runtime: clean up funcID assignment

Large enum sets should be sorted by name when the
values don't matter, as they don't here. Do that.

Also replace the large switch with a map lookup.

This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.
This CL is, however, not windows/arm64-specific.
It is cleanup meant to make the port (and future ports) easier.

Change-Id: Ibe727b5d8866bf4c40c96020e1f4632bde7efd59
Reviewed-on: https://go-review.googlesource.com/c/go/+/288798
Trust: Russ Cox <rsc@golang.org>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 61 insertions, 78 deletions

diff --git a/src/cmd/internal/objabi/funcid.go b/src/cmd/internal/objabi/funcid.go
index 1d098ee172..e921a82c0c 100644
--- a/src/cmd/internal/objabi/funcid.go
+++ b/src/cmd/internal/objabi/funcid.go
@@ -4,6 +4,8 @@
 
 package objabi
 
+import "strings"
+
 // A FuncID identifies particular functions that need to be treated
 // specially by the runtime.
 // Note that in some situations involving plugins, there may be multiple
@@ -13,88 +15,69 @@ type FuncID uint8
 
 const (
 	FuncID_normal FuncID = iota // not a special function
-	FuncID_runtime_main
+	FuncID_asmcgocall
+	FuncID_asyncPreempt
+	FuncID_cgocallback
+	FuncID_debugCallV1
+	FuncID_externalthreadhandler
+	FuncID_gcBgMarkWorker
 	FuncID_goexit
+	FuncID_gogo
+	FuncID_gopanic
+	FuncID_handleAsyncEvent
 	FuncID_jmpdefer
 	FuncID_mcall
 	FuncID_morestack
 	FuncID_mstart
+	FuncID_panicwrap
 	FuncID_rt0_go
-	FuncID_asmcgocall
-	FuncID_sigpanic
 	FuncID_runfinq
-	FuncID_gcBgMarkWorker
-	FuncID_systemstack_switch
+	FuncID_runtime_main
+	FuncID_sigpanic
 	FuncID_systemstack
-	FuncID_cgocallback
-	FuncID_gogo
-	FuncID_externalthreadhandler
-	FuncID_debugCallV1
-	FuncID_gopanic
-	FuncID_panicwrap
-	FuncID_handleAsyncEvent
-	FuncID_asyncPreempt
+	FuncID_systemstack_switch
 	FuncID_wrapper // any autogenerated code (hash/eq algorithms, method wrappers, etc.)
 )
 
