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cmd/link: -buildmode=plugin support for linux

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This CL contains several linker changes to support creating plugins.

It collects the exported plugin symbols provided by the compiler and
includes them in the moduledata.

It treats a binary as being dynamically linked if it imports the plugin
package. This lets the dynamic linker de-duplicate symbols.

Change-Id: I099b6f38dda26306eba5c41dbe7862f5a5918d95
Reviewed-on: https://go-review.googlesource.com/27820
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
David Crawshaw 2016-08-25 21:58:45 -04:00
parent 79167bbd9c
commit eced6754c2
20 changed files with 119 additions and 49 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
src/cmd/link/internal/amd64/asm.go
View File

@ -59,7 +59,7 @@ func gentext(ctxt *ld.Link) {
return
}
addmoduledata := ld.Linklookup(ctxt, "runtime.addmoduledata", 0)
if addmoduledata.Type == obj.STEXT {
if addmoduledata.Type == obj.STEXT && ld.Buildmode != ld.BuildmodePlugin {
// we're linking a module containing the runtime -> no need for
// an init function
return
@ -86,6 +86,9 @@ func gentext(ctxt *ld.Link) {
// c: c3 retq
o(0xc3)
ctxt.Textp = append(ctxt.Textp, initfunc)
if ld.Buildmode == ld.BuildmodePlugin {
ctxt.Textp = append(ctxt.Textp, addmoduledata)
}
initarray_entry := ld.Linklookup(ctxt, "go.link.addmoduledatainit", 0)
initarray_entry.Attr |= ld.AttrReachable
initarray_entry.Attr |= ld.AttrLocal

4
src/cmd/link/internal/amd64/obj.go
View File

@ -90,10 +90,6 @@ func archinit(ctxt *ld.Link) {
ld.Linkmode = ld.LinkInternal
}
if ld.Buildmode == ld.BuildmodeCArchive || ld.Buildmode == ld.BuildmodeCShared || ctxt.DynlinkingGo() {
ld.Linkmode = ld.LinkExternal
}
switch ld.Headtype {
default:
if ld.Linkmode == ld.LinkAuto {

5
src/cmd/link/internal/arm/asm.go
View File

@ -63,7 +63,7 @@ func gentext(ctxt *ld.Link) {
return
}
addmoduledata := ld.Linklookup(ctxt, "runtime.addmoduledata", 0)
if addmoduledata.Type == obj.STEXT {
if addmoduledata.Type == obj.STEXT && ld.Buildmode != ld.BuildmodePlugin {
// we're linking a module containing the runtime -> no need for
// an init function
return
@ -96,6 +96,9 @@ func gentext(ctxt *ld.Link) {
rel.Add = 4
ctxt.Textp = append(ctxt.Textp, initfunc)
if ld.Buildmode == ld.BuildmodePlugin {
ctxt.Textp = append(ctxt.Textp, addmoduledata)
}
initarray_entry := ld.Linklookup(ctxt, "go.link.addmoduledatainit", 0)
initarray_entry.Attr |= ld.AttrReachable
initarray_entry.Attr |= ld.AttrLocal

4
src/cmd/link/internal/arm/obj.go
View File

@ -85,10 +85,6 @@ func archinit(ctxt *ld.Link) {
ld.Linkmode = ld.LinkInternal
}
if ld.Buildmode == ld.BuildmodeCArchive || ld.Buildmode == ld.BuildmodeCShared || ctxt.DynlinkingGo() {
ld.Linkmode = ld.LinkExternal
}
switch ld.Headtype {
default:
if ld.Linkmode == ld.LinkAuto {

4
src/cmd/link/internal/arm64/obj.go
View File

@ -103,10 +103,6 @@ func archinit(ctxt *ld.Link) {
break
}
if ld.Buildmode == ld.BuildmodeCShared || ctxt.DynlinkingGo() {
ld.Linkmode = ld.LinkExternal
}
switch ld.Headtype {
default:
ld.Exitf("unknown -H option: %v", ld.Headtype)

