debug/dwarf: support DW_FORM_rnglistx aka formRnglistx

Change-Id: I7df915978af3488f46a27595a1b04d0d33f81f7b
Reviewed-on: https://go-review.googlesource.com/c/go/+/302369
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

5 files changed, 116 insertions, 5 deletions

diff --git a/src/debug/dwarf/entry.go b/src/debug/dwarf/entry.go
index 3fc73b8ead..9f5ac57080 100644
--- a/src/debug/dwarf/entry.go
+++ b/src/debug/dwarf/entry.go
@@ -317,7 +317,7 @@ const (
 	// the "mac" section.
 	ClassMacPtr
 
-	// ClassMacPtr represents values that are an int64 offset into
+	// ClassRangeListPtr represents values that are an int64 offset into
 	// the "rangelist" section.
 	ClassRangeListPtr
 
@@ -355,7 +355,7 @@ const (
 	// into the "loclists" section.
 	ClassLocList
 
-	// ClassRngList represents values that are an int64 offset
+	// ClassRngList represents values that are a uint64 offset
 	// from the base of the "rnglists" section.
 	ClassRngList
 
@@ -464,6 +464,35 @@ func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset, vers int) *Entry
 		return val
 	}
 
+	resolveRnglistx := func(rnglistsBase, off uint64) uint64 {
+		is64, _ := b.format.dwarf64()
+		if is64 {
+			off *= 8
+		} else {
+			off *= 4
+		}
+		off += rnglistsBase
+		if uint64(int(off)) != off {
+			b.error("DW_FORM_rnglistx offset out of range")
+		}
+
+		b1 := makeBuf(b.dwarf, b.format, "rnglists", 0, b.dwarf.rngLists)
+		b1.skip(int(off))
+		if is64 {
+			off = b1.uint64()
+		} else {
+			off = uint64(b1.uint32())
+		}
+		if b1.err != nil {
+			b.err = b1.err
+			return 0
+		}
+		if uint64(int(off)) != off {
+			b.error("DW_FORM_rnglistx indirect offset out of range")
+		}
+		return rnglistsBase + off
+	}
+
 	for i := range e.Field {
 		e.Field[i].Attr = a.field[i].attr
 		e.Field[i].Class = a.field[i].class
@@ -709,7 +738,21 @@ func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset, vers int) *Entry
 
 		// rnglist
 		case formRnglistx:
-			val = b.uint()
+			off := b.uint()
+
+			// We have to adjust by the rnglists_base of
+			// the compilation unit. This won't work if
+			// the program uses Reader.Seek to skip over
+			// the unit. Not much we can do about that.
+			var rnglistsBase int64
+			if cu != nil {
+				rnglistsBase, _ = cu.Val(AttrRnglistsBase).(int64)
+			} else if a.tag == TagCompileUnit {
+				delay = append(delay, delayed{i, off, formRnglistx})
+				break
+			}
+
+			val = resolveRnglistx(uint64(rnglistsBase), off)
 		}
 
 		e.Field[i].Val = val
@@ -734,6 +777,12 @@ func (b *buf) entry(cu *Entry, atab abbrevTable, ubase Offset, vers int) *Entry
 			if b.err != nil {
 				return nil
 			}
+		case formRnglistx:
+			rnglistsBase, _ := e.Val(AttrRnglistsBase).(int64)
+			e.Field[del.idx].Val = resolveRnglistx(uint64(rnglistsBase), del.off)
+			if b.err != nil {
+				return nil
+			}
 		}
 	}
 
@@ -993,8 +1042,15 @@ func (d *Data) Ranges(e *Entry) ([][2]uint64, error) {
 			return d.dwarf5Ranges(u, cu, base, ranges, ret)
 
 		case ClassRngList:
-			// TODO: support DW_FORM_rnglistx
-			return ret, nil
+			rnglist, ok := field.Val.(uint64)
+			if !ok {
+				return ret, nil
+			}
+			cu, base, err := d.baseAddressForEntry(e)
+			if err != nil {
+				return nil, err
+			}
+			return d.dwarf5Ranges(u, cu, base, int64(rnglist), ret)
 
 		default:
 			return ret, nil
diff --git a/src/debug/dwarf/entry_test.go b/src/debug/dwarf/entry_test.go
index b54f8b4f8d..1f41d742ea 100644
--- a/src/debug/dwarf/entry_test.go
+++ b/src/debug/dwarf/entry_test.go
@@ -84,6 +84,19 @@ func TestRangesSection(t *testing.T) {
 	testRanges(t, "testdata/ranges.elf", want)
 }
 
