[release-branch.go1.12] syscall: avoid _getdirentries64 on darwin

Getdirentries is implemented with the __getdirentries64 function
in libSystem.dylib. That function works, but it's on Apple's
can't-be-used-in-an-app-store-application list.

Implement Getdirentries using the underlying fdopendir/readdir_r/closedir.
The simulation isn't faithful, and could be slow, but it should handle
common cases.

Don't use Getdirentries in the stdlib, use fdopendir/readdir_r/closedir
instead (via (*os.File).readdirnames).

(Incorporates CL 170837 and CL 170698, which were small fixes to the
original tip CL.)

Fixes #31244

Update #28984

RELNOTE=yes

Change-Id: Ia6b5d003e5bfe43ba54b1e1d9cfa792cc6511717
Reviewed-on: https://go-review.googlesource.com/c/go/+/168479
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
(cherry picked from commit 9da6530)
Reviewed-on: https://go-review.googlesource.com/c/go/+/170640
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

Author: randall77

src/internal/poll/fd_opendir_ios.go renamed to src/internal/poll/fd_opendir_darwin.go

@@ -2,9 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin
-// +build arm arm64
-
 package poll
 
 import (

src/os/dir_ios.go renamed to src/os/dir_darwin.go

@@ -2,9 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin
-// +build arm arm64
-
 package os
 
 import (
@@ -47,12 +44,12 @@ func (f *File) readdirnames(n int) (names []string, err error) {
 
 	names = make([]string, 0, size)
 	var dirent syscall.Dirent
-	var entptr uintptr
-	for len(names) < size {
-		if res := readdir_r(d.dir, uintptr(unsafe.Pointer(&dirent)), uintptr(unsafe.Pointer(&entptr))); res != 0 {
+	var entptr *syscall.Dirent
+	for len(names) < size || n == -1 {
+		if res := readdir_r(d.dir, &dirent, &entptr); res != 0 {
 			return names, wrapSyscallError("readdir", syscall.Errno(res))
 		}
-		if entptr == 0 { // EOF
+		if entptr == nil { // EOF
 			break
 		}
 		if dirent.Ino == 0 {
@@ -84,4 +81,4 @@ func (f *File) readdirnames(n int) (names []string, err error) {
 func closedir(dir uintptr) (err error)
 
 //go:linkname readdir_r syscall.readdir_r
-func readdir_r(dir, entry, result uintptr) (res int)
+func readdir_r(dir uintptr, entry *syscall.Dirent, result **syscall.Dirent) (res int)

src/os/dir_unix.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.
 
-// +build aix darwin,!arm,!arm64 dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
+// +build aix dragonfly freebsd js,wasm linux nacl netbsd openbsd solaris
 
 package os
 

src/runtime/sys_darwin.go

@@ -89,6 +89,17 @@ func syscall_syscall6X(fn, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, err uintptr)
 }
 func syscall6X()
 
+//go:linkname syscall_syscallPtr syscall.syscallPtr
+//go:nosplit
+//go:cgo_unsafe_args
+func syscall_syscallPtr(fn, a1, a2, a3 uintptr) (r1, r2, err uintptr) {
+	entersyscallblock()
+	libcCall(unsafe.Pointer(funcPC(syscallPtr)), unsafe.Pointer(&fn))
+	exitsyscall()
+	return
+}
+func syscallPtr()
+
 //go:linkname syscall_rawSyscall syscall.rawSyscall
 //go:nosplit
 //go:cgo_unsafe_args

src/runtime/sys_darwin_32.go

@@ -19,14 +19,3 @@ func syscall_syscall9(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2, e
 	return
 }
 func syscall9()
-
-//go:linkname syscall_syscallPtr syscall.syscallPtr
-//go:nosplit
-//go:cgo_unsafe_args
-func syscall_syscallPtr(fn, a1, a2, a3 uintptr) (r1, r2, err uintptr) {
-	entersyscallblock()
-	libcCall(unsafe.Pointer(funcPC(syscallPtr)), unsafe.Pointer(&fn))
-	exitsyscall()
-	return
-}
-func syscallPtr()

