all: implement plugin build mode for riscv64

Change-Id: I8d7bbeebbf4a46f2fd8d630b1edbaf79b8ffccc5
Reviewed-on: https://go-review.googlesource.com/c/go/+/420114
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
TryBot-Bypass: Joel Sing <joel@sing.id.au>

3 files changed, 142 insertions, 2 deletions

diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go
index b137c7db79..6199dbbb93 100644
--- a/src/cmd/dist/test.go
+++ b/src/cmd/dist/test.go
@@ -1767,7 +1767,7 @@ func buildModeSupported(compiler, buildmode, goos, goarch string) bool {
 
 	case "plugin":
 		switch platform {
-		case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/loong64", "linux/s390x", "linux/ppc64le",
+		case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/loong64", "linux/riscv64", "linux/s390x", "linux/ppc64le",
 			"android/amd64", "android/386",
 			"darwin/amd64", "darwin/arm64",
 			"freebsd/amd64":
diff --git a/src/cmd/internal/obj/riscv/obj.go b/src/cmd/internal/obj/riscv/obj.go
index 3a4ab556f7..c41d99c0c7 100644
--- a/src/cmd/internal/obj/riscv/obj.go
+++ b/src/cmd/internal/obj/riscv/obj.go
@@ -157,6 +157,127 @@ func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
 			p.From.Offset = 0
 		}
 	}
+
+	if ctxt.Flag_dynlink {
+		rewriteToUseGot(ctxt, p, newprog)
+	}
+}
+
+// Rewrite p, if necessary, to access global data via the global offset table.
+func rewriteToUseGot(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
+	if p.As == obj.ADUFFCOPY || p.As == obj.ADUFFZERO {
+		//     ADUFFxxx $offset
+		// becomes
+		//     MOV runtime.duffxxx@GOT, REG_TMP
+		//     ADD $offset, REG_TMP
+		//     CALL REG_TMP
+		var sym *obj.LSym
+		if p.As == obj.ADUFFCOPY {
+			sym = ctxt.LookupABI("runtime.duffcopy", obj.ABIInternal)
+		} else {
+			sym = ctxt.LookupABI("runtime.duffzero", obj.ABIInternal)
+		}
+		offset := p.To.Offset
+		p.As = AMOV
+		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_TMP
+		p.To.Name = obj.NAME_NONE
+		p.To.Offset = 0
+		p.To.Sym = nil
+
+		p1 := obj.Appendp(p, newprog)
+		p1.As = AADD
+		p1.From.Type = obj.TYPE_CONST
+		p1.From.Offset = offset
+		p1.To.Type = obj.TYPE_REG
+		p1.To.Reg = REG_TMP
+
+		p2 := obj.Appendp(p1, newprog)
+		p2.As = obj.ACALL
+		p2.To.Type = obj.TYPE_REG
+		p2.To.Reg = REG_TMP
+	}
+
+	// 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() {
+		// MOV $sym, Rx becomes MOV sym@GOT, Rx
+		// MOV $sym+<off>, Rx becomes MOV sym@GOT, Rx; ADD <off>, Rx
+		if p.As != AMOV {
+			ctxt.Diag("don't know how to handle TYPE_ADDR in %v with -dynlink", p)
+		}
+		if p.To.Type != obj.TYPE_REG {
+			ctxt.Diag("don't know how to handle LD instruction 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(p, newprog)
+			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.GetFrom3() != nil && p.GetFrom3().Name == obj.NAME_EXTERN {
+		ctxt.Diag("don't know how to handle %v with -dynlink", p)
+	}
+
+	var source *obj.Addr
+	// MOVx sym, Ry becomes MOV sym@GOT, X31; MOVx (X31), Ry
+	// MOVx Ry, sym becomes MOV sym@GOT, X31; MOV Ry, (X31)
+	// 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 == objabi.STLSBSS {
+		return
+	}
+	if source.Type != obj.TYPE_MEM {
+		ctxt.Diag("don't know how to handle %v with -dynlink", p)
+	}
+	p1 := obj.Appendp(p, newprog)
+	p1.As = AMOV
+	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_TMP
+
+	p2 := obj.Appendp(p1, newprog)
+	p2.As = p.As
+	p2.From = p.From
+	p2.To = p.To
+	if p.From.Name == obj.NAME_EXTERN {
+		p2.From.Reg = REG_TMP
+		p2.From.Name = obj.NAME_NONE
+		p2.From.Sym = nil
+	} else if p.To.Name == obj.NAME_EXTERN {
+		p2.To.Reg = REG_TMP
+		p2.To.Name = obj.NAME_NONE
+		p2.To.Sym = nil
+	} else {
+		return
+	}
+	obj.Nopout(p)
+
 }
 
 // addrToReg extracts the register from an Addr, handling special Addr.Names.
diff --git a/src/cmd/link/internal/riscv64/asm.go b/src/cmd/link/internal/riscv64/asm.go
index 8e5d5be41e..527f09e17c 100644
--- a/src/cmd/link/internal/riscv64/asm.go
+++ b/src/cmd/link/internal/riscv64/asm.go
@@ -20,7 +20,26 @@ import (
 // fakeLabelName matches the RISCV_FAKE_LABEL_NAME from binutils.
 const fakeLabelName = ".L0 "
 
-func gentext(ctxt *ld.Link, ldr *loader.Loader) {}
+func gentext(ctxt *ld.Link, ldr *loader.Loader) {
+	initfunc, addmoduledata := ld.PrepareAddmoduledata(ctxt)
+	if initfunc == nil {
+		return
+	}
+
+	// Emit the following function:
+	//
+	// go.link.addmoduledatainit:
+	//      auipc a0, %pcrel_hi(local.moduledata)
+	//      addi  a0, %pcrel_lo(local.moduledata)
+	//      j     runtime.addmoduledata
+
+	sz := initfunc.AddSymRef(ctxt.Arch, ctxt.Moduledata, 0, objabi.R_RISCV_PCREL_ITYPE, 8)
+	initfunc.SetUint32(ctxt.Arch, sz-8, 0x00000517) // auipc a0, %pcrel_hi(local.moduledata)
+	initfunc.SetUint32(ctxt.Arch, sz-4, 0x00050513) // addi  a0, %pcrel_lo(local.moduledata)
+
+	sz = initfunc.AddSymRef(ctxt.Arch, addmoduledata, 0, objabi.R_RISCV_JAL, 4)
+	initfunc.SetUint32(ctxt.Arch, sz-4, 0x0000006f) // j runtime.addmoduledata
+}
 
 func findHI20Reloc(ldr *loader.Loader, s loader.Sym, val int64) *loader.Reloc {
 	outer := ldr.OuterSym(s)