cmd/internal/obj/x86, cmd/internal/ld, cmd/6l: 6g/asm -dynlink accesses global data via a GOT

Change-Id: I49862e177045369d6c94d6a58afbdace4f13cc96
Reviewed-on: https://go-review.googlesource.com/8237Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/6g/galign.go

@@ -61,6 +61,9 @@ func betypeinit() {
 		typedefs[2].Sameas = gc.TUINT32
 	}
 
+	if gc.Ctxt.Flag_dynlink {
+		gc.Thearch.ReservedRegs = append(gc.Thearch.ReservedRegs, x86.REG_R15)
+	}
 }
 
 func main() {

src/cmd/6g/reg.go

@@ -123,7 +123,9 @@ func BtoR(b uint64) int {
 		// BP is part of the calling convention if framepointer_enabled.
 		b &^= (1 << (x86.REG_BP - x86.REG_AX))
 	}
-
+	if gc.Ctxt.Flag_dynlink {
+		b &^= (1 << (x86.REG_R15 - x86.REG_AX))
+	}
 	if b == 0 {
 		return 0
 	}

src/cmd/6l/asm.go

@@ -332,6 +332,13 @@ func elfreloc1(r *ld.Reloc, sectoff int64) int {
 			return -1
 		}
 
+	case ld.R_GOTPCREL:
+		if r.Siz == 4 {
+			ld.Thearch.Vput(ld.R_X86_64_GOTPCREL | uint64(elfsym)<<32)
+		} else {
+			return -1
+		}
+
 	case ld.R_TLS:
 		if r.Siz == 4 {
 			if ld.Buildmode == ld.BuildmodeCShared {

src/cmd/asm/internal/flags/flags.go

@@ -19,6 +19,7 @@ var (
 	PrintOut   = flag.Bool("S", false, "print assembly and machine code")
 	TrimPath   = flag.String("trimpath", "", "remove prefix from recorded source file paths")
 	Shared     = flag.Bool("shared", false, "generate code that can be linked into a shared library")
+	Dynlink    = flag.Bool("dynlink", false, "support references to Go symbols defined in other shared libraries")
 )
 
 var (

src/cmd/asm/main.go

@@ -41,7 +41,8 @@ func main() {
 		ctxt.Debugasm = 1
 	}
 	ctxt.Trimpath = *flags.TrimPath
-	if *flags.Shared {
+	ctxt.Flag_dynlink = *flags.Dynlink
+	if *flags.Shared || *flags.Dynlink {
 		ctxt.Flag_shared = 1
 	}
 	ctxt.Bso = obj.Binitw(os.Stdout)

src/cmd/internal/gc/lex.go

@@ -222,15 +222,22 @@ func Main() {
 	obj.Flagcount("x", "debug lexer", &Debug['x'])
 	obj.Flagcount("y", "debug declarations in canned imports (with -d)", &Debug['y'])
 	var flag_shared int
+	var flag_dynlink bool
 	if Thearch.Thechar == '6' {
 		obj.Flagcount("largemodel", "generate code that assumes a large memory model", &flag_largemodel)
 		obj.Flagcount("shared", "generate code that can be linked into a shared library", &flag_shared)
+		flag.BoolVar(&flag_dynlink, "dynlink", false, "support references to Go symbols defined in other shared libraries")
 	}
-
 	obj.Flagstr("cpuprofile", "file: write cpu profile to file", &cpuprofile)
 	obj.Flagstr("memprofile", "file: write memory profile to file", &memprofile)
 	obj.Flagparse(usage)
+
+	if flag_dynlink {
+		flag_shared = 1
+	}
 	Ctxt.Flag_shared = int32(flag_shared)
+	Ctxt.Flag_dynlink = flag_dynlink
+
 	Ctxt.Debugasm = int32(Debug['S'])
 	Ctxt.Debugvlog = int32(Debug['v'])
 

src/cmd/internal/ld/data.go

@@ -476,8 +476,8 @@ func relocsym(s *LSym) {
 			}
 
 			// r->sym can be null when CALL $(constant) is transformed from absolute PC to relative PC call.
-		case R_CALL, R_PCREL:
-			if Linkmode == LinkExternal && r.Sym != nil && r.Sym.Type != SCONST && r.Sym.Sect != Ctxt.Cursym.Sect {
+		case R_CALL, R_GOTPCREL, R_PCREL:
+			if Linkmode == LinkExternal && r.Sym != nil && r.Sym.Type != SCONST && (r.Sym.Sect != Ctxt.Cursym.Sect || r.Type == R_GOTPCREL) {
 				r.Done = 0
 
 				// set up addend for eventual relocation via outer symbol.

