cmd/internal/obj,etc: replace -shared with -buildmode=c-shared

Currently some compilers and the assembler take a -shared flag which
means approximately what the -buildmode=c-shared flag means in the
proposed "Go Execution Modes" document. As part of implementing other
modes, the term "shared" becomes horribly overloaded, so this adds a
-buildmode argument instead (which currently only handles
-buildmode=c-shared, no new behaviour here).

The compilers retain a -shared argument as an alias for
-buildmode=c-shared.  The assemblers in 1.4 did not support -shared and
the tool has a different name now in any case, so I don't see a reason
to maintain compatibility there.

Author: mwhudson

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

@@ -6,6 +6,7 @@
 package flags
 
 import (
+	"cmd/internal/obj"
 	"flag"
 	"fmt"
 	"os"
@@ -18,7 +19,7 @@ var (
 	OutputFile = flag.String("o", "", "output file; default foo.6 for /a/b/c/foo.s on amd64")
 	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")
+	Buildmode  = obj.Buildmode_None
 )
 
 var (
@@ -29,6 +30,7 @@ var (
 func init() {
 	flag.Var(&D, "D", "predefined symbol with optional simple value -D=identifer=value; can be set multiple times")
 	flag.Var(&I, "I", "include directory; can be set multiple times")
+	flag.Var(&Buildmode, "buildmode", "build mode to use")
 }
 
 // MultiFlag allows setting a value multiple times to collect a list, as in -I=dir1 -I=dir2.

src/cmd/asm/main.go

@@ -41,9 +41,7 @@ func main() {
 		ctxt.Debugasm = 1
 	}
 	ctxt.Trimpath = *flags.TrimPath
-	if *flags.Shared {
-		ctxt.Flag_shared = 1
-	}
+	ctxt.Buildmode = flags.Buildmode
 	ctxt.Bso = obj.Binitw(os.Stdout)
 	defer obj.Bflush(ctxt.Bso)
 	ctxt.Diag = log.Fatalf

src/cmd/internal/gc/lex.go

@@ -195,6 +195,7 @@ func Main() {
 	obj.Flagfn0("V", "print compiler version", doversion)
 	obj.Flagcount("W", "debug parse tree after type checking", &Debug['W'])
 	obj.Flagstr("asmhdr", "file: write assembly header to named file", &asmhdr)
+	flag.Var(&Ctxt.Buildmode, "buildmode", "build mode to use")
 	obj.Flagcount("complete", "compiling complete package (no C or assembly)", &pure_go)
 	obj.Flagstr("d", "list: print debug information about items in list", &debugstr)
 	obj.Flagcount("e", "no limit on number of errors reported", &Debug['e'])
@@ -231,7 +232,13 @@ func Main() {
 	obj.Flagstr("cpuprofile", "file: write cpu profile to file", &cpuprofile)
 	obj.Flagstr("memprofile", "file: write memory profile to file", &memprofile)
 	obj.Flagparse(usage)
-	Ctxt.Flag_shared = int32(flag_shared)
+	if flag_shared != 0 {
+		if Ctxt.Buildmode == obj.Buildmode_None {
+			Ctxt.Buildmode = obj.Buildmode_CShared
+		} else if Ctxt.Buildmode != obj.Buildmode_CShared {
+			log.Fatalf("-shared and -buildmode=%s are incompatible\n", Ctxt.Buildmode.String())
+		}
+	}
 	Ctxt.Debugasm = int32(Debug['S'])
 	Ctxt.Debugvlog = int32(Debug['v'])
 

src/cmd/internal/obj/arm/asm5.go

@@ -900,7 +900,7 @@ func addpool(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) {
 		t.To.Type = a.Type
 		t.To.Name = a.Name
 
-		if ctxt.Flag_shared != 0 && t.To.Sym != nil {
+		if needsPcrel(ctxt) && t.To.Sym != nil {
 			t.Pcrel = p
 		}
 
@@ -1352,7 +1352,7 @@ func buildop(ctxt *obj.Link) {
 	}
 	for n = 0; optab[n].as != obj.AXXX; n++ {
 		if optab[n].flag&LPCREL != 0 {
-			if ctxt.Flag_shared != 0 {
+			if needsPcrel(ctxt) {
 				optab[n].size += int8(optab[n].pcrelsiz)
 			} else {
 				optab[n].flag &^= LPCREL
@@ -1674,12 +1674,12 @@ func asmout(ctxt *obj.Link, p *obj.Prog, o *Optab, out []uint32) {
 			// its type declaration if necessary.
 			if rel.Sym == ctxt.Tlsg && ctxt.Tlsg.Type == 0 {
 				rel.Type = obj.R_TLS
-				if ctxt.Flag_shared != 0 {
+				if needsPcrel(ctxt) { //TODO(mwhudson): maybe this should be needsInitalExecTLS
 					rel.Add += ctxt.Pc - p.Pcrel.Pc - 8 - int64(rel.Siz)
 				}
 				rel.Xadd = rel.Add
 				rel.Xsym = rel.Sym
-			} else if ctxt.Flag_shared != 0 {
+			} else if needsPcrel(ctxt) {
 				rel.Type = obj.R_PCREL
 				rel.Add += ctxt.Pc - p.Pcrel.Pc - 8
 			} else {

src/cmd/internal/obj/arm/obj5.go

@@ -38,6 +38,22 @@ import (
 	"math"
 )
 
