1 files changed, 241 insertions, 0 deletions
diff --git a/src/runtime/debugcall.go b/src/runtime/debugcall.go
new file mode 100644
index 0000000..efc68a7
--- /dev/null
+++ b/src/runtime/debugcall.go
@@ -0,0 +1,241 @@
+// Copyright 2018 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.
+
+// +build amd64
+
+package runtime
+
+import "unsafe"
+
+const (
+	debugCallSystemStack = "executing on Go runtime stack"
+	debugCallUnknownFunc = "call from unknown function"
+	debugCallRuntime     = "call from within the Go runtime"
+	debugCallUnsafePoint = "call not at safe point"
+)
+
+func debugCallV1()
+func debugCallPanicked(val interface{})
+
+// debugCallCheck checks whether it is safe to inject a debugger
+// function call with return PC pc. If not, it returns a string
+// explaining why.
+//
+//go:nosplit
+func debugCallCheck(pc uintptr) string {
+	// No user calls from the system stack.
+	if getg() != getg().m.curg {
+		return debugCallSystemStack
+	}
+	if sp := getcallersp(); !(getg().stack.lo < sp && sp <= getg().stack.hi) {
+		// Fast syscalls (nanotime) and racecall switch to the
+		// g0 stack without switching g. We can't safely make
+		// a call in this state. (We can't even safely
+		// systemstack.)
+		return debugCallSystemStack
+	}
+
+	// Switch to the system stack to avoid overflowing the user
+	// stack.
+	var ret string
+	systemstack(func() {
+		f := findfunc(pc)
+		if !f.valid() {
+			ret = debugCallUnknownFunc
+			return
+		}
+
+		name := funcname(f)
+
+		switch name {
+		case "debugCall32",
+			"debugCall64",
+			"debugCall128",
+			"debugCall256",
+			"debugCall512",
+			"debugCall1024",
+			"debugCall2048",
+			"debugCall4096",
+			"debugCall8192",
+			"debugCall16384",
+			"debugCall32768",
+			"debugCall65536":
+			// These functions are allowed so that the debugger can initiate multiple function calls.
+			// See: https://golang.org/cl/161137/
+			return
+		}
+
+		// Disallow calls from the runtime. We could
+		// potentially make this condition tighter (e.g., not
+		// when locks are held), but there are enough tightly
+		// coded sequences (e.g., defer handling) that it's
+		// better to play it safe.
+		if pfx := "runtime."; len(name) > len(pfx) && name[:len(pfx)] == pfx {
+			ret = debugCallRuntime
+			return
+		}
+
+		// Check that this isn't an unsafe-point.
+		if pc != f.entry {
+			pc--
+		}
+		up := pcdatavalue(f, _PCDATA_UnsafePoint, pc, nil)
+		if up != _PCDATA_UnsafePointSafe {
+			// Not at a safe point.
+			ret = debugCallUnsafePoint
+		}
+	})
+	return ret
+}
+
+// debugCallWrap starts a new goroutine to run a debug call and blocks
+// the calling goroutine. On the goroutine, it prepares to recover
+// panics from the debug call, and then calls the call dispatching
+// function at PC dispatch.
+//
+// This must be deeply nosplit because there are untyped values on the
+// stack from debugCallV1.
+//
+//go:nosplit
+func debugCallWrap(dispatch uintptr) {
+	var lockedm bool
+	var lockedExt uint32
+	callerpc := getcallerpc()
+	gp := getg()
+
+	// Create a new goroutine to execute the call on. Run this on
+	// the system stack to avoid growing our stack.
+	systemstack(func() {
+		var args struct {
+			dispatch uintptr
+			callingG *g
+		}
+		args.dispatch = dispatch
+		args.callingG = gp
+		fn := debugCallWrap1
+		newg := newproc1(*(**funcval)(unsafe.Pointer(&fn)), unsafe.Pointer(&args), int32(unsafe.Sizeof(args)), gp, callerpc)
+
+		// If the current G is locked, then transfer that
+		// locked-ness to the new goroutine.
+		if gp.lockedm != 0 {
+			// Save lock state to restore later.
+			mp := gp.m
+			if mp != gp.lockedm.ptr() {
+				throw("inconsistent lockedm")
+			}
+
+			lockedm = true
+			lockedExt = mp.lockedExt
+
+			// Transfer external lock count to internal so
+			// it can't be unlocked from the debug call.
+			mp.lockedInt++
+			mp.lockedExt = 0
+
+			mp.lockedg.set(newg)
+			newg.lockedm.set(mp)
+			gp.lockedm = 0
+		}
+
+		// Mark the calling goroutine as being at an async
+		// safe-point, since it has a few conservative frames
+		// at the bottom of the stack. This also prevents
+		// stack shrinks.
+		gp.asyncSafePoint = true
+
+		// Stash newg away so we can execute it below (mcall's
+		// closure can't capture anything).
+		gp.schedlink.set(newg)
+	})
+
+	// Switch to the new goroutine.
+	mcall(func(gp *g) {
+		// Get newg.
+		newg := gp.schedlink.ptr()
+		gp.schedlink = 0
+
+		// Park the calling goroutine.
+		gp.waitreason = waitReasonDebugCall
+		if trace.enabled {
+			traceGoPark(traceEvGoBlock, 1)
+		}
+		casgstatus(gp, _Grunning, _Gwaiting)
+		dropg()
+
+		// Directly execute the new goroutine. The debug
+		// protocol will continue on the new goroutine, so
+		// it's important we not just let the scheduler do
+		// this or it may resume a different goroutine.
+		execute(newg, true)
+	})
+
+	// We'll resume here when the call returns.
+
+	// Restore locked state.
+	if lockedm {
+		mp := gp.m
+		mp.lockedExt = lockedExt
+		mp.lockedInt--
+		mp.lockedg.set(gp)
+		gp.lockedm.set(mp)
+	}
+
+	gp.asyncSafePoint = false
+}
+
+// debugCallWrap1 is the continuation of debugCallWrap on the callee
+// goroutine.
+func debugCallWrap1(dispatch uintptr, callingG *g) {
+	// Dispatch call and trap panics.
+	debugCallWrap2(dispatch)
+
+	// Resume the caller goroutine.
+	getg().schedlink.set(callingG)
+	mcall(func(gp *g) {
+		callingG := gp.schedlink.ptr()
+		gp.schedlink = 0
+
+		// Unlock this goroutine from the M if necessary. The
+		// calling G will relock.
+		if gp.lockedm != 0 {
+			gp.lockedm = 0
+			gp.m.lockedg = 0
+		}
+
+		// Switch back to the calling goroutine. At some point
+		// the scheduler will schedule us again and we'll
+		// finish exiting.
+		if trace.enabled {
+			traceGoSched()
+		}
+		casgstatus(gp, _Grunning, _Grunnable)
+		dropg()
+		lock(&sched.lock)
+		globrunqput(gp)
+		unlock(&sched.lock)
+
+		if trace.enabled {
+			traceGoUnpark(callingG, 0)
+		}
+		casgstatus(callingG, _Gwaiting, _Grunnable)
+		execute(callingG, true)
+	})
+}
+
+func debugCallWrap2(dispatch uintptr) {
+	// Call the dispatch function and trap panics.
+	var dispatchF func()
+	dispatchFV := funcval{dispatch}
+	*(*unsafe.Pointer)(unsafe.Pointer(&dispatchF)) = noescape(unsafe.Pointer(&dispatchFV))
+
+	var ok bool
+	defer func() {
+		if !ok {
+			err := recover()
+			debugCallPanicked(err)
+		}
+	}()
+	dispatchF()
+	ok = true
+}