src/cmd/internal/ld/link.go

@@ -235,6 +235,7 @@ const (
 	R_PLT2
 	R_USEFIELD
 	R_POWER_TOC
+	R_GOTPCREL
 )
 
 // Reloc.variant

src/cmd/internal/obj/link.go

@@ -173,6 +173,9 @@ const (
 	NAME_STATIC
 	NAME_AUTO
 	NAME_PARAM
+	// A reference to name@GOT(SB) is a reference to the entry in the global offset
+	// table for 'name'.
+	NAME_GOTREF
 )
 
 const (
@@ -380,6 +383,7 @@ const (
 	R_PLT2
 	R_USEFIELD
 	R_POWER_TOC
+	R_GOTPCREL
 )
 
 type Auto struct {
@@ -431,6 +435,7 @@ type Link struct {
 	Debugdivmod        int32
 	Debugpcln          int32
 	Flag_shared        int32
+	Flag_dynlink       bool
 	Bso                *Biobuf
 	Pathname           string
 	Windows            int32

src/cmd/internal/obj/util.go

@@ -477,6 +477,9 @@ func Mconv(a *Addr) string {
 	case NAME_EXTERN:
 		str = fmt.Sprintf("%s%s(SB)", a.Sym.Name, offConv(a.Offset))
 
+	case NAME_GOTREF:
+		str = fmt.Sprintf("%s%s@GOT(SB)", a.Sym.Name, offConv(a.Offset))
+
 	case NAME_STATIC:
 		str = fmt.Sprintf("%s<>%s(SB)", a.Sym.Name, offConv(a.Offset))
 

src/cmd/internal/obj/x86/asm6.go

@@ -2028,6 +2028,7 @@ func oclass(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) int {
 	case obj.TYPE_ADDR:
 		switch a.Name {
 		case obj.NAME_EXTERN,
+			obj.NAME_GOTREF,
 			obj.NAME_STATIC:
 			if a.Sym != nil && isextern(a.Sym) || p.Mode == 32 {
 				return Yi32
@@ -2437,6 +2438,7 @@ func vaddr(ctxt *obj.Link, p *obj.Prog, a *obj.Addr, r *obj.Reloc) int64 {
 
 	switch a.Name {
 	case obj.NAME_STATIC,
+		obj.NAME_GOTREF,
 		obj.NAME_EXTERN:
 		s := a.Sym
 		if r == nil {
@@ -2444,7 +2446,10 @@ func vaddr(ctxt *obj.Link, p *obj.Prog, a *obj.Addr, r *obj.Reloc) int64 {
 			log.Fatalf("reloc")
 		}
 
-		if isextern(s) || p.Mode != 64 {
+		if a.Name == obj.NAME_GOTREF {
+			r.Siz = 4
+			r.Type = obj.R_GOTPCREL
+		} else if isextern(s) || p.Mode != 64 {
 			r.Siz = 4
 			r.Type = obj.R_ADDR
 		} else {
@@ -2519,6 +2524,7 @@ func asmandsz(ctxt *obj.Link, p *obj.Prog, a *obj.Addr, r int, rex int, m64 int)
 		base := int(a.Reg)
 		switch a.Name {
 		case obj.NAME_EXTERN,
+			obj.NAME_GOTREF,
 			obj.NAME_STATIC:
 			if !isextern(a.Sym) && p.Mode == 64 {
 				goto bad
@@ -2564,6 +2570,7 @@ func asmandsz(ctxt *obj.Link, p *obj.Prog, a *obj.Addr, r int, rex int, m64 int)
 	base = int(a.Reg)
 	switch a.Name {
 	case obj.NAME_STATIC,
+		obj.NAME_GOTREF,
 		obj.NAME_EXTERN:
 		if a.Sym == nil {
 			ctxt.Diag("bad addr: %v", p)
@@ -2582,7 +2589,10 @@ func asmandsz(ctxt *obj.Link, p *obj.Prog, a *obj.Addr, r int, rex int, m64 int)
 
 	ctxt.Rexflag |= regrex[base]&Rxb | rex
 	if base == REG_NONE || (REG_CS <= base && base <= REG_GS) || base == REG_TLS {
-		if (a.Sym == nil || !isextern(a.Sym)) && base == REG_NONE && (a.Name == obj.NAME_STATIC || a.Name == obj.NAME_EXTERN) || p.Mode != 64 {
+		if (a.Sym == nil || !isextern(a.Sym)) && base == REG_NONE && (a.Name == obj.NAME_STATIC || a.Name == obj.NAME_EXTERN || a.Name == obj.NAME_GOTREF) || p.Mode != 64 {
+			if a.Name == obj.NAME_GOTREF && (a.Offset != 0 || a.Index != 0 || a.Scale != 0) {
+				ctxt.Diag("%v has offset against gotref", p)
+			}
 			ctxt.Andptr[0] = byte(0<<6 | 5<<0 | r<<3)
 			ctxt.Andptr = ctxt.Andptr[1:]
 			goto putrelv

