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).

Fixes #30933

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>

7 files changed, 84 insertions, 31 deletions

diff --git a/src/runtime/sys_darwin.go b/src/runtime/sys_darwin.go
index f34ac88352..434fa5f588 100644
--- a/src/runtime/sys_darwin.go
+++ b/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
diff --git a/src/runtime/sys_darwin_32.go b/src/runtime/sys_darwin_32.go
index 2f17091327..f126be83e5 100644
--- a/src/runtime/sys_darwin_32.go
+++ b/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()
diff --git a/src/runtime/sys_darwin_386.s b/src/runtime/sys_darwin_386.s
index 1bc1a63c28..d318509e0a 100644
--- a/src/runtime/sys_darwin_386.s
+++ b/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.
diff --git a/src/runtime/sys_darwin_64.go b/src/runtime/sys_darwin_64.go
index 8c128811b9..07b0bb54af 100644
--- a/src/runtime/sys_darwin_64.go
+++ b/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()
diff --git a/src/runtime/sys_darwin_amd64.s b/src/runtime/sys_darwin_amd64.s
index f99cb00ab8..934c510b88 100644
--- a/src/runtime/sys_darwin_amd64.s
+++ b/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.
diff --git a/src/runtime/sys_darwin_arm.s b/src/runtime/sys_darwin_arm.s
index 54c7afbf34..6c3fa0739d 100644
--- a/src/runtime/sys_darwin_arm.s
+++ b/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
diff --git a/src/runtime/sys_darwin_arm64.s b/src/runtime/sys_darwin_arm64.s
index 29951d8ad7..89a2b8a054 100644
--- a/src/runtime/sys_darwin_arm64.s
+++ b/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)