cmd/internal/obj: flag init functions in object file

Introduce a flag in the object file indicating whether a given
function corresponds to a compiler-generated (not user-written) init
function, such as "os.init" or "syscall.init". Add code to the
compiler to fill in the correct value for the flag, and add support to
the loader package in the linker for testing the flag. The new loader
API is currently unused, but will be needed in the next CL in this
stack.

Updates golang#2559.
Updates golang#36021.
Updates golang#14840.

Change-Id: Iea7ad2adda487e4af7a44f062f9817977c53b394
Reviewed-on: https://go-review.googlesource.com/c/go/+/463855
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

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

@@ -53,6 +53,9 @@ func setupTextLSym(f *Func, flag int) {
 	if f.ReflectMethod() {
 		flag |= obj.REFLECTMETHOD
 	}
+	if f.IsPackageInit() {
+		flag |= obj.PKGINIT
+	}
 
 	// Clumsy but important.
 	// For functions that could be on the path of invoking a deferred

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

@@ -208,6 +208,7 @@ const (
 	funcInstrumentBody           // add race/msan/asan instrumentation during SSA construction
 	funcOpenCodedDeferDisallowed // can't do open-coded defers
 	funcClosureCalled            // closure is only immediately called; used by escape analysis
+	funcPackageInit              // compiler emitted .init func for package
 )
 
 type SymAndPos struct {
@@ -229,6 +230,7 @@ func (f *Func) ExportInline() bool             { return f.flags&funcExportInline
 func (f *Func) InstrumentBody() bool           { return f.flags&funcInstrumentBody != 0 }
 func (f *Func) OpenCodedDeferDisallowed() bool { return f.flags&funcOpenCodedDeferDisallowed != 0 }
 func (f *Func) ClosureCalled() bool            { return f.flags&funcClosureCalled != 0 }
+func (f *Func) IsPackageInit() bool            { return f.flags&funcPackageInit != 0 }
 
 func (f *Func) SetDupok(b bool)                    { f.flags.set(funcDupok, b) }
 func (f *Func) SetWrapper(b bool)                  { f.flags.set(funcWrapper, b) }
@@ -244,6 +246,7 @@ func (f *Func) SetExportInline(b bool)             { f.flags.set(funcExportInlin
 func (f *Func) SetInstrumentBody(b bool)           { f.flags.set(funcInstrumentBody, b) }
 func (f *Func) SetOpenCodedDeferDisallowed(b bool) { f.flags.set(funcOpenCodedDeferDisallowed, b) }
 func (f *Func) SetClosureCalled(b bool)            { f.flags.set(funcClosureCalled, b) }
+func (f *Func) SetIsPackageInit(b bool)            { f.flags.set(funcPackageInit, b) }
 
 func (f *Func) SetWBPos(pos src.XPos) {
 	if base.Debug.WB != 0 {

src/cmd/compile/internal/pkginit/init.go

@@ -36,6 +36,7 @@ func MakeInit() {
 	}
 	fn.Dcl = append(fn.Dcl, typecheck.InitTodoFunc.Dcl...)
 	typecheck.InitTodoFunc.Dcl = nil
+	fn.SetIsPackageInit(true)
 
 	// Suppress useless "can inline" diagnostics.
 	// Init functions are only called dynamically.

src/cmd/internal/goobj/objfile.go

@@ -303,6 +303,7 @@ const (
 	SymFlagUsedInIface = 1 << iota
 	SymFlagItab
 	SymFlagDict
+	SymFlagPkgInit
 )
 
 // Returns the length of the name of the symbol.
@@ -333,6 +334,7 @@ func (s *Sym) IsGoType() bool      { return s.Flag()&SymFlagGoType != 0 }
 func (s *Sym) UsedInIface() bool   { return s.Flag2()&SymFlagUsedInIface != 0 }
 func (s *Sym) IsItab() bool        { return s.Flag2()&SymFlagItab != 0 }
 func (s *Sym) IsDict() bool        { return s.Flag2()&SymFlagDict != 0 }
+func (s *Sym) IsPkgInit() bool     { return s.Flag2()&SymFlagPkgInit != 0 }
 
 func (s *Sym) SetName(x string, w *Writer) {
 	binary.LittleEndian.PutUint32(s[:], uint32(len(x)))

src/cmd/internal/obj/link.go

@@ -796,6 +796,9 @@ const (
 	// IsPcdata indicates this is a pcdata symbol.
 	AttrPcdata
 
