cmd/link: split pe .text section into .text and .rdata

Fixes #24725

Change-Id: I2864b88315ab15be036e8940d0a5884d876698d6
Reviewed-on: https://go-review.googlesource.com/115975
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

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

@@ -1352,9 +1352,8 @@ func (ctxt *Link) dodata() {
 	/*
 	 * We finished data, begin read-only data.
 	 * Not all systems support a separate read-only non-executable data section.
-	 * ELF systems do.
+	 * ELF and Windows PE systems do.
 	 * OS X and Plan 9 do not.
-	 * Windows PE may, but if so we have not implemented it.
 	 * And if we're using external linking mode, the point is moot,
 	 * since it's not our decision; that code expects the sections in
 	 * segtext.
@@ -1362,6 +1361,8 @@ func (ctxt *Link) dodata() {
 	var segro *sym.Segment
 	if ctxt.IsELF && ctxt.LinkMode == LinkInternal {
 		segro = &Segrodata
+	} else if ctxt.HeadType == objabi.Hwindows {
+		segro = &Segrodata
 	} else {
 		segro = &Segtext
 	}
@@ -1940,6 +1941,9 @@ func (ctxt *Link) address() {
 		Segrodata.Vaddr = va
 		Segrodata.Fileoff = va - Segtext.Vaddr + Segtext.Fileoff
 		Segrodata.Filelen = 0
+		if ctxt.HeadType == objabi.Hwindows {
+			Segrodata.Fileoff = Segtext.Fileoff + uint64(Rnd(int64(Segtext.Length), PEFILEALIGN))
+		}
 		for _, s := range Segrodata.Sections {
 			va = uint64(Rnd(int64(va), int64(s.Align)))
 			s.Vaddr = va
@@ -1974,7 +1978,7 @@ func (ctxt *Link) address() {
 	Segdata.Fileoff = va - Segtext.Vaddr + Segtext.Fileoff
 	Segdata.Filelen = 0
 	if ctxt.HeadType == objabi.Hwindows {
-		Segdata.Fileoff = Segtext.Fileoff + uint64(Rnd(int64(Segtext.Length), PEFILEALIGN))
+		Segdata.Fileoff = Segrodata.Fileoff + uint64(Rnd(int64(Segrodata.Length), PEFILEALIGN))
 	}
 	if ctxt.HeadType == objabi.Hplan9 {
 		Segdata.Fileoff = Segtext.Fileoff + Segtext.Filelen

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

@@ -395,6 +395,7 @@ type peFile struct {
 	sections       []*peSection
 	stringTable    peStringTable
 	textSect       *peSection
+	rdataSect      *peSection
 	dataSect       *peSection
 	bssSect        *peSection
 	ctorsSect      *peSection
@@ -548,21 +549,24 @@ func (f *peFile) emitRelocations(ctxt *Link) {
 		return relocs
 	}
 
-	f.textSect.emitRelocations(ctxt.Out, func() int {
-		n := relocsect(Segtext.Sections[0], ctxt.Textp, Segtext.Vaddr)
-		for _, sect := range Segtext.Sections[1:] {
-			n += relocsect(sect, datap, Segtext.Vaddr)
-		}
-		return n
-	})
-
-	f.dataSect.emitRelocations(ctxt.Out, func() int {
-		var n int
-		for _, sect := range Segdata.Sections {
-			n += relocsect(sect, datap, Segdata.Vaddr)
-		}
-		return n
-	})
+	sects := []struct {
+		peSect *peSection
+		seg    *sym.Segment
+		syms   []*sym.Symbol
+	}{
+		{f.textSect, &Segtext, ctxt.Textp},
+		{f.rdataSect, &Segrodata, datap},
+		{f.dataSect, &Segdata, datap},
+	}
+	for _, s := range sects {
+		s.peSect.emitRelocations(ctxt.Out, func() int {
+			var n int
+			for _, sect := range s.seg.Sections {
+				n += relocsect(sect, s.syms, s.seg.Vaddr)
+			}
+			return n
+		})
+	}
 