+var funcIDs = map[string]FuncID{
+	"asmcgocall":            FuncID_asmcgocall,
+	"asyncPreempt":          FuncID_asyncPreempt,
+	"cgocallback":           FuncID_cgocallback,
+	"debugCallV1":           FuncID_debugCallV1,
+	"externalthreadhandler": FuncID_externalthreadhandler,
+	"gcBgMarkWorker":        FuncID_gcBgMarkWorker,
+	"go":                    FuncID_rt0_go,
+	"goexit":                FuncID_goexit,
+	"gogo":                  FuncID_gogo,
+	"gopanic":               FuncID_gopanic,
+	"handleAsyncEvent":      FuncID_handleAsyncEvent,
+	"jmpdefer":              FuncID_jmpdefer,
+	"main":                  FuncID_runtime_main,
+	"mcall":                 FuncID_mcall,
+	"morestack":             FuncID_morestack,
+	"mstart":                FuncID_mstart,
+	"panicwrap":             FuncID_panicwrap,
+	"runfinq":               FuncID_runfinq,
+	"sigpanic":              FuncID_sigpanic,
+	"switch":                FuncID_systemstack_switch,
+	"systemstack":           FuncID_systemstack,
+
+	// Don't show in call stack but otherwise not special.
+	"deferreturn":       FuncID_wrapper,
+	"runOpenDeferFrame": FuncID_wrapper,
+	"reflectcallSave":   FuncID_wrapper,
+}
+
 // Get the function ID for the named function in the named file.
 // The function should be package-qualified.
 func GetFuncID(name string, isWrapper bool) FuncID {
 	if isWrapper {
 		return FuncID_wrapper
 	}
-	switch name {
-	case "runtime.main":
-		return FuncID_runtime_main
-	case "runtime.goexit":
-		return FuncID_goexit
-	case "runtime.jmpdefer":
-		return FuncID_jmpdefer
-	case "runtime.mcall":
-		return FuncID_mcall
-	case "runtime.morestack":
-		return FuncID_morestack
-	case "runtime.mstart":
-		return FuncID_mstart
-	case "runtime.rt0_go":
-		return FuncID_rt0_go
-	case "runtime.asmcgocall":
-		return FuncID_asmcgocall
-	case "runtime.sigpanic":
-		return FuncID_sigpanic
-	case "runtime.runfinq":
-		return FuncID_runfinq
-	case "runtime.gcBgMarkWorker":
-		return FuncID_gcBgMarkWorker
-	case "runtime.systemstack_switch":
-		return FuncID_systemstack_switch
-	case "runtime.systemstack":
-		return FuncID_systemstack
-	case "runtime.cgocallback":
-		return FuncID_cgocallback
-	case "runtime.gogo":
-		return FuncID_gogo
-	case "runtime.externalthreadhandler":
-		return FuncID_externalthreadhandler
-	case "runtime.debugCallV1":
-		return FuncID_debugCallV1
-	case "runtime.gopanic":
-		return FuncID_gopanic
-	case "runtime.panicwrap":
-		return FuncID_panicwrap
-	case "runtime.handleAsyncEvent":
-		return FuncID_handleAsyncEvent
-	case "runtime.asyncPreempt":
-		return FuncID_asyncPreempt
-	case "runtime.deferreturn":
-		// Don't show in the call stack (used when invoking defer functions)
-		return FuncID_wrapper
-	case "runtime.runOpenDeferFrame":
-		// Don't show in the call stack (used when invoking defer functions)
-		return FuncID_wrapper
-	case "runtime.reflectcallSave":
-		// Don't show in the call stack (used when invoking defer functions)
-		return FuncID_wrapper
+	if strings.HasPrefix(name, "runtime.") {
+		if id, ok := funcIDs[name[len("runtime."):]]; ok {
+			return id
+		}
 	}
 	return FuncID_normal
 }
diff --git a/src/runtime/symtab.go b/src/runtime/symtab.go
index 7667f23f1d..fc93c00c2d 100644
--- a/src/runtime/symtab.go
+++ b/src/runtime/symtab.go
@@ -308,27 +308,27 @@ type funcID uint8
 
 const (
 	funcID_normal funcID = iota // not a special function
-	funcID_runtime_main
+	funcID_asmcgocall
+	funcID_asyncPreempt
+	funcID_cgocallback
+	funcID_debugCallV1
+	funcID_externalthreadhandler
+	funcID_gcBgMarkWorker
 	funcID_goexit
+	funcID_gogo
+	funcID_gopanic
+	funcID_handleAsyncEvent
 	funcID_jmpdefer
 	funcID_mcall
 	funcID_morestack
 	funcID_mstart
+	funcID_panicwrap
 	funcID_rt0_go
-	funcID_asmcgocall
-	funcID_sigpanic
 	funcID_runfinq
-	funcID_gcBgMarkWorker
-	funcID_systemstack_switch
+	funcID_runtime_main
+	funcID_sigpanic
 	funcID_systemstack
-	funcID_cgocallback
-	funcID_gogo
-	funcID_externalthreadhandler
-	funcID_debugCallV1
-	funcID_gopanic
-	funcID_panicwrap
-	funcID_handleAsyncEvent
-	funcID_asyncPreempt
+	funcID_systemstack_switch
 	funcID_wrapper // any autogenerated code (hash/eq algorithms, method wrappers, etc.)
 )