+func TestRangesRnglistx(t *testing.T) {
+	want := []wantRange{
+		{0x401000, [][2]uint64{{0x401020, 0x40102c}, {0x401000, 0x40101d}}},
+		{0x40101c, [][2]uint64{{0x401020, 0x40102c}, {0x401000, 0x40101d}}},
+		{0x40101d, nil},
+		{0x40101f, nil},
+		{0x401020, [][2]uint64{{0x401020, 0x40102c}, {0x401000, 0x40101d}}},
+		{0x40102b, [][2]uint64{{0x401020, 0x40102c}, {0x401000, 0x40101d}}},
+		{0x40102c, nil},
+	}
+	testRanges(t, "testdata/rnglistx.elf", want)
+}
+
 func testRanges(t *testing.T, name string, want []wantRange) {
 	d := elfData(t, name)
 	r := d.Reader()
diff --git a/src/debug/dwarf/line_test.go b/src/debug/dwarf/line_test.go
index b13818e8b5..9c6b6ff5b0 100644
--- a/src/debug/dwarf/line_test.go
+++ b/src/debug/dwarf/line_test.go
@@ -117,6 +117,29 @@ func TestLineELFClang(t *testing.T) {
 	testLineTable(t, want, files, elfData(t, "testdata/line-clang.elf"))
 }
 
+func TestLineRnglists(t *testing.T) {
+	// Test a newer file, generated by clang.
+	file := &LineFile{Name: "/usr/local/google/home/iant/foo.c"}
+	want := []LineEntry{
+		{Address: 0x401020, File: file, Line: 12, IsStmt: true},
+		{Address: 0x401020, File: file, Line: 13, Column: 12, IsStmt: true, PrologueEnd: true},
+		{Address: 0x401022, File: file, Line: 13, Column: 7},
+		{Address: 0x401024, File: file, Line: 17, Column: 1, IsStmt: true},
+		{Address: 0x401027, File: file, Line: 16, Column: 10, IsStmt: true},
+		{Address: 0x40102c, EndSequence: true},
+		{Address: 0x401000, File: file, Line: 2, IsStmt: true},
+		{Address: 0x401000, File: file, Line: 6, Column: 17, IsStmt: true, PrologueEnd: true},
+		{Address: 0x401002, File: file, Line: 6, Column: 3},
+		{Address: 0x401019, File: file, Line: 9, Column: 3, IsStmt: true},
+		{Address: 0x40101a, File: file, Line: 0, Column: 3},
+		{Address: 0x40101c, File: file, Line: 9, Column: 3},
+		{Address: 0x40101d, EndSequence: true},
+	}
+	files := [][]*LineFile{{file}}
+
+	testLineTable(t, want, files, elfData(t, "testdata/rnglistx.elf"))
+}
+
 func TestLineSeek(t *testing.T) {
 	d := elfData(t, "testdata/line-gcc.elf")
 
diff --git a/src/debug/dwarf/testdata/rnglistx.c b/src/debug/dwarf/testdata/rnglistx.c
new file mode 100644
index 0000000000..877043584d
--- /dev/null
+++ b/src/debug/dwarf/testdata/rnglistx.c
@@ -0,0 +1,19 @@
+// clang -gdwarf-5 -O2 -nostdlib
+
+__attribute__((noinline, cold))
+static int sum(int i) {
+  int j, s;
+
+  s = 0;
+  for (j = 0; j < i; j++) {
+    s += j * i;
+  }
+  return s;
+}
+
+int main(int argc, char** argv) {
+  if (argc == 0) {
+    return 0;
+  }
+  return sum(argc);
+}
diff --git a/src/debug/dwarf/testdata/rnglistx.elf b/src/debug/dwarf/testdata/rnglistx.elf
new file mode 100755
index 0000000000..c2d7f55479
--- /dev/null
+++ b/src/debug/dwarf/testdata/rnglistx.elf