cmd/internal/obj, cmd/link: access global data via a GOT in -dynlink mode on arm64

Change-Id: I6ca9406207e40c7c2c661075ccfe57b6600235cf
Reviewed-on: https://go-review.googlesource.com/13997
Reviewed-by: Ian Lance Taylor <iant@golang.org>

4 files changed, 135 insertions, 0 deletions

diff --git a/src/cmd/internal/obj/arm64/a.out.go b/src/cmd/internal/obj/arm64/a.out.go
index 06c4ea552d..d3e1e5ecbb 100644
--- a/src/cmd/internal/obj/arm64/a.out.go
+++ b/src/cmd/internal/obj/arm64/a.out.go
@@ -322,6 +322,9 @@ const (
 
 	C_ADDR // TODO(aram): explain difference from C_VCONADDR
 
+	// The GOT slot for a symbol in -dynlink mode.
+	C_GOTADDR
+
 	// TLS "var" in local exec mode: will become a constant offset from
 	// thread local base that is ultimately chosen by the program linker.
 	C_TLS_LE
diff --git a/src/cmd/internal/obj/arm64/anames7.go b/src/cmd/internal/obj/arm64/anames7.go
index f9df74ff89..2d17d17162 100644
--- a/src/cmd/internal/obj/arm64/anames7.go
+++ b/src/cmd/internal/obj/arm64/anames7.go
@@ -55,6 +55,7 @@ var cnames7 = []string{
 	"UOREG64K",
 	"LOREG",
 	"ADDR",
+	"GOTADDR",
 	"TLS_LE",
 	"TLS_IE",
 	"ROFF",
diff --git a/src/cmd/internal/obj/arm64/asm7.go b/src/cmd/internal/obj/arm64/asm7.go
index 243ff89817..38fe3ee92d 100644
--- a/src/cmd/internal/obj/arm64/asm7.go
+++ b/src/cmd/internal/obj/arm64/asm7.go
@@ -270,6 +270,7 @@ var optab = []Optab{
 	{AMOVH, C_ADDR, C_NONE, C_REG, 65, 12, 0, 0, 0},
 	{AMOVW, C_ADDR, C_NONE, C_REG, 65, 12, 0, 0, 0},
 	{AMOVD, C_ADDR, C_NONE, C_REG, 65, 12, 0, 0, 0},
+	{AMOVD, C_GOTADDR, C_NONE, C_REG, 71, 8, 0, 0, 0},
 	{AMOVD, C_TLS_LE, C_NONE, C_REG, 69, 4, 0, 0, 0},
 	{AMOVD, C_TLS_IE, C_NONE, C_REG, 70, 8, 0, 0, 0},
 	{AMUL, C_REG, C_REG, C_REG, 15, 4, 0, 0, 0},
@@ -981,6 +982,9 @@ func aclass(ctxt *obj.Link, a *obj.Addr) int {
 			}
 			return C_LEXT
 
+		case obj.NAME_GOTREF:
+			return C_GOTADDR
+
 		case obj.NAME_AUTO:
 			ctxt.Instoffset = int64(ctxt.Autosize) + a.Offset
 			return autoclass(ctxt.Instoffset)
@@ -2789,6 +2793,16 @@ func asmout(ctxt *obj.Link, p *obj.Prog, o *Optab, out []uint32) {
 			ctxt.Diag("invalid offset on MOVW $tlsvar")
 		}
 
