cmd/link: C is gone, remove check for Go calling C

It looks like the compiler still uses the Cfunc flag for functions
marked as //go:systemstack, but if I'm reading this right, that
doesn't apply here and the linker no longer needs Cfunc.

Change-Id: I63b9192c2f52f41401263c29dc8dfd8be8a901a1
Reviewed-on: https://go-review.googlesource.com/20105
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/link/internal/ld/lib.go

@@ -2119,63 +2119,6 @@ func Diag(format string, args ...interface{}) {
 	}
 }
 
-func checkgo() {
-	if Debug['C'] == 0 {
-		return
-	}
-
-	// TODO(rsc,khr): Eventually we want to get to no Go-called C functions at all,
-	// which would simplify this logic quite a bit.
-
-	// Mark every Go-called C function with cfunc=2, recursively.
-	var changed int
-	var i int
-	var r *Reloc
-	var s *LSym
-	for {
-		changed = 0
-		for s = Ctxt.Textp; s != nil; s = s.Next {
-			if s.Cfunc == 0 || (s.Cfunc == 2 && s.Nosplit != 0) {
-				for i = 0; i < len(s.R); i++ {
-					r = &s.R[i]
-					if r.Sym == nil {
-						continue
-					}
-					if (r.Type == obj.R_CALL || r.Type == obj.R_CALLARM) && r.Sym.Type == obj.STEXT {
-						if r.Sym.Cfunc == 1 {
-							changed = 1
-							r.Sym.Cfunc = 2
-						}
-					}
-				}
-			}
-		}
-		if changed == 0 {
-			break
-		}
-	}
-
-	// Complain about Go-called C functions that can split the stack
-	// (that can be preempted for garbage collection or trigger a stack copy).
-	for s := Ctxt.Textp; s != nil; s = s.Next {
-		if s.Cfunc == 0 || (s.Cfunc == 2 && s.Nosplit != 0) {
-			for i = 0; i < len(s.R); i++ {
-				r = &s.R[i]
-				if r.Sym == nil {
-					continue
-				}
-				if (r.Type == obj.R_CALL || r.Type == obj.R_CALLARM) && r.Sym.Type == obj.STEXT {
-					if s.Cfunc == 0 && r.Sym.Cfunc == 2 && r.Sym.Nosplit == 0 {
-						fmt.Printf("Go %s calls C %s\n", s.Name, r.Sym.Name)
-					} else if s.Cfunc == 2 && s.Nosplit != 0 && r.Sym.Nosplit == 0 {
-						fmt.Printf("Go calls C %s calls %s\n", s.Name, r.Sym.Name)
-					}
-				}
-			}
-		}
-	}
-}
-
 func Rnd(v int64, r int64) int64 {
 	if r <= 0 {
 		return v

src/cmd/link/internal/ld/link.go

@@ -43,7 +43,6 @@ type LSym struct {
 	Type       int16
 	Version    int16
 	Dupok      uint8
-	Cfunc      uint8
 	External   uint8
 	Nosplit    uint8
 	Reachable  bool

src/cmd/link/internal/ld/objfile.go

@@ -265,7 +265,6 @@ overwrite:
 		s.Nosplit = rduint8(f)
 		v := rdint(f)
 		s.Leaf = uint8(v & 1)
-		s.Cfunc = uint8(v & 2)
 		n := rdint(f)
 		var a *Auto
 		for i := 0; i < n; i++ {
@@ -331,9 +330,6 @@ overwrite:
 		if s.Dupok != 0 {
 			fmt.Fprintf(ctxt.Bso, "dupok ")
 		}
-		if s.Cfunc != 0 {
-			fmt.Fprintf(ctxt.Bso, "cfunc ")
-		}
 		if s.Nosplit != 0 {
 			fmt.Fprintf(ctxt.Bso, "nosplit ")
 		}

src/cmd/link/internal/ld/pobj.go

@@ -194,7 +194,6 @@ func Ldmain() {
 		mark(Linklookup(Ctxt, "runtime.read_tls_fallback", 0))
 	}
 
-	checkgo()
 	checkstrdata()
 	deadcode()
 	callgraph()