cmd/link: scope test to linux & net.sendFile

Limits the scope of new test added in 71c2bf5513.

Discussion: https://go-review.googlesource.com/c/go/+/684377.

Change-Id: I0e8f513eb564aae277ba8a80ebdad469eb1e6e6a
GitHub-Last-Rev: add2b2e209
GitHub-Pull-Request: golang/go#74720
Reviewed-on: https://go-review.googlesource.com/c/go/+/689916
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@google.com>

src/cmd/compile/internal/dwarfgen/dwarf.go

@@ -278,7 +278,7 @@ func createDwarfVars(fnsym *obj.LSym, complexOK bool, fn *ir.Func, apDecls []*ir
 				base.Fatalf("invalid heap allocated var without Heapaddr")
 			}
 			debug := fn.DebugInfo.(*ssa.FuncDebug)
-			list := createHeapDerefLocationList(n, fnsym, debug.EntryID, ssa.FuncEnd.ID)
+			list := createHeapDerefLocationList(n, debug.EntryID)
 			dvar.PutLocationList = func(listSym, startPC dwarf.Sym) {
 				debug.PutLocationList(list, base.Ctxt, listSym.(*obj.LSym), startPC.(*obj.LSym))
 			}
@@ -558,7 +558,7 @@ func createComplexVar(fnsym *obj.LSym, fn *ir.Func, varID ssa.VarID, closureVars
 
 // createHeapDerefLocationList creates a location list for a heap-escaped variable
 // that describes "dereference pointer at stack offset"
-func createHeapDerefLocationList(n *ir.Name, fnsym *obj.LSym, entryID, prologEndID ssa.ID) []byte {
+func createHeapDerefLocationList(n *ir.Name, entryID ssa.ID) []byte {
 	// Get the stack offset where the heap pointer is stored
 	heapPtrOffset := n.Heapaddr.FrameOffset()
 	if base.Ctxt.Arch.FixedFrameSize == 0 {

src/cmd/link/dwarf_test.go

@@ -257,7 +257,18 @@ func TestDWARFiOS(t *testing.T) {
 	})
 }
 
+// This test ensures that variables promoted to the heap, specifically
+// function return parameters, have correct location lists generated.
+//
+// TODO(deparker): This test is intentionally limited to GOOS=="linux"
+// and scoped to net.sendFile, which was the function reported originally in
+// issue #65405. There is relevant discussion in https://go-review.googlesource.com/c/go/+/684377
+// pertaining to these limitations. There are other missing location lists which must be fixed
+// particularly in functions where `linkname` is involved.
 func TestDWARFLocationList(t *testing.T) {
+	if runtime.GOOS != "linux" {
+		t.Skip("skipping test on non-linux OS")
+	}
 	testenv.MustHaveCGO(t)
 	testenv.MustHaveGoBuild(t)
 
@@ -305,22 +316,10 @@ func TestDWARFLocationList(t *testing.T) {
 		// Look for the net.sendFile subprogram
 		if entry.Tag == dwarf.TagSubprogram {
 			fnName, ok := entry.Val(dwarf.AttrName).(string)
-			if !ok {
+			if !ok || fnName != "net.sendFile" {
+				reader.SkipChildren()
 				continue
 			}
-			if strings.Contains(fnName, ".eq") || // Ignore autogenerated equality funcs
-				strings.HasPrefix(fnName, "internal/") || // Ignore internal/runtime package TODO(deparker): Fix these too (likely same issue as other ignored packages below).
-				strings.HasPrefix(fnName, "runtime.") || // Ignore runtime package which contain funcs implemented in assembly or exposed through linkname which seems to not generate location lists correctly (most likely linkname causing this). TODO(deparker) Fix these too.
-				strings.HasPrefix(fnName, "reflect.") || // Ignore reflect package. TODO(deparker) Fix these too.
-				strings.HasPrefix(fnName, "time.") { // Ignore funcs in time package which are exposed through linkname and seem to not generate location lists correctly TODO(deparker) Fix these too.
-				continue
-			}
-			if fnName == "syscall.compileCallback" || fnName == "maps.clone" {
-				continue // Ignore for now, possibly caused by linkname usage. TODO(deparker) Fix this too.
-			}
-			if runtime.GOOS == "windows" && strings.HasPrefix(fnName, "syscall.") {
-				continue // Ignore, caused by linkname usage. TODO(deparker) Fix these too.
-			}
 
 			for {
 				paramEntry, err := reader.Next()
@@ -332,13 +331,8 @@ func TestDWARFLocationList(t *testing.T) {
 				}
 
 				if paramEntry.Tag == dwarf.TagFormalParameter {
-					paramName, hasName := paramEntry.Val(dwarf.AttrName).(string)
+					paramName, _ := paramEntry.Val(dwarf.AttrName).(string)
-					if !hasName {
+
-						continue
-					}
-					if paramName[0] == '~' {
-						continue
-					}
 					// Check if this parameter has a location attribute
 					if loc := paramEntry.Val(dwarf.AttrLocation); loc != nil {
 						switch locData := loc.(type) {