syscall: use rawSyscall6 to call ptrace in forkAndExecInChild

On darwin and openbsd, the autogenerated ptrace wrapper is
nosplit because it is called from forkAndExecInChild.

This makes it difficult to modify and improve the underlying
syscall mechanism, as ptrace is almost over the nosplit limit.

We better call ptrace directly using rawSyscall6 in
forkAndExecInChild so that we can lift the ptrace nosplit
restriction to.

Doing so also fixes a long-standing inconsistency:
forkAndExecInChild is documented to only allow rawSyscall, but
the ptrace wrapper is using non-raw syscalls.

Updates #64113

Change-Id: Ibbbb218511561c1a5cb5b6d288a691f9738b14a6
Reviewed-on: https://go-review.googlesource.com/c/go/+/708575
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

10 files changed, 6 insertions, 17 deletions

diff --git a/src/syscall/exec_libc2.go b/src/syscall/exec_libc2.go
index a0579627a3..5de09dfe99 100644
--- a/src/syscall/exec_libc2.go
+++ b/src/syscall/exec_libc2.go
@@ -59,7 +59,6 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		r1              uintptr
 		nextfd          int
 		i               int
-		err             error
 		pgrp            _C_int
 		cred            *Credential
 		ngroups, groups uintptr
@@ -99,8 +98,12 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 
 	// Enable tracing if requested.
 	if sys.Ptrace {
-		if err = ptrace(PTRACE_TRACEME, 0, 0, 0); err != nil {
-			err1 = err.(Errno)
+		if runtime.GOOS == "ios" {
+			err1 = ENOSYS
+			goto childerror
+		}
+		_, _, err1 = rawSyscall6(abi.FuncPCABI0(libc_ptrace_trampoline), PTRACE_TRACEME, 0, 0, 0, 0, 0)
+		if err1 != 0 {
 			goto childerror
 		}
 	}
diff --git a/src/syscall/mksyscall.pl b/src/syscall/mksyscall.pl
index b46a3f9438..6be94c9c44 100755
--- a/src/syscall/mksyscall.pl
+++ b/src/syscall/mksyscall.pl
@@ -141,12 +141,6 @@ while(<>) {
 	# without reading the header.
 	$text .= "// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT\n\n";
 
-	if ((($darwin || ($openbsd && $libc)) && $func =~ /^ptrace(Ptr)?$/)) {
-		# The ptrace function is called from forkAndExecInChild where stack
-		# growth is forbidden.
-		$text .= "//go:nosplit\n"
-	}
-
 	# Go function header.
 	my $out_decl = @out ? sprintf(" (%s)", join(', ', @out)) : "";
 	$text .= sprintf "func %s(%s)%s {\n", $func, join(', ', @in), $out_decl;
diff --git a/src/syscall/zsyscall_darwin_amd64.go b/src/syscall/zsyscall_darwin_amd64.go
index 8812fb12cd..fe4a264ed2 100644
--- a/src/syscall/zsyscall_darwin_amd64.go
+++ b/src/syscall/zsyscall_darwin_amd64.go
@@ -2011,7 +2011,6 @@ func libc_fstatat64_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-//go:nosplit
 func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
 	if runtime.GOOS == "ios" {
 		panic("unimplemented")
diff --git a/src/syscall/zsyscall_darwin_arm64.go b/src/syscall/zsyscall_darwin_arm64.go
index 22b096349d..8fd7392d5b 100644
--- a/src/syscall/zsyscall_darwin_arm64.go
+++ b/src/syscall/zsyscall_darwin_arm64.go
@@ -2011,7 +2011,6 @@ func libc_fstatat_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-//go:nosplit
 func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
 	if runtime.GOOS == "ios" {
 		panic("unimplemented")
diff --git a/src/syscall/zsyscall_openbsd_386.go b/src/syscall/zsyscall_openbsd_386.go
index c8cf7f231b..d914e19da0 100644
--- a/src/syscall/zsyscall_openbsd_386.go
+++ b/src/syscall/zsyscall_openbsd_386.go
@@ -1839,7 +1839,6 @@ func libc_exit_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-//go:nosplit
 func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
 	_, _, e1 := syscall6(abi.FuncPCABI0(libc_ptrace_trampoline), uintptr(request), uintptr(pid), uintptr(addr), uintptr(data), 0, 0)
 	if e1 != 0 {
diff --git a/src/syscall/zsyscall_openbsd_amd64.go b/src/syscall/zsyscall_openbsd_amd64.go
index 9188756a87..5efe4cd868 100644
--- a/src/syscall/zsyscall_openbsd_amd64.go
+++ b/src/syscall/zsyscall_openbsd_amd64.go
@@ -1839,7 +1839,6 @@ func libc_exit_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-//go:nosplit
 func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
 	_, _, e1 := syscall6(abi.FuncPCABI0(libc_ptrace_trampoline), uintptr(request), uintptr(pid), uintptr(addr), uintptr(data), 0, 0)
 	if e1 != 0 {
diff --git a/src/syscall/zsyscall_openbsd_arm.go b/src/syscall/zsyscall_openbsd_arm.go
index ecdfa63672..db8ea482ef 100644
--- a/src/syscall/zsyscall_openbsd_arm.go
+++ b/src/syscall/zsyscall_openbsd_arm.go
@@ -1839,7 +1839,6 @@ func libc_exit_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-//go:nosplit
 func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
 	_, _, e1 := syscall6(abi.FuncPCABI0(libc_ptrace_trampoline), uintptr(request), uintptr(pid), uintptr(addr), uintptr(data), 0, 0)
 	if e1 != 0 {
diff --git a/src/syscall/zsyscall_openbsd_arm64.go b/src/syscall/zsyscall_openbsd_arm64.go
index d28d3c5e1e..673791c824 100644
--- a/src/syscall/zsyscall_openbsd_arm64.go
+++ b/src/syscall/zsyscall_openbsd_arm64.go
@@ -1839,7 +1839,6 @@ func libc_exit_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-//go:nosplit
 func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
 	_, _, e1 := syscall6(abi.FuncPCABI0(libc_ptrace_trampoline), uintptr(request), uintptr(pid), uintptr(addr), uintptr(data), 0, 0)
 	if e1 != 0 {
diff --git a/src/syscall/zsyscall_openbsd_ppc64.go b/src/syscall/zsyscall_openbsd_ppc64.go
index 0e6828bcaf..7e0dc88a4c 100644
--- a/src/syscall/zsyscall_openbsd_ppc64.go
+++ b/src/syscall/zsyscall_openbsd_ppc64.go
@@ -1839,7 +1839,6 @@ func libc_exit_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-//go:nosplit
 func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
 	_, _, e1 := syscall6(abi.FuncPCABI0(libc_ptrace_trampoline), uintptr(request), uintptr(pid), uintptr(addr), uintptr(data), 0, 0)
 	if e1 != 0 {
diff --git a/src/syscall/zsyscall_openbsd_riscv64.go b/src/syscall/zsyscall_openbsd_riscv64.go
index 920147074d..7b5a89ceac 100644
--- a/src/syscall/zsyscall_openbsd_riscv64.go
+++ b/src/syscall/zsyscall_openbsd_riscv64.go
@@ -1839,7 +1839,6 @@ func libc_exit_trampoline()
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-//go:nosplit
 func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
 	_, _, e1 := syscall6(abi.FuncPCABI0(libc_ptrace_trampoline), uintptr(request), uintptr(pid), uintptr(addr), uintptr(data), 0, 0)
 	if e1 != 0 {