gensyscall: replace syscall numbers with func pointers

Instead of numbers and big switch statement, store functions pointers
directly on the syscall struct. The big switch statement was impossible
to extend outside of gensyscall. These new function pairs do not have
this problem.

internal/simulation/gensyscall/main.go

@@ -98,7 +98,7 @@ func (o *outputSorter) append(key, value string) {
 }
 
 func (o *outputSorter) output() string {
-	slices.SortFunc(o.outputs, func(a, b outputWithSortKey) int {
+	slices.SortStableFunc(o.outputs, func(a, b outputWithSortKey) int {
 		return cmp.Compare(a.sortKey, b.sortKey)
 	})
 	var out strings.Builder
@@ -477,7 +477,6 @@ func writeSyscalls(outputPath string, syscalls []syscallInfo, isMachine bool) {
 	}
 
 	callers := newOutputSorter()
-	dispatches := newOutputSorter()
 	checks := newOutputSorter()
 	ifaces := newOutputSorter()
 	for _, info := range syscalls {
@@ -569,14 +568,6 @@ func writeSyscalls(outputPath string, syscalls []syscallInfo, isMachine bool) {
 			parseDispatchText += "\t\tsyscall.Complete()\n"
 		}
 
-		dispatchText := fmt.Sprintf("\tcase %s:\n", sysVal) +
-			"\t\t// called by (for find references):\n" +
-			fmt.Sprintf("\t\t_ = %s\n", "Syscall"+ifaceName) +
-			prepareDispatch +
-			fmt.Sprintf("\t\t%sos.%s(%s)\n", dispatchRet, ifaceName, strings.Join(dispatchArgs, ", ")) +
-			parseDispatchText
-		dispatches.append(sysName, dispatchText)
-
 		if info.sysVal == 0 {
 			checkText := fmt.Sprintf("\tcase %s:\n", sysVal) +
 				"\t\treturn true\n"
@@ -588,18 +579,24 @@ func writeSyscalls(outputPath string, syscalls []syscallInfo, isMachine bool) {
 
 		callerText := "//go:norace\n" +
 			fmt.Sprintf("func %s(%s)%s {\n", "Syscall"+ifaceName, strings.Join(callerArgs, ", "), callerRet) +
-			"\t// invokes (for go to definition):\n" +
-			fmt.Sprintf("\t_ = (*%s).%s\n", osTypeName, ifaceName) +
 			"\tsyscall := syscallabi.GetGoroutineLocalSyscall()\n" +
+			fmt.Sprintf("\tsyscall.Trampoline = trampoline%s\n", ifaceName) +
 			fmt.Sprintf("\tsyscall.OS = %s\n", osImplName) +
-			fmt.Sprintf("\tsyscall.Trap = %s\n", sysVal) +
 			prepareCaller +
 			fmt.Sprintf("\t%s.dispatchSyscall(syscall)\n", osImplName) +
 			parseCallerText +
 			cleanupCallerText +
 			"\treturn\n" +
 			"}\n\n"
 		callers.append(sysName, callerText)
+
+		dispatchText := "//go:norace\n" +
+			fmt.Sprintf("func trampoline%s(syscall *syscallabi.Syscall) {\n", ifaceName) +
+			prepareDispatch +
+			fmt.Sprintf("\t\t%ssyscall.OS.(*%s).%s(%s)\n", dispatchRet, osTypeName, ifaceName, strings.Join(dispatchArgs, ", ")) +
+			parseDispatchText +
+			"}\n\n"
+		callers.append(sysName, dispatchText)
 	}
 
 	output := ""
@@ -647,15 +644,7 @@ func (os *%s) dispatchSyscall(s *syscallabi.Syscall) {
 	os.dispatcher.Dispatch(s)
 }
 
-//go:norace
-func (os *%s) HandleSyscall(syscall *syscallabi.Syscall) {
-	switch (syscall.Trap) {
-`, osIfaceName, osTypeName, osTypeName, osTypeName) + dispatches.output() + `	default:
-		panic("bad")
-	}
-}
-
-` + callers.output()
+`, osIfaceName, osTypeName, osTypeName) + callers.output()
 
 	if !isMachine {
 		output += `