[dev.regabi] cmd/compile: refactor Linksym creation

Currently there's a lot of logic within package types for creating
Linksyms. This CL pulls it out into base, where it can be more easily
reused by other compiler code that shouldn't need to depend on package
types.

Package base probably isn't the best place for this, but it's
convenient because it's a package that types already depends on. It's
also where the Ctxt object lives, which these functions depend upon.

Passes toolstash -cmp w/ -gcflags=all=-abiwrap.

Change-Id: I50d8b7e4596955205036969eab24d7dab053b363
Reviewed-on: https://go-review.googlesource.com/c/go/+/284231
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/base/base.go

@@ -6,12 +6,8 @@ package base
 
 import (
 	"os"
-
-	"cmd/internal/obj"
 )
 
-var Ctxt *obj.Link
-
 var atExitFuncs []func()
 
 func AtExit(f func()) {

src/cmd/compile/internal/base/link.go

@@ -0,0 +1,36 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package base
+
+import (
+	"cmd/internal/obj"
+)
+
+var Ctxt *obj.Link
+
+// TODO(mdempsky): These should probably be obj.Link methods.
+
+// PkgLinksym returns the linker symbol for name within the given
+// package prefix. For user packages, prefix should be the package
+// path encoded with objabi.PathToPrefix.
+func PkgLinksym(prefix, name string, abi obj.ABI) *obj.LSym {
+	if name == "_" {
+		// TODO(mdempsky): Cleanup callers and Fatalf instead.
+		return linksym(prefix, "_", abi)
+	}
+	return linksym(prefix, prefix+"."+name, abi)
+}
+
+// Linkname returns the linker symbol for the given name as it might
+// appear within a //go:linkname directive.
+func Linkname(name string, abi obj.ABI) *obj.LSym {
+	return linksym("_", name, abi)
+}
+
+// linksym is an internal helper function for implementing the above
+// exported APIs.
+func linksym(pkg, name string, abi obj.ABI) *obj.LSym {
+	return Ctxt.LookupABIInit(name, abi, func(r *obj.LSym) { r.Pkg = pkg })
+}

src/cmd/compile/internal/dwarfgen/dwarf.go

@@ -28,7 +28,7 @@ func Info(fnsym *obj.LSym, infosym *obj.LSym, curfn interface{}) ([]dwarf.Scope,
 	if fn.Nname != nil {
 		expect := fn.Linksym()
 		if fnsym.ABI() == obj.ABI0 {
-			expect = fn.Sym().LinksymABI0()
+			expect = fn.LinksymABI(obj.ABI0)
 		}
 		if fnsym != expect {
 			base.Fatalf("unexpected fnsym: %v != %v", fnsym, expect)

src/cmd/compile/internal/ir/func.go

@@ -133,9 +133,10 @@ func (n *Func) copy() Node                         { panic(n.no("copy")) }
 func (n *Func) doChildren(do func(Node) bool) bool { return doNodes(n.Body, do) }
 func (n *Func) editChildren(edit func(Node) Node)  { editNodes(n.Body, edit) }
 
-func (f *Func) Type() *types.Type  { return f.Nname.Type() }
-func (f *Func) Sym() *types.Sym    { return f.Nname.Sym() }
-func (f *Func) Linksym() *obj.LSym { return f.Nname.Linksym() }
+func (f *Func) Type() *types.Type                { return f.Nname.Type() }
+func (f *Func) Sym() *types.Sym                  { return f.Nname.Sym() }
+func (f *Func) Linksym() *obj.LSym               { return f.Nname.Linksym() }
+func (f *Func) LinksymABI(abi obj.ABI) *obj.LSym { return f.Nname.LinksymABI(abi) }
 
 // An Inline holds fields used for function bodies that can be inlined.
 type Inline struct {

src/cmd/compile/internal/ir/name.go

@@ -226,7 +226,8 @@ func (n *Name) SetWalkdef(x uint8) {
 	n.bits.set2(miniWalkdefShift, x)
 }
 
-func (n *Name) Linksym() *obj.LSym { return n.sym.Linksym() }
+func (n *Name) Linksym() *obj.LSym               { return n.sym.Linksym() }
+func (n *Name) LinksymABI(abi obj.ABI) *obj.LSym { return n.sym.LinksymABI(abi) }
 
 func (*Name) CanBeNtype()    {}
 func (*Name) CanBeAnSSASym() {}

src/cmd/compile/internal/ssagen/abi.go

@@ -161,11 +161,11 @@ func selectLSym(f *ir.Func, hasBody bool) {
 
 		var wrapperABI obj.ABI
 		needABIWrapper := false
-		defABI, hasDefABI := symabiDefs[nam.Sym().LinksymName()]
+		defABI, hasDefABI := symabiDefs[nam.Linksym().Name]
 		if hasDefABI && defABI == obj.ABI0 {
 			// Symbol is defined as ABI0. Create an
 			// Internal -> ABI0 wrapper.
-			f.LSym = nam.Sym().LinksymABI0()
+			f.LSym = nam.LinksymABI(obj.ABI0)
 			needABIWrapper, wrapperABI = true, obj.ABIInternal
 		} else {
 			f.LSym = nam.Linksym()