 dwarfLoop:
 	for _, sect := range Segdwarf.Sections {
@@ -622,8 +626,11 @@ func (f *peFile) mapToPESection(s *sym.Symbol, linkmode LinkMode) (pesectidx int
 	if s.Sect.Seg == &Segtext {
 		return f.textSect.index, int64(uint64(s.Value) - Segtext.Vaddr), nil
 	}
+	if s.Sect.Seg == &Segrodata {
+		return f.rdataSect.index, int64(uint64(s.Value) - Segrodata.Vaddr), nil
+	}
 	if s.Sect.Seg != &Segdata {
-		return 0, 0, fmt.Errorf("could not map %s symbol with non .text or .data section", s.Name)
+		return 0, 0, fmt.Errorf("could not map %s symbol with non .text or .rdata or .data section", s.Name)
 	}
 	v := uint64(s.Value) - Segdata.Vaddr
 	if linkmode != LinkExternal {
@@ -904,7 +911,11 @@ func Peinit(ctxt *Link) {
 	}
 
 	if ctxt.LinkMode == LinkExternal {
-		PESECTALIGN = 0
+		// .rdata section will contain "masks" and "shifts" symbols, and they
+		// need to be aligned to 16-bytes. So make all sections aligned
+		// to 32-byte and mark them all IMAGE_SCN_ALIGN_32BYTES so external
+		// linker will honour that requirement.
+		PESECTALIGN = 32
 		PEFILEALIGN = 0
 	}
 
@@ -1325,6 +1336,19 @@ func Asmbpe(ctxt *Link) {
 	t.checkSegment(&Segtext)
 	pefile.textSect = t
 
+	ro := pefile.addSection(".rdata", int(Segrodata.Length), int(Segrodata.Length))
+	ro.characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ
+	if ctxt.LinkMode == LinkExternal {
+		// some data symbols (e.g. masks) end up in the .rdata section, and they normally
+		// expect larger alignment requirement than the default text section alignment.
+		ro.characteristics |= IMAGE_SCN_ALIGN_32BYTES
+	} else {
+		// TODO(brainman): should not need IMAGE_SCN_MEM_EXECUTE, but I do not know why it carshes without it
+		ro.characteristics |= IMAGE_SCN_MEM_EXECUTE
+	}
+	ro.checkSegment(&Segrodata)
+	pefile.rdataSect = ro
+
 	var d *peSection
 	if ctxt.LinkMode != LinkExternal {
 		d = pefile.addSection(".data", int(Segdata.Length), int(Segdata.Filelen))

src/cmd/nm/nm_test.go

@@ -126,6 +126,15 @@ func testGoExec(t *testing.T, iscgo, isexternallinker bool) {
 		names["main."+f[0]] = f[1]
 	}
 
+	runtimeSyms := map[string]string{
+		"runtime.text":      "T",
+		"runtime.etext":     "T",
+		"runtime.rodata":    "R",
+		"runtime.erodata":   "R",
+		"runtime.epclntab":  "R",
+		"runtime.noptrdata": "D",
+	}
+
 	out, err = exec.Command(testnmpath, exe).CombinedOutput()
 	if err != nil {
 		t.Fatalf("go tool nm: %v\n%s", err, string(out))
@@ -147,6 +156,12 @@ func testGoExec(t *testing.T, iscgo, isexternallinker bool) {
 		if _, found := dups[name]; found {
 			t.Errorf("duplicate name of %q is found", name)
 		}
+		if stype, found := runtimeSyms[name]; found {
+			if want, have := stype, strings.ToUpper(f[1]); have != want {
+				t.Errorf("want %s type for %s symbol, but have %s", want, name, have)
+			}
+			delete(runtimeSyms, name)
+		}
 	}
 	err = scanner.Err()
 	if err != nil {
@@ -155,6 +170,9 @@ func testGoExec(t *testing.T, iscgo, isexternallinker bool) {
 	if len(names) > 0 {
 		t.Errorf("executable is missing %v symbols", names)
 	}
+	if len(runtimeSyms) > 0 {
+		t.Errorf("executable is missing %v symbols", runtimeSyms)
+	}
 }
 
 func TestGoExec(t *testing.T) {