cmd/6l: call runtime.addmoduledata from .init_array

Change-Id: I09e84161d106960a69972f5fc845a1e40c28e58f
Reviewed-on: https://go-review.googlesource.com/8331
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/6l/asm.go

@@ -61,7 +61,61 @@ func needlib(name string) int {
 	return 0
 }
 
+func Addcall(ctxt *ld.Link, s *ld.LSym, t *ld.LSym) int64 {
+	s.Reachable = true
+	i := s.Size
+	s.Size += 4
+	ld.Symgrow(ctxt, s, s.Size)
+	r := ld.Addrel(s)
+	r.Sym = t
+	r.Off = int32(i)
+	r.Type = ld.R_CALL
+	r.Siz = 4
+	return i + int64(r.Siz)
+}
+
 func gentext() {
+	if !ld.DynlinkingGo() {
+		return
+	}
+	addmoduledata := ld.Linklookup(ld.Ctxt, "runtime.addmoduledata", 0)
+	if addmoduledata.Type == ld.STEXT {
+		// we're linking a module containing the runtime -> no need for
+		// an init function
+		return
+	}
+	addmoduledata.Reachable = true
+	initfunc := ld.Linklookup(ld.Ctxt, "go.link.addmoduledata", 0)
+	initfunc.Type = ld.STEXT
+	initfunc.Local = true
+	initfunc.Reachable = true
+	o := func(op ...uint8) {
+		for _, op1 := range op {
+			ld.Adduint8(ld.Ctxt, initfunc, op1)
+		}
+	}
+	// 0000000000000000 <local.dso_init>:
+	//    0:	48 8d 3d 00 00 00 00 	lea    0x0(%rip),%rdi        # 7 <local.dso_init+0x7>
+	// 			3: R_X86_64_PC32	runtime.firstmoduledata-0x4
+	o(0x48, 0x8d, 0x3d)
+	ld.Addpcrelplus(ld.Ctxt, initfunc, ld.Linklookup(ld.Ctxt, "runtime.firstmoduledata", 0), 0)
+	//    7:	e8 00 00 00 00       	callq  c <local.dso_init+0xc>
+	// 			8: R_X86_64_PLT32	runtime.addmoduledata-0x4
+	o(0xe8)
+	Addcall(ld.Ctxt, initfunc, addmoduledata)
+	//    c:	c3                   	retq
+	o(0xc3)
+	if ld.Ctxt.Etextp != nil {
+		ld.Ctxt.Etextp.Next = initfunc
+	} else {
+		ld.Ctxt.Textp = initfunc
+	}
+	ld.Ctxt.Etextp = initfunc
+	initarray_entry := ld.Linklookup(ld.Ctxt, "go.link.addmoduledatainit", 0)
+	initarray_entry.Reachable = true
+	initarray_entry.Local = true
+	initarray_entry.Type = ld.SINITARR
+	ld.Addaddr(ld.Ctxt, initarray_entry, initfunc)
 }
 
 func adddynrela(rela *ld.LSym, s *ld.LSym, r *ld.Reloc) {

src/cmd/internal/ld/data.go

@@ -1331,10 +1331,15 @@ func dodata() {
 
 	sect.Length = uint64(datsize) - sect.Vaddr
 
+	hasinitarr := Linkshared
+
 	/* shared library initializer */
 	switch Buildmode {
 	case BuildmodeCArchive, BuildmodeCShared, BuildmodeShared:
-		// TODO(mwhudson): switch on Linkshared
+		hasinitarr = true
+	}
+
+	if hasinitarr {
 		sect := addsection(&Segdata, ".init_array", 06)
 		sect.Align = maxalign(s, SINITARR)
 		datsize = Rnd(datsize, int64(sect.Align))

src/cmd/internal/ld/elf.go

@@ -1658,9 +1658,15 @@ func doelf() {
 		Addstring(shstrtab, ".note.GNU-stack")
 	}
 
+	hasinitarr := Linkshared
+
+	/* shared library initializer */
 	switch Buildmode {
 	case BuildmodeCArchive, BuildmodeCShared, BuildmodeShared:
-		// TODO(mwhudson): switch on Linkshared
+		hasinitarr = true
+	}
+
+	if hasinitarr {
 		Addstring(shstrtab, ".init_array")
 		switch Thearch.Thechar {
 		case '6', '7', '9':

src/cmd/internal/ld/symtab.go

@@ -464,4 +464,11 @@ func symtab() {
 	// The rest of moduledata is zero initialized.
 	moduledata.Size = moduledatasize
 	Symgrow(Ctxt, moduledata, moduledatasize)
+
+	lastmoduledatap := Linklookup(Ctxt, "runtime.lastmoduledatap", 0)
+	if lastmoduledatap.Type != SDYNIMPORT {
+		lastmoduledatap.Type = SNOPTRDATA
+		lastmoduledatap.Size = 0 // overwrite existing value
+		Addaddr(Ctxt, lastmoduledatap, moduledata)
+	}
 }

src/runtime/asm_amd64.s

@@ -1692,3 +1692,10 @@ TEXT runtime·prefetchnta(SB),NOSPLIT,$0-8
 	MOVQ	addr+0(FP), AX
 	PREFETCHNTA	(AX)
 	RET
+
+// This is called from .init_array and follows the platform, not Go, ABI.
+TEXT runtime·addmoduledata(SB),NOSPLIT,$0-8
+	MOVQ	runtime·lastmoduledatap(SB), AX
+	MOVQ	DI, moduledata_next(AX)
+	MOVQ	DI, runtime·lastmoduledatap(SB)
+	RET

src/runtime/symtab.go

@@ -61,6 +61,7 @@ type moduledata struct {
 }
 
 var firstmoduledata moduledata  // linker symbol
+var lastmoduledatap *moduledata // linker symbol
 
 type functab struct {
 	entry   uintptr