+func needsInitalExecTLS(ctxt *obj.Link) bool {
+	switch ctxt.Buildmode {
+	case obj.Buildmode_CShared:
+		return true
+	}
+	return false
+}
+
+func needsPcrel(ctxt *obj.Link) bool {
+	switch ctxt.Buildmode {
+	case obj.Buildmode_CShared:
+		return true
+	}
+	return false
+}
+
 var progedit_tlsfallback *obj.LSym
 
 func progedit(ctxt *obj.Link, p *obj.Prog) {
@@ -142,7 +158,7 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 		}
 	}
 
-	if ctxt.Flag_shared != 0 {
+	if needsInitalExecTLS(ctxt) {
 		// Shared libraries use R_ARM_TLS_IE32 instead of
 		// R_ARM_TLS_LE32, replacing the link time constant TLS offset in
 		// runtime.tlsg with an address to a GOT entry containing the
@@ -273,7 +289,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
 	for p := cursym.Text; p != nil; p = p.Link {
 		switch p.As {
 		case ACASE:
-			if ctxt.Flag_shared != 0 {
+			if needsPcrel(ctxt) {
 				linkcase(p)
 			}
 

src/cmd/internal/obj/flag.go

@@ -5,6 +5,7 @@
 package obj
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -118,3 +119,28 @@ func (f fn1) Set(s string) error {
 }
 
 func (f fn1) String() string { return "" }
+
+type Buildmode uint8
+
+const (
+	Buildmode_None Buildmode = iota
+	Buildmode_CShared
+)
+
+func (mode *Buildmode) Set(s string) error {
+	switch s {
+	default:
+		return errors.New("buildmode %s not recognized")
+	case "c-shared":
+		*mode = Buildmode_CShared
+	}
+	return nil
+}
+
+func (mode *Buildmode) String() string {
+	switch *mode {
+	case Buildmode_CShared:
+		return "c-shared"
+	}
+	return fmt.Sprintf("Buildmode(%d)", uint8(*mode))
+}

src/cmd/internal/obj/link.go

@@ -475,7 +475,7 @@ type Link struct {
 	Debugdivmod        int32
 	Debugfloat         int32
 	Debugpcln          int32
-	Flag_shared        int32
+	Buildmode          Buildmode
 	Iself              int32
 	Bso                *Biobuf
 	Pathname           string

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

@@ -1950,8 +1950,8 @@ func prefixof(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) int {
 				log.Fatalf("unknown TLS base register for %s", obj.Headstr(ctxt.Headtype))
 
 			case obj.Hlinux:
-				if ctxt.Flag_shared != 0 {
-					log.Fatalf("unknown TLS base register for linux with -shared")
+				if needsInitalExecTLS(ctxt) {
+					log.Fatalf("unknown TLS base register for linux with IE model")
 				} else {
 					return 0x64 // FS
 				}
@@ -1984,7 +1984,7 @@ func prefixof(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) int {
 		return 0x26
 
 	case REG_TLS:
-		if ctxt.Flag_shared != 0 {
+		if needsInitalExecTLS(ctxt) {
 			// When building for inclusion into a shared library, an instruction of the form
 			//     MOV 0(CX)(TLS*1), AX
 			// becomes
@@ -2624,7 +2624,7 @@ func asmandsz(ctxt *obj.Link, p *obj.Prog, a *obj.Addr, r int, rex int, m64 int)
 	}
 
 	if REG_AX <= base && base <= REG_R15 {
-		if a.Index == REG_TLS && ctxt.Flag_shared == 0 {
+		if a.Index == REG_TLS && needsInitalExecTLS(ctxt) {
 			rel = obj.Reloc{}
 			rel.Type = obj.R_TLS_IE
 			rel.Siz = 4
@@ -3834,8 +3834,8 @@ func doasm(ctxt *obj.Link, p *obj.Prog) {
 						log.Fatalf("unknown TLS base location for %s", obj.Headstr(ctxt.Headtype))
 
 					case obj.Hlinux:
-						if ctxt.Flag_shared == 0 {
-							log.Fatalf("unknown TLS base location for linux without -shared")
+						if !needsInitalExecTLS(ctxt) {
+							log.Fatalf("unknown TLS base location for linux with LE model")
 						}
 						// Note that this is not generating the same insn as the other cases.
 						//     MOV TLS, R_to

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

@@ -38,6 +38,14 @@ import (
 	"math"
 )
 
+func needsInitalExecTLS(ctxt *obj.Link) bool {
+	switch ctxt.Buildmode {
+	case obj.Buildmode_CShared:
+		return true
+	}
+	return false
+}
+
 func canuselocaltls(ctxt *obj.Link) bool {
 	if ctxt.Arch.Regsize == 4 {
 		switch ctxt.Headtype {
@@ -56,7 +64,7 @@ func canuselocaltls(ctxt *obj.Link) bool {
 		obj.Hwindows:
 		return false
 	case obj.Hlinux:
-		return ctxt.Flag_shared == 0
+		return !needsInitalExecTLS(ctxt)
 	}
 
 	return true