runtime: revert use of __fork to work around Apple atfork bugs

An Apple engineer suggests that since __fork is not public API,
it would be better to use a different fix. With the benefit of source code,
they suggest using xpc_date_create_from_current instead of
xpc_atfork_child. The latter sets some flags that disable certain
functionality for the remainder of the process lifetime (expecting exec),
while the former should do the necessary setup.

Reverting the __fork fix in order to prepare a clean fix based
on CL 451735 using xpc_date_create_from_current.

This reverts commit c61d322d5f.

Change-Id: I2da293ff537237ffd2d40ad756d827c95c84635b
Reviewed-on: https://go-review.googlesource.com/c/go/+/460475
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/syscall/exec_libc2.go

@@ -78,7 +78,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	// About to call fork.
 	// No more allocation or calls of non-assembly functions.
 	runtime_BeforeFork()
-	r1, _, err1 = rawSyscall(forkTrampoline, 0, 0, 0)
+	r1, _, err1 = rawSyscall(abi.FuncPCABI0(libc_fork_trampoline), 0, 0, 0)
 	if err1 != 0 {
 		runtime_AfterFork()
 		return 0, err1
@@ -276,6 +276,6 @@ childerror:
 	// send error code on pipe
 	rawSyscall(abi.FuncPCABI0(libc_write_trampoline), uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
 	for {
-		rawSyscall(exitTrampoline, 253, 0, 0)
+		rawSyscall(abi.FuncPCABI0(libc_exit_trampoline), 253, 0, 0)
 	}
 }

src/syscall/syscall_darwin.go

@@ -22,34 +22,7 @@ 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)
 
-// These are called from exec_libc2.go in the child of fork.
+var dupTrampoline = abi.FuncPCABI0(libc_dup2_trampoline)
-// The names differ between macOS and OpenBSD, so we need
-// to declare the specific ones used here to keep the exec_libc2.go
-// code portable.
-//
-// We use __fork and __exit, not fork and exit, to avoid the libc atfork
-// and atexit handlers. The atfork handlers have caused fork child
-// hangs in the past (see #33565, #56784). The atexit handlers have
-// not, but the non-libc ports all invoke the system call, so doing
-// the same here makes sense. In general we wouldn't expect
-// atexit handlers to work terribly well in a fork child anyway.
-// (Also, perhaps the atfork handlers clear the atexit handlers,
-// in which case we definitely need to avoid calling the libc exit
-// if we bypass the libc fork.)
-//
-// Other calls that are made in the child after the fork are
-// ptrace, setsid, setpgid, getpid, ioctl, chroot, setgroups,
-// setgid, setuid, chdir, dup2, fcntl, close, execve, and write.
-// Those are all simple kernel wrappers that should be safe
-// to be called directly. The fcntl and ioctl functions do run
-// some code around the kernel call, but they don't call any
-// other functions, so for now we keep using them instead of
-// calling the lower-level __fcntl and __ioctl functions.
-var (
-	dupTrampoline  = abi.FuncPCABI0(libc_dup2_trampoline)
-	exitTrampoline = abi.FuncPCABI0(libc___exit_trampoline)
-	forkTrampoline = abi.FuncPCABI0(libc___fork_trampoline)
-)
 
 type SockaddrDatalink struct {
 	Len    uint8
@@ -237,12 +210,11 @@ func Kill(pid int, signum Signal) (err error) { return kill(pid, int(signum), 1)
 //sys	writev(fd int, iovecs []Iovec) (cnt uintptr, err error)
 //sys   mmap(addr uintptr, length uintptr, prot int, flag int, fd int, pos int64) (ret uintptr, err error)
 //sys   munmap(addr uintptr, length uintptr) (err error)
-//sysnb __fork() (pid int, err error)
+//sysnb fork() (pid int, err error)
 //sysnb ioctl(fd int, req int, arg int) (err error)
 //sysnb ioctlPtr(fd int, req uint, arg unsafe.Pointer) (err error) = SYS_ioctl
 //sysnb execve(path *byte, argv **byte, envp **byte) (err error)
 //sysnb exit(res int) (err error)
-//sysnb __exit(res int) (err error)
 //sys	sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr) (err error)
 //sys	fcntlPtr(fd int, cmd int, arg unsafe.Pointer) (val int, err error) = SYS_fcntl
 //sys   unlinkat(fd int, path string, flags int) (err error)

src/syscall/syscall_openbsd_libc.go

@@ -10,11 +10,7 @@ import (
 	"internal/abi"
 )
 