+	// PkgInit indicates this is a compiler-generated package init func.
+	AttrPkgInit
+
 	// attrABIBase is the value at which the ABI is encoded in
 	// Attribute. This must be last; all bits after this are
 	// assumed to be an ABI value.
@@ -824,6 +827,7 @@ func (a *Attribute) UsedInIface() bool        { return a.load()&AttrUsedInIface
 func (a *Attribute) ContentAddressable() bool { return a.load()&AttrContentAddressable != 0 }
 func (a *Attribute) ABIWrapper() bool         { return a.load()&AttrABIWrapper != 0 }
 func (a *Attribute) IsPcdata() bool           { return a.load()&AttrPcdata != 0 }
+func (a *Attribute) IsPkgInit() bool          { return a.load()&AttrPkgInit != 0 }
 
 func (a *Attribute) Set(flag Attribute, value bool) {
 	for {
@@ -872,6 +876,7 @@ var textAttrStrings = [...]struct {
 	{bit: AttrIndexed, s: ""},
 	{bit: AttrContentAddressable, s: ""},
 	{bit: AttrABIWrapper, s: "ABIWRAPPER"},
+	{bit: AttrPkgInit, s: "PKGINIT"},
 }
 
 // String formats a for printing in as part of a TEXT prog.

src/cmd/internal/obj/objfile.go

@@ -344,6 +344,9 @@ func (w *writer) Sym(s *LSym) {
 	if strings.HasPrefix(s.Name, w.ctxt.Pkgpath) && strings.HasPrefix(s.Name[len(w.ctxt.Pkgpath):], ".") && strings.HasPrefix(s.Name[len(w.ctxt.Pkgpath)+1:], objabi.GlobalDictPrefix) {
 		flag2 |= goobj.SymFlagDict
 	}
+	if s.IsPkgInit() {
+		flag2 |= goobj.SymFlagPkgInit
+	}
 	name := s.Name
 	if strings.HasPrefix(name, "gofile..") {
 		name = filepath.ToSlash(name)

src/cmd/internal/obj/plist.go

@@ -193,6 +193,7 @@ func (ctxt *Link) InitTextSym(s *LSym, flag int, start src.XPos) {
 	s.Set(AttrABIWrapper, flag&ABIWRAPPER != 0)
 	s.Set(AttrNeedCtxt, flag&NEEDCTXT != 0)
 	s.Set(AttrNoFrame, flag&NOFRAME != 0)
+	s.Set(AttrPkgInit, flag&PKGINIT != 0)
 	s.Type = objabi.STEXT
 	ctxt.Text = append(ctxt.Text, s)
 

src/cmd/internal/obj/textflag.go

@@ -55,4 +55,7 @@ const (
 
 	// Function is an ABI wrapper.
 	ABIWRAPPER = 4096
+
+	// Function is a compiler-generated package init function.
+	PKGINIT = 8192
 )

src/cmd/link/internal/loader/loader.go

@@ -1190,6 +1190,15 @@ func (l *Loader) IsDict(i Sym) bool {
 	return r.Sym(li).IsDict()
 }
 
+// Returns whether this symbol is a compiler-generated package init func.
+func (l *Loader) IsPkgInit(i Sym) bool {
+	if l.IsExternal(i) {
+		return false
+	}
+	r, li := l.toLocal(i)
+	return r.Sym(li).IsPkgInit()
+}
+
 // Return whether this is a trampoline of a deferreturn call.
 func (l *Loader) IsDeferReturnTramp(i Sym) bool {
 	return l.deferReturnTramp[i]