintptr(unsafe.Pointer(old)), uintptr(unsafe.Pointer(oldlen)), uintptr(unsafe.Pointer(new)), uintptr(newlen))
 	errno = int(e1)
@@ -361,6 +367,8 @@ func Getdirentries(fd int, buf []byte, basep *uintptr) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_GETDIRENTRIES, uintptr(fd), uintptr(_p0), uintptr(len(buf)), uintptr(unsafe.Pointer(basep)), 0, 0)
 	n = int(r0)
@@ -398,6 +406,8 @@ func Getfsstat(buf []Statfs_t, flags int) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETFSSTAT, uintptr(_p0), uintptr(len(buf)), uintptr(flags))
 	n = int(r0)
@@ -609,6 +619,8 @@ func Pread(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PREAD, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), 0, 0)
 	n = int(r0)
@@ -622,6 +634,8 @@ func Pwrite(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PWRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), 0, 0)
 	n = int(r0)
@@ -635,6 +649,8 @@ func Read(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READ, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -648,6 +664,8 @@ func Readlink(path string, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READLINK, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -871,6 +889,8 @@ func Write(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_WRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)

src/pkg/syscall/zsyscall_linux_386.go

@@ -53,6 +53,8 @@ func Getcwd(buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETCWD, uintptr(_p0), uintptr(len(buf)), 0)
 	n = int(r0)
@@ -184,6 +186,8 @@ func EpollWait(epfd int, events []EpollEvent, msec int) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(events) > 0 {
 		_p0 = unsafe.Pointer(&events[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_EPOLL_WAIT, uintptr(epfd), uintptr(_p0), uintptr(len(events)), uintptr(msec), 0, 0)
 	n = int(r0)
@@ -277,6 +281,8 @@ func Getdents(fd int, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETDENTS64, uintptr(fd), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -391,6 +397,8 @@ func Klogctl(typ int, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_SYSLOG, uintptr(typ), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -468,6 +476,8 @@ func Read(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READ, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -481,6 +491,8 @@ func Readlink(path string, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READLINK, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -518,6 +530,8 @@ func Setdomainname(p []byte) (errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall(SYS_SETDOMAINNAME, uintptr(_p0), uintptr(len(p)), 0)
 	errno = int(e1)
@@ -530,6 +544,8 @@ func Sethostname(p []byte) (errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall(SYS_SETHOSTNAME, uintptr(_p0), uintptr(len(p)), 0)
 	errno = int(e1)
@@ -688,6 +704,8 @@ func Write(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_WRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -823,6 +841,8 @@ func Pread(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PREAD64, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), uintptr(offset>>32), 0)
 	n = int(r0)
@@ -836,6 +856,8 @@ func Pwrite(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PWRITE64, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), uintptr(offset>>32), 0)
 	n = int(r0)

