address comments.

Signed-off-by: doujiang24 <doujiang24@gmail.com>

Author: doujiang24

src/cmd/cgo/doc.go

@@ -436,7 +436,7 @@ For example:
 	// #cgo noescape cFunctionName
 
 When a Go function calls a C function, it prepares for the C function to
-call back to a Go function. the #cgo nocallback directive may be used to
+call back to a Go function. The #cgo nocallback directive may be used to
 tell the compiler that these preparations are not necessary.
 If the nocallback directive is used and the C function does call back into
 Go code, the program will panic.

src/cmd/cgo/out.go

@@ -644,9 +644,9 @@ func (p *Package) writeDefsFunc(fgo2 io.Writer, n *Name, callsMalloc *bool) {
 		fmt.Fprintf(fgo2, "\t_Cgo_no_callback(false)\n")
 	}
 
-	// use _Cgo_keepalive instead of _Cgo_use when noescape & nocallback exist,
+	// Use _Cgo_keepalive instead of _Cgo_use when noescape & nocallback exist,
 	// so that the compiler won't force to escape them to heap.
-	// instead, make the compiler keep them alive by using _Cgo_keepalive.
+	// Instead, make the compiler keep them alive by using _Cgo_keepalive.
 	touchFunc := "_Cgo_use"
 	if p.noEscapes[n.C] && p.noCallbacks[n.C] {
 		touchFunc = "_Cgo_keepalive"

src/runtime/cgo.go

@@ -73,10 +73,11 @@ var cgoHasExtraM bool
 func cgoUse(any) { throw("cgoUse should not be called") }
 
 // cgoKeepAlive is called by cgo-generated code (using go:linkname to get at
-// an unexported name). Unlike cgoUse The calls serve one purposes:
-// 1) they keep the argument alive until the call site; the call is emitted after
-// the end of the (presumed) use of the argument by C.
-// cgoKeepAlive should not actually be called (see cgoAlwaysFalse).
+// an unexported name). This call keeps its argument alive until the call site;
+// cgo emits the call after the last possible use of the argument by C code.
+// cgoKeepAlive is marked in the cgo-generated code as //go:noescape, so
+// unlike cgoUse it does not force the argument to escape to the heap.
+// This is used to implement the #cgo noescape directive.
 func cgoKeepAlive(any) { throw("cgoKeepAlive should not be called") }
 
 // cgoAlwaysFalse is a boolean value that is always false.

src/runtime/testdata/testprogcgo/issue63739.go

@@ -4,11 +4,11 @@
 
 package main
 
-// This is for issue #56378.
-// After we retiring _Cgo_use for parameters, the compiler will treat the
-// parameters, start from the second, as non-alive. Then, they will be marked
-// as scalar in stackmap, which means the pointer won't be copied correctly
-// in copystack.
+// This is for issue #63739.
+// Ensure that parameters are kept alive until the end of the C call. If not,
+// then a stack copy at just the right time while calling into C might think
+// that any stack pointers are not alive and fail to update them, causing the C
+// function to see the old, no longer correct, pointer values.
 
 /*
 int add_from_multiple_pointers(int *a, int *b, int *c) {