src/cmd/link/internal/ld/typelink.go

// Copyright 2016 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 ld

import (
	"cmd/internal/objabi"
	"cmd/link/internal/loader"
	"cmd/link/internal/sym"
	"slices"
	"strings"
)

type typelinkSortKey struct {
	TypeStr string
	Type    loader.Sym
}

// typelink generates the typelink table which is used by reflect.typelinks().
// Types that should be added to the typelinks table are marked with the
// MakeTypelink attribute by the compiler.
func (ctxt *Link) typelink() {
	ldr := ctxt.loader
	var typelinks []typelinkSortKey
	var itabs []loader.Sym
	for s := loader.Sym(1); s < loader.Sym(ldr.NSym()); s++ {
		if !ldr.AttrReachable(s) {
			continue
		}
		if ldr.IsTypelink(s) {
			typelinks = append(typelinks, typelinkSortKey{decodetypeStr(ldr, ctxt.Arch, s), s})
		} else if ldr.IsItab(s) {
			itabs = append(itabs, s)
		}
	}
	slices.SortFunc(typelinks, func(a, b typelinkSortKey) int {
		return strings.Compare(a.TypeStr, b.TypeStr)
	})

	tl := ldr.CreateSymForUpdate("runtime.typelink", 0)
	tl.SetType(sym.STYPELINK)
	ldr.SetAttrLocal(tl.Sym(), true)
	tl.SetSize(int64(4 * len(typelinks)))
	tl.Grow(tl.Size())
	relocs := tl.AddRelocs(len(typelinks))
	for i, s := range typelinks {
		r := relocs.At(i)
		r.SetSym(s.Type)
		r.SetOff(int32(i * 4))
		r.SetSiz(4)
		r.SetType(objabi.R_ADDROFF)
	}

	ptrsize := ctxt.Arch.PtrSize
	il := ldr.CreateSymForUpdate("runtime.itablink", 0)
	il.SetType(sym.SITABLINK)
	ldr.SetAttrLocal(il.Sym(), true)
	il.SetSize(int64(ptrsize * len(itabs)))
	il.Grow(il.Size())
	relocs = il.AddRelocs(len(itabs))
	for i, s := range itabs {
		r := relocs.At(i)
		r.SetSym(s)
		r.SetOff(int32(i * ptrsize))
		r.SetSiz(uint8(ptrsize))
		r.SetType(objabi.R_ADDR)
	}
}