src/runtime/plugin.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 runtime

import "unsafe"

//go:linkname plugin_lastmoduleinit plugin.lastmoduleinit
func plugin_lastmoduleinit() (path string, syms map[string]interface{}) {
	md := firstmoduledata.next
	if md == nil {
		throw("runtime: no plugin module data")
	}
	for md.next != nil {
		md = md.next
	}
	if md.typemap != nil {
		throw("runtime: plugin already initialized")
	}

	for _, pmd := range activeModules() {
		if pmd.pluginpath == md.pluginpath {
			println("plugin: plugin", md.pluginpath, "already loaded")
			throw("plugin: plugin already loaded")
		}

		if inRange(pmd.text, pmd.etext, md.text, md.etext) ||
			inRange(pmd.bss, pmd.ebss, md.bss, md.ebss) ||
			inRange(pmd.data, pmd.edata, md.data, md.edata) ||
			inRange(pmd.types, pmd.etypes, md.types, md.etypes) {
			println("plugin: new module data overlaps with previous moduledata")
			println("\tpmd.text-etext=", hex(pmd.text), "-", hex(pmd.etext))
			println("\tpmd.bss-ebss=", hex(pmd.bss), "-", hex(pmd.ebss))
			println("\tpmd.data-edata=", hex(pmd.data), "-", hex(pmd.edata))
			println("\tpmd.types-etypes=", hex(pmd.types), "-", hex(pmd.etypes))
			println("\tmd.text-etext=", hex(md.text), "-", hex(md.etext))
			println("\tmd.bss-ebss=", hex(md.bss), "-", hex(md.ebss))
			println("\tmd.data-edata=", hex(md.data), "-", hex(md.edata))
			println("\tmd.types-etypes=", hex(md.types), "-", hex(md.etypes))
			throw("plugin: new module data overlaps with previous moduledata")
		}
	}

	// Initialize the freshly loaded module.
	modulesinit()
	typelinksinit()

	lock(&ifaceLock)
	for _, i := range md.itablinks {
		additab(i, true, false)
	}
	unlock(&ifaceLock)

	// Build a map of symbol names to symbols. Here in the runtime
	// we fill out the first word of the interface, the type. We
	// pass these zero value interfaces to the plugin package,
	// where the symbol value is filled in (usually via cgo).
	//
	// Because functions are handled specially in the plugin package,
	// function symbol names are prefixed here with '.' to avoid
	// a dependency on the reflect package.
	syms = make(map[string]interface{}, len(md.ptab))
	for _, ptab := range md.ptab {
		symName := resolveNameOff(unsafe.Pointer(md.types), ptab.name)
		t := (*_type)(unsafe.Pointer(md.types)).typeOff(ptab.typ)
		var val interface{}
		valp := (*[2]unsafe.Pointer)(unsafe.Pointer(&val))
		(*valp)[0] = unsafe.Pointer(t)

		name := symName.name()
		if t.kind&kindMask == kindFunc {
			name = "." + name
		}
		syms[name] = val
	}
	return md.pluginpath, syms
}

// inRange reports whether v0 or v1 are in the range [r0, r1].
func inRange(r0, r1, v0, v1 uintptr) bool {
	return (v0 >= r0 && v0 <= r1) || (v1 >= r0 && v1 <= r1)
}

// A ptabEntry is generated by the compiler for each exported function
// and global variable in the main package of a plugin. It is used to
// initialize the plugin module's symbol map.
type ptabEntry struct {
	name nameOff
	typ  typeOff
}