-var (
+var dupTrampoline = abi.FuncPCABI0(libc_dup3_trampoline)
-	dupTrampoline  = abi.FuncPCABI0(libc_dup3_trampoline)
-	exitTrampoline = abi.FuncPCABI0(libc_exit_trampoline)
-	forkTrampoline = abi.FuncPCABI0(libc_fork_trampoline)
-)
 
 func init() {
 	execveOpenBSD = execve

src/syscall/zsyscall_darwin_amd64.go

@@ -1734,8 +1734,8 @@ func libc_munmap_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func __fork() (pid int, err error) {
+func fork() (pid int, err error) {
-	r0, _, e1 := rawSyscall(abi.FuncPCABI0(libc___fork_trampoline), 0, 0, 0)
+	r0, _, e1 := rawSyscall(abi.FuncPCABI0(libc_fork_trampoline), 0, 0, 0)
 	pid = int(r0)
 	if e1 != 0 {
 		err = errnoErr(e1)
@@ -1743,9 +1743,9 @@ func __fork() (pid int, err error) {
 	return
 }
 
-func libc___fork_trampoline()
+func libc_fork_trampoline()
 
-//go:cgo_import_dynamic libc___fork __fork "/usr/lib/libSystem.B.dylib"
+//go:cgo_import_dynamic libc_fork fork "/usr/lib/libSystem.B.dylib"
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
@@ -1801,20 +1801,6 @@ func libc_exit_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func __exit(res int) (err error) {
-	_, _, e1 := rawSyscall(abi.FuncPCABI0(libc___exit_trampoline), uintptr(res), 0, 0)
-	if e1 != 0 {
-		err = errnoErr(e1)
-	}
-	return
-}
-
-func libc___exit_trampoline()
-
-//go:cgo_import_dynamic libc___exit __exit "/usr/lib/libSystem.B.dylib"
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr) (err error) {
 	var _p0 unsafe.Pointer
 	if len(mib) > 0 {

src/syscall/zsyscall_darwin_amd64.s

@@ -221,16 +221,14 @@ TEXT ·libc_mmap_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_mmap(SB)
 TEXT ·libc_munmap_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_munmap(SB)
-TEXT ·libc___fork_trampoline(SB),NOSPLIT,$0-0
+TEXT ·libc_fork_trampoline(SB),NOSPLIT,$0-0
-	JMP	libc___fork(SB)
+	JMP	libc_fork(SB)
 TEXT ·libc_ioctl_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_ioctl(SB)
 TEXT ·libc_execve_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_execve(SB)
 TEXT ·libc_exit_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_exit(SB)
-TEXT ·libc___exit_trampoline(SB),NOSPLIT,$0-0
-	JMP	libc___exit(SB)
 TEXT ·libc_sysctl_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_sysctl(SB)
 TEXT ·libc_unlinkat_trampoline(SB),NOSPLIT,$0-0

src/syscall/zsyscall_darwin_arm64.go

@@ -1734,8 +1734,8 @@ func libc_munmap_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func __fork() (pid int, err error) {
+func fork() (pid int, err error) {
-	r0, _, e1 := rawSyscall(abi.FuncPCABI0(libc___fork_trampoline), 0, 0, 0)
+	r0, _, e1 := rawSyscall(abi.FuncPCABI0(libc_fork_trampoline), 0, 0, 0)
 	pid = int(r0)
 	if e1 != 0 {
 		err = errnoErr(e1)
@@ -1743,9 +1743,9 @@ func __fork() (pid int, err error) {
 	return
 }
 
-func libc___fork_trampoline()
+func libc_fork_trampoline()
 
-//go:cgo_import_dynamic libc___fork __fork "/usr/lib/libSystem.B.dylib"
+//go:cgo_import_dynamic libc_fork fork "/usr/lib/libSystem.B.dylib"
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
@@ -1801,20 +1801,6 @@ func libc_exit_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func __exit(res int) (err error) {
-	_, _, e1 := rawSyscall(abi.FuncPCABI0(libc___exit_trampoline), uintptr(res), 0, 0)
-	if e1 != 0 {
-		err = errnoErr(e1)
-	}
-	return
-}
-
-func libc___exit_trampoline()
-
-//go:cgo_import_dynamic libc___exit __exit "/usr/lib/libSystem.B.dylib"
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr) (err error) {
 	var _p0 unsafe.Pointer
 	if len(mib) > 0 {

src/syscall/zsyscall_darwin_arm64.s

@@ -221,16 +221,14 @@ TEXT ·libc_mmap_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_mmap(SB)
 TEXT ·libc_munmap_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_munmap(SB)
-TEXT ·libc___fork_trampoline(SB),NOSPLIT,$0-0
+TEXT ·libc_fork_trampoline(SB),NOSPLIT,$0-0
-	JMP	libc___fork(SB)
+	JMP	libc_fork(SB)
 TEXT ·libc_ioctl_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_ioctl(SB)
 TEXT ·libc_execve_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_execve(SB)
 TEXT ·libc_exit_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_exit(SB)
-TEXT ·libc___exit_trampoline(SB),NOSPLIT,$0-0
-	JMP	libc___exit(SB)
 TEXT ·libc_sysctl_trampoline(SB),NOSPLIT,$0-0
 	JMP	libc_sysctl(SB)
 TEXT ·libc_unlinkat_trampoline(SB),NOSPLIT,$0-0