src/cmd/internal/obj/x86/obj6.go

@@ -297,6 +297,84 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 			p.From.Offset = 0
 		}
 	}
+
+	if ctxt.Flag_dynlink {
+		if p.As == ALEAQ && p.From.Type == obj.TYPE_MEM && p.From.Name == obj.NAME_EXTERN {
+			p.As = AMOVQ
+			p.From.Type = obj.TYPE_ADDR
+		}
+		if p.From.Type == obj.TYPE_ADDR && p.From.Name == obj.NAME_EXTERN {
+			if p.As != AMOVQ {
+				ctxt.Diag("do not know how to handle TYPE_ADDR in %v with -dynlink", p)
+			}
+			if p.To.Type != obj.TYPE_REG {
+				ctxt.Diag("do not know how to handle LEAQ-type insn to non-register in %v with -dynlink", p)
+			}
+			p.From.Type = obj.TYPE_MEM
+			p.From.Name = obj.NAME_GOTREF
+			if p.From.Offset != 0 {
+				q := obj.Appendp(ctxt, p)
+				q.As = AADDQ
+				q.From.Type = obj.TYPE_CONST
+				q.From.Offset = p.From.Offset
+				q.To = p.To
+				p.From.Offset = 0
+			}
+		}
+		if p.From3.Name == obj.NAME_EXTERN {
+			ctxt.Diag("don't know how to handle %v with -dynlink", p)
+		}
+		if p.To2.Name == obj.NAME_EXTERN {
+			ctxt.Diag("don't know how to handle %v with -dynlink", p)
+		}
+		var source *obj.Addr
+		if p.From.Name == obj.NAME_EXTERN {
+			if p.To.Name == obj.NAME_EXTERN {
+				ctxt.Diag("cannot handle NAME_EXTERN on both sides in %v with -dynlink", p)
+			}
+			source = &p.From
+		} else if p.To.Name == obj.NAME_EXTERN {
+			source = &p.To
+		} else {
+			return
+		}
+		if p.As == obj.ATEXT || p.As == obj.AFUNCDATA || p.As == obj.ACALL || p.As == obj.ARET || p.As == obj.AJMP {
+			return
+		}
+		if source.Type != obj.TYPE_MEM {
+			ctxt.Diag("don't know how to handle %v with -dynlink", p)
+		}
+		p1 := obj.Appendp(ctxt, p)
+		p2 := obj.Appendp(ctxt, p1)
+
+		p1.As = AMOVQ
+		p1.From.Type = obj.TYPE_MEM
+		p1.From.Sym = source.Sym
+		p1.From.Name = obj.NAME_GOTREF
+		p1.To.Type = obj.TYPE_REG
+		p1.To.Reg = REG_R15
+
+		p2.As = p.As
+		p2.From = p.From
+		p2.To = p.To
+		if p.From.Name == obj.NAME_EXTERN {
+			p2.From.Reg = REG_R15
+			p2.From.Name = obj.NAME_NONE
+			p2.From.Sym = nil
+		} else if p.To.Name == obj.NAME_EXTERN {
+			p2.To.Reg = REG_R15
+			p2.To.Name = obj.NAME_NONE
+			p2.To.Sym = nil
+		} else {
+			return
+		}
+		l := p.Link
+		l2 := p2.Link
+		*p = *p1
+		*p1 = *p2
+		p.Link = l
+		p1.Link = l2
+	}
 }
 
