cmd/link: enhance linker's dwarf test

Couple of changes to the linker's dwarf test, including:

 - add some code to the DWARF tests inlining coverage to verify the
   call_file attribute attached to inlined routine DIEs. If function
   main.F is inlined into function main.G, we want to see that the
   call_file attribute in the inlined routine DIE for main.F is the
   same file as that reported for main.G.

 - fix a glitch with the way the DW_AT_decl_file attribute was
   being checked. The previous code relied on hard-coded indices
   into the line table files table, which is very brittle (since
   there is no requirement that files be ordered in any specific
   way). Instead, add machinery to look up the actual file string
   via the line table reader.

Change-Id: I44e71c69b6e676238cf4b805e7170de17b50939f
Reviewed-on: https://go-review.googlesource.com/c/go/+/196517
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

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

@@ -340,10 +340,10 @@ func main() {
 	}
 }
 
-func varDeclCoordsAndSubrogramDeclFile(t *testing.T, testpoint string, expectFile int, expectLine int, directive string) {
+func varDeclCoordsAndSubrogramDeclFile(t *testing.T, testpoint string, expectFile string, expectLine int, directive string) {
 	t.Parallel()
 
-	prog := fmt.Sprintf("package main\n\nfunc main() {\n%s\nvar i int\ni = i\n}\n", directive)
+	prog := fmt.Sprintf("package main\n%s\nfunc main() {\n\nvar i int\ni = i\n}\n", directive)
 
 	dir, err := ioutil.TempDir("", testpoint)
 	if err != nil {
@@ -399,9 +399,14 @@ func varDeclCoordsAndSubrogramDeclFile(t *testing.T, testpoint string, expectFil
 		t.Errorf("DW_AT_decl_line for i is %v, want %d", line, expectLine)
 	}
 
-	file := maindie.Val(dwarf.AttrDeclFile)
-	if file == nil || file.(int64) != 1 {
-		t.Errorf("DW_AT_decl_file for main is %v, want %d", file, expectFile)
+	fileIdx, fileIdxOK := maindie.Val(dwarf.AttrDeclFile).(int64)
+	if !fileIdxOK {
+		t.Errorf("missing or invalid DW_AT_decl_file for main")
+	}
+	file := ex.FileRef(t, d, mainIdx, fileIdx)
+	base := filepath.Base(file)
+	if base != expectFile {
+		t.Errorf("DW_AT_decl_file for main is %v, want %v", base, expectFile)
 	}
 }
 
@@ -412,7 +417,7 @@ func TestVarDeclCoordsAndSubrogramDeclFile(t *testing.T) {
 		t.Skip("skipping on plan9; no DWARF symbol table in executables")
 	}
 
-	varDeclCoordsAndSubrogramDeclFile(t, "TestVarDeclCoords", 1, 5, "")
+	varDeclCoordsAndSubrogramDeclFile(t, "TestVarDeclCoords", "test.go", 5, "")
 }
 
 func TestVarDeclCoordsWithLineDirective(t *testing.T) {
@@ -423,7 +428,7 @@ func TestVarDeclCoordsWithLineDirective(t *testing.T) {
 	}
 
 	varDeclCoordsAndSubrogramDeclFile(t, "TestVarDeclCoordsWithLineDirective",
-		2, 200, "//line /foobar.go:200")
+		"foobar.go", 202, "//line /foobar.go:200")
 }
 
 // Helper class for supporting queries on DIEs within a DWARF .debug_info
@@ -555,6 +560,49 @@ func (ex *examiner) Parent(idx int) *dwarf.Entry {
 	return ex.entryFromIdx(p)
 }
 
+// ParentCU returns the enclosing compilation unit DIE for the DIE
+// with a given index, or nil if for some reason we can't establish a
+// parent.
+func (ex *examiner) ParentCU(idx int) *dwarf.Entry {
+	for {
+		parentDie := ex.Parent(idx)
+		if parentDie == nil {
+			return nil
+		}
+		if parentDie.Tag == dwarf.TagCompileUnit {
+			return parentDie
+		}
+		idx = ex.idxFromOffset(parentDie.Offset)
+	}
+}
+
+// FileRef takes a given DIE by index and a numeric file reference
+// (presumably from a decl_file or call_file attribute), looks up the
+// reference in the .debug_line file table, and returns the proper
+// string for it. We need to know which DIE is making the reference
+// so as find the right compilation unit.
+func (ex *examiner) FileRef(t *testing.T, dw *dwarf.Data, dieIdx int, fileRef int64) string {
+
+	// Find the parent compilation unit DIE for the specified DIE.
+	cuDie := ex.ParentCU(dieIdx)
+	if cuDie == nil {
+		t.Fatalf("no parent CU DIE for DIE with idx %d?", dieIdx)
+		return ""
+	}
+	// Construct a line reader and then use it to get the file string.
+	lr, lrerr := dw.LineReader(cuDie)
+	if lrerr != nil {
+		t.Fatal("d.LineReader: ", lrerr)
+		return ""
+	}
+	files := lr.Files()
+	if fileRef < 0 || int(fileRef) > len(files)-1 {
+		t.Fatalf("examiner.FileRef: malformed file reference %d", fileRef)
+		return ""
+	}
+	return files[fileRef].Name
+}
+
 // Return a list of all DIEs with name 'name'. When searching for DIEs
 // by name, keep in mind that the returned results will include child
 // DIEs such as params/variables. For example, asking for all DIEs named
@@ -691,6 +739,22 @@ func main() {
 			}
 			exCount++
 
+			// Verify that the call_file attribute for the inlined
+			// instance is ok. In this case it should match the file
+			// for the main routine. To do this we need to locate the
+			// compilation unit DIE that encloses what we're looking
+			// at; this can be done with the examiner.
+			cf, cfOK := child.Val(dwarf.AttrCallFile).(int64)
+			if !cfOK {
+				t.Fatalf("no call_file attr for inlined subroutine at offset %v", child.Offset)
+			}
+			file := ex.FileRef(t, d, mainIdx, cf)
+			base := filepath.Base(file)
+			if base != "test.go" {
+				t.Errorf("bad call_file attribute, found '%s', want '%s'",
+					file, "test.go")
+			}
+
 			omap := make(map[dwarf.Offset]bool)
 
 			// Walk the child variables of the inlined routine. Each