src/cmd/compile/internal/ssagen/ssa.go

@@ -7403,9 +7403,9 @@ func callTargetLSym(callee *ir.Name, callerLSym *obj.LSym) *obj.LSym {
 		}
 	} else {
 		// check for case 2 above
-		defABI, hasDefABI := symabiDefs[callee.Sym().LinksymName()]
+		defABI, hasDefABI := symabiDefs[lsym.Name]
 		if hasDefABI && defABI == obj.ABI0 {
-			lsym = callee.Sym().LinksymABI0()
+			lsym = callee.LinksymABI(obj.ABI0)
 		}
 	}
 	return lsym

src/cmd/compile/internal/staticdata/data.go

@@ -287,7 +287,7 @@ func NeedFuncSym(s *types.Sym) {
 
 func WriteFuncSyms() {
 	sort.Slice(funcsyms, func(i, j int) bool {
-		return funcsyms[i].LinksymName() < funcsyms[j].LinksymName()
+		return funcsyms[i].Linksym().Name < funcsyms[j].Linksym().Name
 	})
 	for _, s := range funcsyms {
 		sf := s.Pkg.Lookup(ir.FuncSymName(s)).Linksym()

src/cmd/compile/internal/typecheck/syms.go

@@ -86,14 +86,17 @@ func InitRuntime() {
 // LookupRuntimeFunc looks up Go function name in package runtime. This function
 // must follow the internal calling convention.
 func LookupRuntimeFunc(name string) *obj.LSym {
-	s := ir.Pkgs.Runtime.Lookup(name)
-	s.SetFunc(true)
-	return s.Linksym()
+	return LookupRuntimeABI(name, obj.ABIInternal)
 }
 
 // LookupRuntimeVar looks up a variable (or assembly function) name in package
 // runtime. If this is a function, it may have a special calling
 // convention.
 func LookupRuntimeVar(name string) *obj.LSym {
-	return ir.Pkgs.Runtime.Lookup(name).Linksym()
+	return LookupRuntimeABI(name, obj.ABI0)
+}
+
+// LookupRuntimeABI looks up a name in package runtime using the given ABI.
+func LookupRuntimeABI(name string, abi obj.ABI) *obj.LSym {
+	return base.PkgLinksym("runtime", name, abi)
 }

src/cmd/compile/internal/types/sym.go

@@ -64,53 +64,30 @@ func (sym *Sym) IsBlank() bool {
 	return sym != nil && sym.Name == "_"
 }
 
-func (sym *Sym) LinksymName() string {
-	if sym.IsBlank() {
-		return "_"
-	}
-	if sym.Linkname != "" {
-		return sym.Linkname
-	}
-	return sym.Pkg.Prefix + "." + sym.Name
-}
-
 // Deprecated: This method should not be used directly. Instead, use a
 // higher-level abstraction that directly returns the linker symbol
 // for a named object. For example, reflectdata.TypeLinksym(t) instead
 // of reflectdata.TypeSym(t).Linksym().
 func (sym *Sym) Linksym() *obj.LSym {
-	if sym == nil {
-		return nil
-	}
-	initPkg := func(r *obj.LSym) {
-		if sym.Linkname != "" {
-			r.Pkg = "_"
-		} else {
-			r.Pkg = sym.Pkg.Prefix
-		}
-	}
+	abi := obj.ABI0
 	if sym.Func() {
-		// This is a function symbol. Mark it as "internal ABI".
-		return base.Ctxt.LookupABIInit(sym.LinksymName(), obj.ABIInternal, initPkg)
+		abi = obj.ABIInternal
 	}
-	return base.Ctxt.LookupInit(sym.LinksymName(), initPkg)
+	return sym.LinksymABI(abi)
 }
 
-// LinksymABI0 looks up or creates an ABI0 linker symbol for "sym",
-// in cases where we want to specifically select the ABI0 version of
-// a symbol (typically used only for ABI wrappers).
-func (sym *Sym) LinksymABI0() *obj.LSym {
+// Deprecated: This method should not be used directly. Instead, use a
+// higher-level abstraction that directly returns the linker symbol
+// for a named object. For example, (*ir.Name).LinksymABI(abi) instead
+// of (*ir.Name).Sym().LinksymABI(abi).
+func (sym *Sym) LinksymABI(abi obj.ABI) *obj.LSym {
 	if sym == nil {
-		return nil
+		base.Fatalf("nil symbol")
 	}
-	initPkg := func(r *obj.LSym) {
-		if sym.Linkname != "" {
-			r.Pkg = "_"
-		} else {
-			r.Pkg = sym.Pkg.Prefix
-		}
+	if sym.Linkname != "" {
+		return base.Linkname(sym.Linkname, abi)
 	}
-	return base.Ctxt.LookupABIInit(sym.LinksymName(), obj.ABI0, initPkg)
+	return base.PkgLinksym(sym.Pkg.Prefix, sym.Name, abi)
 }
 
 // Less reports whether symbol a is ordered before symbol b.