cmd/internal/obj: fix indirect tail call code

The assembler isn't handling this correctly for most architectures.
Of course, the two I tried first, arm64 and amd64, worked, so I assumed
other archs could handle it also. Apparently not.

Should fix dashboard failures introduced by CL 751465.

Change-Id: I9fc4f123d11acf3d10cc9806abfb93ec077509a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/752560
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

6 files changed, 67 insertions, 25 deletions

diff --git a/src/cmd/internal/obj/arm/obj5.go b/src/cmd/internal/obj/arm/obj5.go
index 79f08a41ea..62870731b5 100644
--- a/src/cmd/internal/obj/arm/obj5.go
+++ b/src/cmd/internal/obj/arm/obj5.go
@@ -352,16 +352,25 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 
 		case obj.ARET:
 			nocache(p)
+
+			retSym, retReg := p.To.Sym, p.To.Reg
+			if retReg == obj.REG_NONE {
+				retReg = REGLINK
+			}
+			p.To.Sym = nil
+			p.To.Name = obj.NAME_NONE
+			p.To.Reg = obj.REG_NONE
+
 			if cursym.Func().Text.Mark&LEAF != 0 {
 				if autosize == 0 {
 					p.As = AB
 					p.From = obj.Addr{}
-					if p.To.Sym != nil { // retjmp
+					if retSym != nil { // retjmp
 						p.To.Type = obj.TYPE_BRANCH
 					} else {
 						p.To.Type = obj.TYPE_MEM
 						p.To.Offset = 0
-						p.To.Reg = REGLINK
+						p.To.Reg = retReg
 					}
 
 					break
@@ -380,14 +389,17 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			// this ARET, they come from a branch
 			// with the same stackframe, so no spadj.
 
-			if p.To.Sym != nil { // retjmp
+			if retSym != nil || retReg != REGLINK { // retjmp
 				p.To.Reg = REGLINK
 				q2 = obj.Appendp(p, newprog)
 				q2.As = AB
-				q2.To.Type = obj.TYPE_BRANCH
-				q2.To.Sym = p.To.Sym
-				p.To.Sym = nil
-				p.To.Name = obj.NAME_NONE
+				if retSym != nil {
+					q2.To.Type = obj.TYPE_BRANCH
+					q2.To.Sym = retSym
+				} else {
+					q2.To.Type = obj.TYPE_MEM
+					q2.To.Reg = retReg
+				}
 				p = q2
 			}
 
diff --git a/src/cmd/internal/obj/loong64/obj.go b/src/cmd/internal/obj/loong64/obj.go
index 51a28d130c..fcf10d2307 100644
--- a/src/cmd/internal/obj/loong64/obj.go
+++ b/src/cmd/internal/obj/loong64/obj.go
@@ -359,9 +359,13 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				break
 			}
 
-			retSym := p.To.Sym
+			retSym, retReg := p.To.Sym, p.To.Reg
+			if retReg == obj.REG_NONE {
+				retReg = REGLINK
+			}
 			p.To.Name = obj.NAME_NONE // clear fields as we may modify p to other instruction
 			p.To.Sym = nil
+			p.To.Reg = obj.REG_NONE
 
 			if c.cursym.Func().Text.Mark&LEAF != 0 {
 				if autosize == 0 {
@@ -373,7 +377,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 						p.To.Sym = retSym
 					} else {
 						p.To.Type = obj.TYPE_MEM
-						p.To.Reg = REGLINK
+						p.To.Reg = retReg
 						p.To.Offset = 0
 					}
 					p.Mark |= BRANCH
@@ -397,7 +401,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				} else {
 					q.To.Type = obj.TYPE_MEM
 					q.To.Offset = 0
-					q.To.Reg = REGLINK
+					q.To.Reg = retReg
 				}
 				q.Mark |= BRANCH
 				q.Spadj = +autosize
@@ -438,7 +442,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			} else {
 				q1.To.Type = obj.TYPE_MEM
 				q1.To.Offset = 0
-				q1.To.Reg = REGLINK
+				q1.To.Reg = retReg
 			}
 			q1.Mark |= BRANCH
 			q1.Spadj = +autosize
diff --git a/src/cmd/internal/obj/mips/obj0.go b/src/cmd/internal/obj/mips/obj0.go
index bbed88e9d6..4ade03a778 100644
--- a/src/cmd/internal/obj/mips/obj0.go
+++ b/src/cmd/internal/obj/mips/obj0.go
@@ -364,9 +364,13 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				break
 			}
 
-			retSym := p.To.Sym
+			retSym, retReg := p.To.Sym, p.To.Reg
+			if retReg == obj.REG_NONE {
+				retReg = REGLINK
+			}
 			p.To.Name = obj.NAME_NONE // clear fields as we may modify p to other instruction
 			p.To.Sym = nil
+			p.To.Reg = obj.REG_NONE
 