+	case 71: /* movd sym@GOT, reg -> adrp REGTMP, #0; ldr reg, [REGTMP, #0] + relocs */
+		o1 = ADR(1, 0, REGTMP)
+		o2 = olsr12u(ctxt, int32(opldr12(ctxt, AMOVD)), 0, REGTMP, int(p.To.Reg))
+		rel := obj.Addrel(ctxt.Cursym)
+		rel.Off = int32(ctxt.Pc)
+		rel.Siz = 8
+		rel.Sym = p.From.Sym
+		rel.Add = 0
+		rel.Type = obj.R_ARM64_GOTPCREL
+
 	// This is supposed to be something that stops execution.
 	// It's not supposed to be reached, ever, but if it is, we'd
 	// like to be able to tell how we got there.  Assemble as
diff --git a/src/cmd/internal/obj/arm64/obj7.go b/src/cmd/internal/obj/arm64/obj7.go
index f6f8c71295..39330c6c12 100644
--- a/src/cmd/internal/obj/arm64/obj7.go
+++ b/src/cmd/internal/obj/arm64/obj7.go
@@ -250,6 +250,7 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 			s.Size = 4
 			p.From.Type = obj.TYPE_MEM
 			p.From.Sym = s
+			p.From.Sym.Local = true
 			p.From.Name = obj.NAME_EXTERN
 			p.From.Offset = 0
 		}
@@ -262,6 +263,7 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 			s.Size = 8
 			p.From.Type = obj.TYPE_MEM
 			p.From.Sym = s
+			p.From.Sym.Local = true
 			p.From.Name = obj.NAME_EXTERN
 			p.From.Offset = 0
 		}
@@ -287,6 +289,121 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 
 		break
 	}
+
+	if ctxt.Flag_dynlink {
+		rewriteToUseGot(ctxt, p)
+	}
+}
+
+// Rewrite p, if necessary, to access global data via the global offset table.
+func rewriteToUseGot(ctxt *obj.Link, p *obj.Prog) {
+	if p.As == obj.ADUFFCOPY || p.As == obj.ADUFFZERO {
+		//     ADUFFxxx $offset
+		// becomes
+		//     MOVD runtime.duffxxx@GOT, REGTMP
+		//     ADD $offset, REGTMP
+		//     CALL REGTMP
+		var sym *obj.LSym
+		if p.As == obj.ADUFFZERO {
+			sym = obj.Linklookup(ctxt, "runtime.duffzero", 0)
+		} else {
+			sym = obj.Linklookup(ctxt, "runtime.duffcopy", 0)
+		}
+		offset := p.To.Offset
+		p.As = AMOVD
+		p.From.Type = obj.TYPE_MEM
+		p.From.Name = obj.NAME_GOTREF
+		p.From.Sym = sym
+		p.To.Type = obj.TYPE_REG
+		p.To.Reg = REGTMP
+		p.To.Name = obj.NAME_NONE
+		p.To.Offset = 0
+		p.To.Sym = nil
+		p1 := obj.Appendp(ctxt, p)
+		p1.As = AADD
+		p1.From.Type = obj.TYPE_CONST
+		p1.From.Offset = offset
+		p1.To.Type = obj.TYPE_REG
+		p1.To.Reg = REGTMP
+		p2 := obj.Appendp(ctxt, p1)
+		p2.As = obj.ACALL
+		p2.To.Type = obj.TYPE_REG
+		p2.To.Reg = REGTMP
+	}
+
+	// We only care about global data: NAME_EXTERN means a global
+	// symbol in the Go sense, and p.Sym.Local is true for a few
+	// internally defined symbols.
+	if p.From.Type == obj.TYPE_ADDR && p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local {
+		// MOVD $sym, Rx becomes MOVD sym@GOT, Rx
+		// MOVD $sym+<off>, Rx becomes MOVD sym@GOT, Rx; ADD <off>, Rx
+		if p.As != AMOVD {
+			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 = AADD
+			q.From.Type = obj.TYPE_CONST
+			q.From.Offset = p.From.Offset
+			q.To = p.To
+			p.From.Offset = 0
+		}
+	}
+	if p.From3 != nil && p.From3.Name == obj.NAME_EXTERN {
+		ctxt.Diag("don't know how to handle %v with -dynlink", p)
+	}
+	var source *obj.Addr
+	// MOVx sym, Ry becomes MOVD sym@GOT, REGTMP; MOVx (REGTMP), Ry
+	// MOVx Ry, sym becomes MOVD sym@GOT, REGTMP; MOVD Ry, (REGTMP)
+	// An addition may be inserted between the two MOVs if there is an offset.
+	if p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local {
+		if p.To.Name == obj.NAME_EXTERN && !p.To.Sym.Local {
+			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 && !p.To.Sym.Local {
+		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.Sym.Type == obj.STLSBSS {
+		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 = AMOVD
+	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 = REGTMP
+
+	p2.As = p.As
+	p2.From = p.From
+	p2.To = p.To
+	if p.From.Name == obj.NAME_EXTERN {
+		p2.From.Reg = REGTMP
+		p2.From.Name = obj.NAME_NONE
+		p2.From.Sym = nil
+	} else if p.To.Name == obj.NAME_EXTERN {
+		p2.To.Reg = REGTMP
+		p2.To.Name = obj.NAME_NONE
+		p2.To.Sym = nil
+	} else {
+		return
+	}
+	obj.Nopout(p)
 }
 
 func follow(ctxt *obj.Link, s *obj.LSym) {