[release-branch.go1.18] runtime: revert "call __fork instead of fork on darwin"

A recent comment on #57263 reports an unexplained crash in a cgo program
that is fixed by reverting the __fork fix. We don't have any viable fix for the
os/exec bug at this point, so give up on a fix for the January point releases.

This reverts CL 459179 (commit 07b6ffb79c90).

Fixes #57689.

Change-Id: I3b81de6bded399f47862325129e86a65c83d8e3b
Reviewed-on: https://go-review.googlesource.com/c/go/+/461116
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

7 files changed, 15 insertions, 81 deletions

diff --git a/src/syscall/exec_libc2.go b/src/syscall/exec_libc2.go
index bd2ce6820de..b05f053bbf3 100644
--- a/src/syscall/exec_libc2.go
+++ b/src/syscall/exec_libc2.go
@@ -76,7 +76,7 @@ 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
@@ -260,6 +260,6 @@ 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)
 	}
 }
diff --git a/src/syscall/syscall_darwin.go b/src/syscall/syscall_darwin.go
index 346e6862cd8..902d6e77e11 100644
--- a/src/syscall/syscall_darwin.go
+++ b/src/syscall/syscall_darwin.go
@@ -17,34 +17,6 @@ import (
 	"unsafe"
 )
 
-// These are called from exec_libc2.go in the child of fork.
-// 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 (
-	exitTrampoline = abi.FuncPCABI0(libc___exit_trampoline)
-	forkTrampoline = abi.FuncPCABI0(libc___fork_trampoline)
-)
-
 type SockaddrDatalink struct {
 	Len    uint8
 	Family uint8
@@ -230,12 +202,11 @@ 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)
diff --git a/src/syscall/syscall_openbsd_libc.go b/src/syscall/syscall_openbsd_libc.go
index ff9fa002590..15b68fd0fcf 100644
--- a/src/syscall/syscall_openbsd_libc.go
+++ b/src/syscall/syscall_openbsd_libc.go
@@ -10,11 +10,6 @@ import (
 	"internal/abi"
 )
 
-var (
-	exitTrampoline = abi.FuncPCABI0(libc_exit_trampoline)
-	forkTrampoline = abi.FuncPCABI0(libc_fork_trampoline)
-)
-
 func init() {
 	execveOpenBSD = execve
 }
diff --git a/src/syscall/zsyscall_darwin_amd64.go b/src/syscall/zsyscall_darwin_amd64.go
index 2ad03801b2e..0ccdaf2d0ee 100644
--- a/src/syscall/zsyscall_darwin_amd64.go
+++ b/src/syscall/zsyscall_darwin_amd64.go
@@ -1714,8 +1714,8 @@ func libc_munmap_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func __fork() (pid int, err error) {
-	r0, _, e1 := rawSyscall(abi.FuncPCABI0(libc___fork_trampoline), 0, 0, 0)
+func fork() (pid int, err error) {
+	r0, _, e1 := rawSyscall(abi.FuncPCABI0(libc_fork_trampoline), 0, 0, 0)
 	pid = int(r0)
 	if e1 != 0 {
 		err = errnoErr(e1)
@@ -1723,9 +1723,9 @@ 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
 
@@ -1781,20 +1781,6 @@ 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 {
diff --git a/src/syscall/zsyscall_darwin_amd64.s b/src/syscall/zsyscall_darwin_amd64.s
index 1815703803d..563083d441a 100644
--- a/src/syscall/zsyscall_darwin_amd64.s
+++ b/src/syscall/zsyscall_darwin_amd64.s
@@ -219,16 +219,14 @@ 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
-	JMP	libc___fork(SB)
+TEXT ·libc_fork_trampoline(SB),NOSPLIT,$0-0
+	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
diff --git a/src/syscall/zsyscall_darwin_arm64.go b/src/syscall/zsyscall_darwin_arm64.go
index 559bb49c4bc..09bf34bb3c5 100644
--- a/src/syscall/zsyscall_darwin_arm64.go
+++ b/src/syscall/zsyscall_darwin_arm64.go
@@ -1714,8 +1714,8 @@ func libc_munmap_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func __fork() (pid int, err error) {
-	r0, _, e1 := rawSyscall(abi.FuncPCABI0(libc___fork_trampoline), 0, 0, 0)
+func fork() (pid int, err error) {
+	r0, _, e1 := rawSyscall(abi.FuncPCABI0(libc_fork_trampoline), 0, 0, 0)
 	pid = int(r0)
 	if e1 != 0 {
 		err = errnoErr(e1)
@@ -1723,9 +1723,9 @@ 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
 
@@ -1781,20 +1781,6 @@ 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 {
diff --git a/src/syscall/zsyscall_darwin_arm64.s b/src/syscall/zsyscall_darwin_arm64.s
index 1666cf985c3..0567a42fa33 100644
--- a/src/syscall/zsyscall_darwin_arm64.s
+++ b/src/syscall/zsyscall_darwin_arm64.s
@@ -219,16 +219,14 @@ 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
-	JMP	libc___fork(SB)
+TEXT ·libc_fork_trampoline(SB),NOSPLIT,$0-0
+	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