cmd/internal/obj/riscv: store relocation details in obj.Prog.RestArgs

Store the relocation offset and symbol in obj.Prog.RestArgs, rather than
overloading obj.Prog.From and having to deal with invalid offsets
potentially existing when the instruction is encoded.

Change-Id: Iff0d678361677e78b41b887f6eba08cee94fccb3
Reviewed-on: https://go-review.googlesource.com/c/go/+/218197
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 16 insertions, 30 deletions

diff --git a/src/cmd/internal/obj/riscv/obj.go b/src/cmd/internal/obj/riscv/obj.go
index 7add8e31c6..13eb9787d0 100644
--- a/src/cmd/internal/obj/riscv/obj.go
+++ b/src/cmd/internal/obj/riscv/obj.go
@@ -46,13 +46,12 @@ func jalrToSym(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc, lr int16) *ob
 
 	to := p.To
 
-	// This offset isn't really encoded with either instruction. It will be
-	// extracted for a relocation later.
 	p.As = AAUIPC
-	p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: to.Offset, Sym: to.Sym}
+	p.Mark |= NEED_PCREL_ITYPE_RELOC
+	p.RestArgs = []obj.Addr{obj.Addr{Type: obj.TYPE_CONST, Offset: to.Offset, Sym: to.Sym}}
+	p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: 0}
 	p.Reg = 0
 	p.To = obj.Addr{Type: obj.TYPE_REG, Reg: REG_TMP}
-	p.Mark |= NEED_PCREL_ITYPE_RELOC
 	p = obj.Appendp(p, newprog)
 
 	// Leave Sym only for the CALL reloc in assemble.
@@ -324,13 +323,12 @@ func rewriteMOV(ctxt *obj.Link, newprog obj.ProgAlloc, p *obj.Prog) {
 			as := p.As
 			to := p.To
 
-			// The offset is not really encoded with either instruction.
-			// It will be extracted later for a relocation.
 			p.As = AAUIPC
-			p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: p.From.Offset, Sym: p.From.Sym}
+			p.Mark |= NEED_PCREL_ITYPE_RELOC
+			p.RestArgs = []obj.Addr{obj.Addr{Type: obj.TYPE_CONST, Offset: p.From.Offset, Sym: p.From.Sym}}
+			p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: 0}
 			p.Reg = 0
 			p.To = obj.Addr{Type: obj.TYPE_REG, Reg: to.Reg}
-			p.Mark |= NEED_PCREL_ITYPE_RELOC
 			p = obj.Appendp(p, newprog)
 
 			p.As = movToLoad(as)
@@ -385,13 +383,12 @@ func rewriteMOV(ctxt *obj.Link, newprog obj.ProgAlloc, p *obj.Prog) {
 				as := p.As
 				from := p.From
 
-				// The offset is not really encoded with either instruction.
-				// It will be extracted later for a relocation.
 				p.As = AAUIPC
-				p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: p.To.Offset, Sym: p.To.Sym}
+				p.Mark |= NEED_PCREL_STYPE_RELOC
+				p.RestArgs = []obj.Addr{obj.Addr{Type: obj.TYPE_CONST, Offset: p.To.Offset, Sym: p.To.Sym}}
+				p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: 0}
 				p.Reg = 0
 				p.To = obj.Addr{Type: obj.TYPE_REG, Reg: REG_TMP}
-				p.Mark |= NEED_PCREL_STYPE_RELOC
 				p = obj.Appendp(p, newprog)
 
 				p.As = movToStore(as)
@@ -452,13 +449,12 @@ func rewriteMOV(ctxt *obj.Link, newprog obj.ProgAlloc, p *obj.Prog) {
 			// ADDI $off_lo, R
 			to := p.To
 
-			// The offset is not really encoded with either instruction.
-			// It will be extracted later for a relocation.
 			p.As = AAUIPC
-			p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: p.From.Offset, Sym: p.From.Sym}
+			p.Mark |= NEED_PCREL_ITYPE_RELOC
+			p.RestArgs = []obj.Addr{obj.Addr{Type: obj.TYPE_CONST, Offset: p.From.Offset, Sym: p.From.Sym}}
+			p.From = obj.Addr{Type: obj.TYPE_CONST, Offset: 0}
 			p.Reg = 0
 			p.To = to
-			p.Mark |= NEED_PCREL_ITYPE_RELOC
 			p = obj.Appendp(p, newprog)
 
 			p.As = AADDI
@@ -1413,13 +1409,6 @@ func validateB(p *obj.Prog) {
 }
 
 func validateU(p *obj.Prog) {
-	if p.As == AAUIPC && p.Mark&(NEED_PCREL_ITYPE_RELOC|NEED_PCREL_STYPE_RELOC) != 0 {
-		// TODO(sorear): Hack.  The Offset is being used here to temporarily
-		// store the relocation addend, not as an actual offset to assemble,
-		// so it's OK for it to be out of range.  Is there a more valid way
-		// to represent this state?
-		return
-	}
 	wantImmI(p, "from", p.From, 20)
 	wantIntRegAddr(p, "to", &p.To)
 }
@@ -1868,20 +1857,17 @@ func assemble(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				ctxt.Diag("AUIPC needing PC-relative reloc missing following instruction")
 				break
 			}
-			if p.From.Sym == nil {
+			addr := p.RestArgs[0]
+			if addr.Sym == nil {
 				ctxt.Diag("AUIPC needing PC-relative reloc missing symbol")
 				break
 			}
 
-			// The relocation offset can be larger than the maximum
-			// size of an AUIPC, so zero p.From.Offset to avoid any
-			// attempt to assemble it.
 			rel := obj.Addrel(cursym)
 			rel.Off = int32(p.Pc)
 			rel.Siz = 8
-			rel.Sym = p.From.Sym
-			rel.Add = p.From.Offset
-			p.From.Offset = 0
+			rel.Sym = addr.Sym
+			rel.Add = addr.Offset
 			rel.Type = rt
 		}