src/runtime/sys_darwin_386.s

@@ -675,9 +675,42 @@ ok:
 	POPL	BP
 	RET
 
-// Not used on 386.
+// syscallPtr is like syscall except the libc function reports an
+// error by returning NULL and setting errno.
 TEXT runtime·syscallPtr(SB),NOSPLIT,$0
-	MOVL	$0xf1, 0xf1  // crash
+	PUSHL	BP
+	MOVL	SP, BP
+	SUBL	$24, SP
+	MOVL	32(SP), CX
+	MOVL	(0*4)(CX), AX // fn
+	MOVL	(1*4)(CX), DX // a1
+	MOVL	DX, 0(SP)
+	MOVL	(2*4)(CX), DX // a2
+	MOVL	DX, 4(SP)
+	MOVL	(3*4)(CX), DX // a3
+	MOVL	DX, 8(SP)
+
+	CALL	AX
+
+	MOVL	32(SP), CX
+	MOVL	AX, (4*4)(CX) // r1
+	MOVL	DX, (5*4)(CX) // r2
+
+	// syscallPtr libc functions return NULL on error
+	// and set errno.
+	TESTL	AX, AX
+	JNE	ok
+
+	// Get error code from libc.
+	CALL	libc_error(SB)
+	MOVL	(AX), AX
+	MOVL	32(SP), CX
+	MOVL	AX, (6*4)(CX) // err
+
+ok:
+	XORL	AX, AX        // no error (it's ignored anyway)
+	MOVL	BP, SP
+	POPL	BP
 	RET
 
 // syscall6 calls a function in libc on behalf of the syscall package.

src/runtime/sys_darwin_64.go

@@ -19,14 +19,3 @@ func syscall_syscallX(fn, a1, a2, a3 uintptr) (r1, r2, err uintptr) {
 	return
 }
 func syscallX()
-
-//go:linkname syscall_syscallXPtr syscall.syscallXPtr
-//go:nosplit
-//go:cgo_unsafe_args
-func syscall_syscallXPtr(fn, a1, a2, a3 uintptr) (r1, r2, err uintptr) {
-	entersyscallblock()
-	libcCall(unsafe.Pointer(funcPC(syscallXPtr)), unsafe.Pointer(&fn))
-	exitsyscall()
-	return
-}
-func syscallXPtr()

src/runtime/sys_darwin_amd64.s

@@ -637,9 +637,40 @@ ok:
 	POPQ	BP
 	RET
 
-// Not used on amd64.
-TEXT runtime·syscallXPtr(SB),NOSPLIT,$0
-	MOVL	$0xf1, 0xf1  // crash
+// syscallPtr is like syscallX except that the libc function reports an
+// error by returning NULL and setting errno.
+TEXT runtime·syscallPtr(SB),NOSPLIT,$0
+	PUSHQ	BP
+	MOVQ	SP, BP
+	SUBQ	$16, SP
+	MOVQ	(0*8)(DI), CX // fn
+	MOVQ	(2*8)(DI), SI // a2
+	MOVQ	(3*8)(DI), DX // a3
+	MOVQ	DI, (SP)
+	MOVQ	(1*8)(DI), DI // a1
+	XORL	AX, AX	      // vararg: say "no float args"
+
+	CALL	CX
+
+	MOVQ	(SP), DI
+	MOVQ	AX, (4*8)(DI) // r1
+	MOVQ	DX, (5*8)(DI) // r2
+
+	// syscallPtr libc functions return NULL on error
+	// and set errno.
+	TESTQ	AX, AX
+	JNE	ok
+
+	// Get error code from libc.
+	CALL	libc_error(SB)
+	MOVLQSX	(AX), AX
+	MOVQ	(SP), DI
+	MOVQ	AX, (6*8)(DI) // err
+
+ok:
+	XORL	AX, AX        // no error (it's ignored anyway)
+	MOVQ	BP, SP
+	POPQ	BP
 	RET
 
 // syscall6 calls a function in libc on behalf of the syscall package.

src/runtime/sys_darwin_arm.s

@@ -418,7 +418,7 @@ ok:
 	RET
 
 // syscallPtr is like syscall except the libc function reports an
-// error by returning NULL.
+// error by returning NULL and setting errno.
 TEXT runtime·syscallPtr(SB),NOSPLIT,$0
 	MOVW.W	R0, -4(R13)	// push structure pointer
 	MOVW	0(R0), R12	// fn

src/runtime/sys_darwin_arm64.s

@@ -465,9 +465,9 @@ TEXT runtime·syscallX(SB),NOSPLIT,$0
 ok:
 	RET
 
-// syscallXPtr is like syscallX except that the libc function reports an
-// error by returning NULL.
-TEXT runtime·syscallXPtr(SB),NOSPLIT,$0
+// syscallPtr is like syscallX except that the libc function reports an
+// error by returning NULL and setting errno.
+TEXT runtime·syscallPtr(SB),NOSPLIT,$0
 	SUB	$16, RSP	// push structure pointer
 	MOVD	R0, (RSP)