src/pkg/syscall/zsyscall_linux_amd64.go

@@ -53,6 +53,8 @@ func Getcwd(buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETCWD, uintptr(_p0), uintptr(len(buf)), 0)
 	n = int(r0)
@@ -184,6 +186,8 @@ func EpollWait(epfd int, events []EpollEvent, msec int) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(events) > 0 {
 		_p0 = unsafe.Pointer(&events[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_EPOLL_WAIT, uintptr(epfd), uintptr(_p0), uintptr(len(events)), uintptr(msec), 0, 0)
 	n = int(r0)
@@ -277,6 +281,8 @@ func Getdents(fd int, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETDENTS64, uintptr(fd), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -391,6 +397,8 @@ func Klogctl(typ int, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_SYSLOG, uintptr(typ), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -468,6 +476,8 @@ func Read(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READ, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -481,6 +491,8 @@ func Readlink(path string, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READLINK, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -518,6 +530,8 @@ func Setdomainname(p []byte) (errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall(SYS_SETDOMAINNAME, uintptr(_p0), uintptr(len(p)), 0)
 	errno = int(e1)
@@ -530,6 +544,8 @@ func Sethostname(p []byte) (errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall(SYS_SETHOSTNAME, uintptr(_p0), uintptr(len(p)), 0)
 	errno = int(e1)
@@ -688,6 +704,8 @@ func Write(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_WRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -839,6 +857,8 @@ func Pread(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PREAD64, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), 0, 0)
 	n = int(r0)
@@ -852,6 +872,8 @@ func Pwrite(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_PWRITE64, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(offset), 0, 0)
 	n = int(r0)
@@ -1071,6 +1093,8 @@ func recvfrom(fd int, p []byte, flags int, from *RawSockaddrAny, fromlen *_Sockl
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_RECVFROM, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(flags), uintptr(unsafe.Pointer(from)), uintptr(unsafe.Pointer(fromlen)))
 	n = int(r0)
@@ -1084,6 +1108,8 @@ func sendto(s int, buf []byte, flags int, to uintptr, addrlen _Socklen) (errno i
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS_SENDTO, uintptr(s), uintptr(_p0), uintptr(len(buf)), uintptr(flags), uintptr(to), uintptr(addrlen))
 	errno = int(e1)

src/pkg/syscall/zsyscall_linux_arm.go

@@ -53,6 +53,8 @@ func Getcwd(buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETCWD, uintptr(_p0), uintptr(len(buf)), 0)
 	n = int(r0)
@@ -184,6 +186,8 @@ func EpollWait(epfd int, events []EpollEvent, msec int) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(events) > 0 {
 		_p0 = unsafe.Pointer(&events[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_EPOLL_WAIT, uintptr(epfd), uintptr(_p0), uintptr(len(events)), uintptr(msec), 0, 0)
 	n = int(r0)
@@ -277,6 +281,8 @@ func Getdents(fd int, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_GETDENTS64, uintptr(fd), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -391,6 +397,8 @@ func Klogctl(typ int, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_SYSLOG, uintptr(typ), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -468,6 +476,8 @@ func Read(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READ, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -481,6 +491,8 @@ func Readlink(path string, buf []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_READLINK, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(_p0), uintptr(len(buf)))
 	n = int(r0)
@@ -518,6 +530,8 @@ func Setdomainname(p []byte) (errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall(SYS_SETDOMAINNAME, uintptr(_p0), uintptr(len(p)), 0)
 	errno = int(e1)
@@ -530,6 +544,8 @@ func Sethostname(p []byte) (errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall(SYS_SETHOSTNAME, uintptr(_p0), uintptr(len(p)), 0)
 	errno = int(e1)
@@ -688,6 +704,8 @@ func Write(fd int, p []byte) (n int, errno int) {
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall(SYS_WRITE, uintptr(fd), uintptr(_p0), uintptr(len(p)))
 	n = int(r0)
@@ -802,6 +820,8 @@ func recvfrom(fd int, p []byte, flags int, from *RawSockaddrAny, fromlen *_Sockl
 	var _p0 unsafe.Pointer
 	if len(p) > 0 {
 		_p0 = unsafe.Pointer(&p[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	r0, _, e1 := Syscall6(SYS_RECVFROM, uintptr(fd), uintptr(_p0), uintptr(len(p)), uintptr(flags), uintptr(unsafe.Pointer(from)), uintptr(unsafe.Pointer(fromlen)))
 	n = int(r0)
@@ -815,6 +835,8 @@ func sendto(s int, buf []byte, flags int, to uintptr, addrlen _Socklen) (errno i
 	var _p0 unsafe.Pointer
 	if len(buf) > 0 {
 		_p0 = unsafe.Pointer(&buf[0])
+	} else {
+		_p0 = unsafe.Pointer(&_zero)
 	}
 	_, _, e1 := Syscall6(SYS_SENDTO, uintptr(s), uintptr(_p0), uintptr(len(buf)), uintptr(flags), uintptr(to), uintptr(addrlen))
 	errno = int(e1)