cmd/internal/obj/arm: access global data via GOT on arm when -dynlink

Change-Id: I88034611f56cc06bb47b0c431075cc78ca8dbb09
Reviewed-on: https://go-review.googlesource.com/14188
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 126 insertions, 2 deletions

diff --git a/src/cmd/internal/obj/arm/asm5.go b/src/cmd/internal/obj/arm/asm5.go
index 3bf4a31729..87ebc842ef 100644
--- a/src/cmd/internal/obj/arm/asm5.go
+++ b/src/cmd/internal/obj/arm/asm5.go
@@ -981,6 +981,7 @@ func aclass(ctxt *obj.Link, a *obj.Addr) int {
 		return C_NONE
 
 	case obj.TYPE_REG:
+		ctxt.Instoffset = 0
 		if REG_R0 <= a.Reg && a.Reg <= REG_R15 {
 			return C_REG
 		}
@@ -1010,6 +1011,7 @@ func aclass(ctxt *obj.Link, a *obj.Addr) int {
 	case obj.TYPE_MEM:
 		switch a.Name {
 		case obj.NAME_EXTERN,
+			obj.NAME_GOTREF,
 			obj.NAME_STATIC:
 			if a.Sym == nil || a.Sym.Name == "" {
 				fmt.Printf("null sym external\n")
@@ -1130,6 +1132,7 @@ func aclass(ctxt *obj.Link, a *obj.Addr) int {
 			return C_LCON
 
 		case obj.NAME_EXTERN,
+			obj.NAME_GOTREF,
 			obj.NAME_STATIC:
 			s := a.Sym
 			if s == nil {
@@ -1589,7 +1592,7 @@ func asmout(ctxt *obj.Link, p *obj.Prog, o *Optab, out []uint32) {
 		aclass(ctxt, &p.To)
 
 		if ctxt.Instoffset != 0 {
-			ctxt.Diag("%v: doesn't support BL offset(REG) where offset != 0", p)
+			ctxt.Diag("%v: doesn't support BL offset(REG) with non-zero offset %d", p, ctxt.Instoffset)
 		}
 		o1 = oprrr(ctxt, ABL, int(p.Scond))
 		o1 |= (uint32(p.To.Reg) & 15) << 0
@@ -1644,7 +1647,11 @@ func asmout(ctxt *obj.Link, p *obj.Prog, o *Optab, out []uint32) {
 			rel.Add = p.To.Offset
 
 			if ctxt.Flag_shared != 0 {
-				rel.Type = obj.R_PCREL
+				if p.To.Name == obj.NAME_GOTREF {
+					rel.Type = obj.R_GOTPCREL
+				} else {
+					rel.Type = obj.R_PCREL
+				}
 				rel.Add += ctxt.Pc - p.Rel.Pc - 8
 			} else {
 				rel.Type = obj.R_ADDR
diff --git a/src/cmd/internal/obj/arm/obj5.go b/src/cmd/internal/obj/arm/obj5.go
index 00ab13ccc3..ae045049ee 100644
--- a/src/cmd/internal/obj/arm/obj5.go
+++ b/src/cmd/internal/obj/arm/obj5.go
@@ -129,6 +129,123 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 			p.From.Offset = 0
 		}
 	}
+
+	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
+		//     MOVW runtime.duffxxx@GOT, R9
+		//     ADD $offset, R9
+		//     CALL (R9)
+		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 = AMOVW
+		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 = REG_R9
+		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 = REG_R9
+		p2 := obj.Appendp(ctxt, p1)
+		p2.As = obj.ACALL
+		p2.To.Type = obj.TYPE_MEM
+		p2.To.Reg = REG_R9
+		return
+	}
+
+	// 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 {
+		// MOVW $sym, Rx becomes MOVW sym@GOT, Rx
+		// MOVW $sym+<off>, Rx becomes MOVW sym@GOT, Rx; ADD <off>, Rx
+		if p.As != AMOVW {
+			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 MOVW sym@GOT, R9; MOVx (R9), Ry
+	// MOVx Ry, sym becomes MOVW sym@GOT, R9; MOVx Ry, (R9)
+	// 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 = AMOVW
+	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_R9
+
+	p2.As = p.As
+	p2.From = p.From
+	p2.To = p.To
+	if p.From.Name == obj.NAME_EXTERN {
+		p2.From.Reg = REG_R9
+		p2.From.Name = obj.NAME_NONE
+		p2.From.Sym = nil
+	} else if p.To.Name == obj.NAME_EXTERN {
+		p2.To.Reg = REG_R9
+		p2.To.Name = obj.NAME_NONE
+		p2.To.Sym = nil
+	} else {
+		return
+	}
+	obj.Nopout(p)
 }
 
 // Prog.mark