 			if c.cursym.Func().Text.Mark&LEAF != 0 {
 				if autosize == 0 {
@@ -378,7 +382,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 						p.To.Sym = retSym
 					} else {
 						p.To.Type = obj.TYPE_MEM
-						p.To.Reg = REGLINK
+						p.To.Reg = retReg
 						p.To.Offset = 0
 					}
 					p.Mark |= BRANCH
@@ -401,7 +405,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 					q.To.Sym = retSym
 				} else {
 					q.To.Type = obj.TYPE_MEM
-					q.To.Reg = REGLINK
+					q.To.Reg = retReg
 					q.To.Offset = 0
 				}
 				q.Mark |= BRANCH
@@ -443,7 +447,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			} else {
 				q1.To.Type = obj.TYPE_MEM
 				q1.To.Offset = 0
-				q1.To.Reg = REGLINK
+				q1.To.Reg = retReg
 			}
 			q1.Mark |= BRANCH
 			q1.Spadj = +autosize
diff --git a/src/cmd/internal/obj/ppc64/obj9.go b/src/cmd/internal/obj/ppc64/obj9.go
index bae2965639..323420fefa 100644
--- a/src/cmd/internal/obj/ppc64/obj9.go
+++ b/src/cmd/internal/obj/ppc64/obj9.go
@@ -965,7 +965,23 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				break
 			}
 
-			retTarget := p.To.Sym
+			retTarget, retReg := p.To.Sym, p.To.Reg
+			if retReg == obj.REG_NONE {
+				retReg = REG_LR
+			} else {
+				// Move target address into REG_CTR.
+				// (Indirect branches can only go to REG_LR or REG_CTR.)
+				x := newprog()
+				*x = *p
+				p.As = AMOVD
+				p.From.Type = obj.TYPE_REG
+				p.From.Reg = retReg
+				p.To.Type = obj.TYPE_REG
+				p.To.Reg = REG_CTR
+				retReg = REG_CTR
+				p.Link = x
+				p = x
+			}
 
 			if c.cursym.Func().Text.Mark&LEAF != 0 {
 				if autosize == 0 {
@@ -973,7 +989,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 					p.From = obj.Addr{}
 					if retTarget == nil {
 						p.To.Type = obj.TYPE_REG
-						p.To.Reg = REG_LR
+						p.To.Reg = retReg
 					} else {
 						p.To.Type = obj.TYPE_BRANCH
 						p.To.Sym = retTarget
@@ -994,7 +1010,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				q.Pos = p.Pos
 				if retTarget == nil {
 					q.To.Type = obj.TYPE_REG
-					q.To.Reg = REG_LR
+					q.To.Reg = retReg
 				} else {
 					q.To.Type = obj.TYPE_BRANCH
 					q.To.Sym = retTarget
@@ -1063,7 +1079,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			q1.Pos = p.Pos
 			if retTarget == nil {
 				q1.To.Type = obj.TYPE_REG
-				q1.To.Reg = REG_LR
+				q1.To.Reg = retReg
 			} else {
 				q1.To.Type = obj.TYPE_BRANCH
 				q1.To.Sym = retTarget
diff --git a/src/cmd/internal/obj/riscv/obj.go b/src/cmd/internal/obj/riscv/obj.go
index 24e0a454cd..e9005fe0db 100644
--- a/src/cmd/internal/obj/riscv/obj.go
+++ b/src/cmd/internal/obj/riscv/obj.go
@@ -596,7 +596,10 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 
 		case obj.ARET:
 			// Replace RET with epilogue.
-			retJMP := p.To.Sym
+			retJMP, retReg := p.To.Sym, p.To.Reg
+			if retReg == obj.REG_NONE {
+				retReg = REG_LR
+			}
 
 			if stacksize != 0 {
 				// Restore LR.
@@ -621,7 +624,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				p.As = AJALR
 				p.From = obj.Addr{Type: obj.TYPE_REG, Reg: REG_ZERO}
 				p.Reg = obj.REG_NONE
-				p.To = obj.Addr{Type: obj.TYPE_REG, Reg: REG_LR}
+				p.To = obj.Addr{Type: obj.TYPE_REG, Reg: retReg}
 			}
 
 			// "Add back" the stack removed in the previous instruction.
diff --git a/src/cmd/internal/obj/s390x/objz.go b/src/cmd/internal/obj/s390x/objz.go
index 4bfc1f7b2c..d877589573 100644
--- a/src/cmd/internal/obj/s390x/objz.go
+++ b/src/cmd/internal/obj/s390x/objz.go
@@ -385,7 +385,10 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			}
 
 		case obj.ARET:
-			retTarget := p.To.Sym
+			retTarget, retReg := p.To.Sym, p.To.Reg
+			if retReg == obj.REG_NONE {
+				retReg = REG_LR
+			}
 
 			if c.cursym.Func().Text.Mark&LEAF != 0 {
 				if autosize == 0 {
@@ -393,7 +396,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 					p.From = obj.Addr{}
 					if retTarget == nil {
 						p.To.Type = obj.TYPE_REG
-						p.To.Reg = REG_LR
+						p.To.Reg = retReg
 					} else {
 						p.To.Type = obj.TYPE_BRANCH
 						p.To.Sym = retTarget
@@ -414,7 +417,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				q.From = obj.Addr{}
 				if retTarget == nil {
 					q.To.Type = obj.TYPE_REG
-					q.To.Reg = REG_LR
+					q.To.Reg = retReg
 				} else {
 					q.To.Type = obj.TYPE_BRANCH
 					q.To.Sym = retTarget
@@ -450,7 +453,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			q.From = obj.Addr{}
 			if retTarget == nil {
 				q.To.Type = obj.TYPE_REG
-				q.To.Reg = REG_LR
+				q.To.Reg = retReg
 			} else {
 				q.To.Type = obj.TYPE_BRANCH
 				q.To.Sym = retTarget