 func nacladdr(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) {

src/cmd/internal/obj/x86/obj6_test.go

+package x86_test
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"go/build"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+const testdata = `
+MOVQ AX, AX -> MOVQ AX, AX
+
+LEAQ name(SB), AX -> MOVQ name@GOT(SB), AX
+LEAQ name+10(SB), AX -> MOVQ name@GOT(SB), AX; ADDQ $10, AX
+MOVQ $name(SB), AX -> MOVQ name@GOT(SB), AX
+MOVQ $name+10(SB), AX -> MOVQ name@GOT(SB), AX; ADDQ $10, AX
+
+MOVQ name(SB), AX -> MOVQ name@GOT(SB), R15; MOVQ (R15), AX
+MOVQ name+10(SB), AX -> MOVQ name@GOT(SB), R15; MOVQ 10(R15), AX
+
+CMPQ name(SB), $0 -> MOVQ name@GOT(SB), R15; CMPQ (R15), $0
+
+MOVQ $1, name(SB) -> MOVQ name@GOT(SB), R15; MOVQ $1, (R15)
+MOVQ $1, name+10(SB) -> MOVQ name@GOT(SB), R15; MOVQ $1, 10(R15)
+`
+
+type ParsedTestData struct {
+	input              string
+	marks              []int
+	marker_to_input    map[int][]string
+	marker_to_expected map[int][]string
+	marker_to_output   map[int][]string
+}
+
+const marker_start = 1234
+
+func parseTestData(t *testing.T) *ParsedTestData {
+	r := &ParsedTestData{}
+	scanner := bufio.NewScanner(strings.NewReader(testdata))
+	r.marker_to_input = make(map[int][]string)
+	r.marker_to_expected = make(map[int][]string)
+	marker := marker_start
+	input_insns := []string{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		if len(strings.TrimSpace(line)) == 0 {
+			continue
+		}
+		parts := strings.Split(line, "->")
+		if len(parts) != 2 {
+			t.Fatalf("malformed line %v", line)
+		}
+		r.marks = append(r.marks, marker)
+		marker_insn := fmt.Sprintf("MOVQ $%d, AX", marker)
+		input_insns = append(input_insns, marker_insn)
+		for _, input_insn := range strings.Split(parts[0], ";") {
+			input_insns = append(input_insns, input_insn)
+			r.marker_to_input[marker] = append(r.marker_to_input[marker], normalize(input_insn))
+		}
+		for _, expected_insn := range strings.Split(parts[1], ";") {
+			r.marker_to_expected[marker] = append(r.marker_to_expected[marker], normalize(expected_insn))
+		}
+		marker++
+	}
+	r.input = "TEXT ·foo(SB),$0\n" + strings.Join(input_insns, "\n") + "\n"
+	return r
+}
+
+var spaces_re *regexp.Regexp = regexp.MustCompile("\\s+")
+var marker_re *regexp.Regexp = regexp.MustCompile("MOVQ \\$([0-9]+), AX")
+
+func normalize(s string) string {
+	return spaces_re.ReplaceAllLiteralString(strings.TrimSpace(s), " ")
+}
+
+func asmOutput(t *testing.T, s string) []byte {
+	tmpdir, err := ioutil.TempDir("", "progedittest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpdir)
+	tmpfile, err := os.Create(filepath.Join(tmpdir, "input.s"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer tmpfile.Close()
+	_, err = tmpfile.WriteString(s)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cmd := exec.Command(
+		build.Default.GOROOT+"/bin/go", "tool", "asm", "-S", "-dynlink",
+		"-o", filepath.Join(tmpdir, "output.6"), tmpfile.Name())
+
+	var env []string
+	for _, v := range os.Environ() {
+		if !strings.HasPrefix(v, "GOARCH=") {
+			env = append(env, v)
+		}
+	}
+	cmd.Env = append(env, "GOARCH=amd64")
+	asmout, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("error %s output %s", err, asmout)
+	}
+	return asmout
+}
+
+func parseOutput(t *testing.T, td *ParsedTestData, asmout []byte) {
+	scanner := bufio.NewScanner(bytes.NewReader(asmout))
+	marker := regexp.MustCompile("MOVQ \\$([0-9]+), AX")
+	mark := -1
+	td.marker_to_output = make(map[int][]string)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line[0] != '\t' {
+			continue
+		}
+		parts := strings.SplitN(line, "\t", 3)
+		if len(parts) != 3 {
+			continue
+		}
+		n := normalize(parts[2])
+		mark_matches := marker.FindStringSubmatch(n)
+		if mark_matches != nil {
+			mark, _ = strconv.Atoi(mark_matches[1])
+			if _, ok := td.marker_to_input[mark]; !ok {
+				t.Fatalf("unexpected marker %d", mark)
+			}
+		} else if mark != -1 {
+			td.marker_to_output[mark] = append(td.marker_to_output[mark], n)
+		}
+	}
+}
+
+func TestDynlink(t *testing.T) {
+	if runtime.GOOS == "nacl" || runtime.GOOS == "android" || (runtime.GOOS == "darwin" && runtime.GOARCH == "arm") {
+		// iOS and nacl cannot fork
+		t.Skipf("skipping on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+	testdata := parseTestData(t)
+	asmout := asmOutput(t, testdata.input)
+	parseOutput(t, testdata, asmout)
+	for _, m := range testdata.marks {
+		i := strings.Join(testdata.marker_to_input[m], "; ")
+		o := strings.Join(testdata.marker_to_output[m], "; ")
+		e := strings.Join(testdata.marker_to_expected[m], "; ")
+		if o != e {
+			if o == i {
+				t.Errorf("%s was unchanged; should have become %s", i, e)
+			} else {
+				t.Errorf("%s became %s; should have become %s", i, o, e)
+			}
+		} else if i != e {
+			t.Logf("%s correctly became %s", i, o)
+		}
+	}
+}