runtime: migrate internal/syscall to internal/runtime

For #65355

Change-Id: I5fefe30dcb520159de565e61dafc74a740fc8730
Reviewed-on: https://go-review.googlesource.com/c/go/+/559715
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 67 insertions, 0 deletions

diff --git a/src/internal/runtime/syscall/syscall_linux.go b/src/internal/runtime/syscall/syscall_linux.go
new file mode 100644
index 0000000000..cb88659394
--- /dev/null
+++ b/src/internal/runtime/syscall/syscall_linux.go
@@ -0,0 +1,67 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package syscall provides the syscall primitives required for the runtime.
+package syscall
+
+import (
+	"unsafe"
+)
+
+// TODO(https://go.dev/issue/51087): This package is incomplete and currently
+// only contains very minimal support for Linux.
+
+// Syscall6 calls system call number 'num' with arguments a1-6.
+func Syscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr)
+
+// syscall_RawSyscall6 is a push linkname to export Syscall6 as
+// syscall.RawSyscall6.
+//
+// //go:uintptrkeepalive because the uintptr argument may be converted pointers
+// that need to be kept alive in the caller (this is implied for Syscall6 since
+// it has no body).
+//
+// //go:nosplit because stack copying does not account for uintptrkeepalive, so
+// the stack must not grow. Stack copying cannot blindly assume that all
+// uintptr arguments are pointers, because some values may look like pointers,
+// but not really be pointers, and adjusting their value would break the call.
+//
+// This is a separate wrapper because we can't export one function as two
+// names. The assembly implementations name themselves Syscall6 would not be
+// affected by a linkname.
+//
+//go:uintptrkeepalive
+//go:nosplit
+//go:linkname syscall_RawSyscall6 syscall.RawSyscall6
+func syscall_RawSyscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr) {
+	return Syscall6(num, a1, a2, a3, a4, a5, a6)
+}
+
+func EpollCreate1(flags int32) (fd int32, errno uintptr) {
+	r1, _, e := Syscall6(SYS_EPOLL_CREATE1, uintptr(flags), 0, 0, 0, 0, 0)
+	return int32(r1), e
+}
+
+var _zero uintptr
+
+func EpollWait(epfd int32, events []EpollEvent, maxev, waitms int32) (n int32, errno uintptr) {
+	var ev unsafe.Pointer
+	if len(events) > 0 {
+		ev = unsafe.Pointer(&events[0])
+	} else {
+		ev = unsafe.Pointer(&_zero)
+	}
+	r1, _, e := Syscall6(SYS_EPOLL_PWAIT, uintptr(epfd), uintptr(ev), uintptr(maxev), uintptr(waitms), 0, 0)
+	return int32(r1), e
+}
+
+func EpollCtl(epfd, op, fd int32, event *EpollEvent) (errno uintptr) {
+	_, _, e := Syscall6(SYS_EPOLL_CTL, uintptr(epfd), uintptr(op), uintptr(fd), uintptr(unsafe.Pointer(event)), 0, 0)
+	return e
+}
+
+func Eventfd(initval, flags int32) (fd int32, errno uintptr) {
+	r1, _, e := Syscall6(SYS_EVENTFD2, uintptr(initval), uintptr(flags), 0, 0, 0, 0)
+	return int32(r1), e
+}