2
src/cmd/link/internal/ld/data.go
View File

@ -1367,7 +1367,7 @@ func (ctxt *Link) dodata() {
/* shared library initializer */
switch Buildmode {
case BuildmodeCArchive, BuildmodeCShared, BuildmodeShared:
case BuildmodeCArchive, BuildmodeCShared, BuildmodeShared, BuildmodePlugin:
hasinitarr = true
}
if hasinitarr {

10
src/cmd/link/internal/ld/deadcode.go
View File

@ -243,6 +243,16 @@ func (d *deadcodepass) init() {
names = append(names, *flagEntrySymbol)
if *FlagLinkshared && (Buildmode == BuildmodeExe || Buildmode == BuildmodePIE) {
names = append(names, "main.main", "main.init")
} else if Buildmode == BuildmodePlugin {
pluginInit := d.ctxt.Library[0].Pkg + ".init"
names = append(names, pluginInit, "go.plugin.tabs")
// We don't keep the go.plugin.exports symbol,
// but we do keep the symbols it refers to.
exports := Linkrlookup(d.ctxt, "go.plugin.exports", 0)
for _, r := range exports.R {
d.mark(r.Sym, nil)
}
}
for _, name := range markextra {
names = append(names, name)

2
src/cmd/link/internal/ld/elf.go
View File

@ -1910,7 +1910,7 @@ func (ctxt *Link) doelf() {
/* shared library initializer */
switch Buildmode {
case BuildmodeCArchive, BuildmodeCShared, BuildmodeShared:
case BuildmodeCArchive, BuildmodeCShared, BuildmodeShared, BuildmodePlugin:
hasinitarr = true
}

2
src/cmd/link/internal/ld/go.go
View File

@ -228,7 +228,7 @@ func loadcgo(ctxt *Link, file string, pkg string, p string) {
s = Linklookup(ctxt, local, 0)
switch Buildmode {
case BuildmodeCShared, BuildmodeCArchive:
case BuildmodeCShared, BuildmodeCArchive, BuildmodePlugin:
if s == Linklookup(ctxt, "main", 0) {
continue
}

53
src/cmd/link/internal/ld/lib.go
View File

@ -164,14 +164,18 @@ type Section struct {
// DynlinkingGo returns whether we are producing Go code that can live
// in separate shared libraries linked together at runtime.
func (ctxt *Link) DynlinkingGo() bool {
return Buildmode == BuildmodeShared || *FlagLinkshared
if !ctxt.Loaded {
panic("DynlinkingGo called before all symbols loaded")
}
canUsePlugins := Linkrlookup(ctxt, "plugin.Open", 0) != nil
return Buildmode == BuildmodeShared || *FlagLinkshared || Buildmode == BuildmodePlugin || canUsePlugins
}
// UseRelro returns whether to make use of "read only relocations" aka
// relro.
func UseRelro() bool {
switch Buildmode {
case BuildmodeCArchive, BuildmodeCShared, BuildmodeShared, BuildmodePIE:
case BuildmodeCArchive, BuildmodeCShared, BuildmodeShared, BuildmodePIE, BuildmodePlugin:
return Iself
default:
return *FlagLinkshared
@ -299,16 +303,12 @@ func libinit(ctxt *Link) {
*flagEntrySymbol = fmt.Sprintf("_rt0_%s_%s_lib", obj.GOARCH, obj.GOOS)
case BuildmodeExe, BuildmodePIE:
*flagEntrySymbol = fmt.Sprintf("_rt0_%s_%s", obj.GOARCH, obj.GOOS)
case BuildmodeShared:
// No *flagEntrySymbol for -buildmode=shared
case BuildmodeShared, BuildmodePlugin:
// No *flagEntrySymbol for -buildmode=shared and plugin
default:
ctxt.Diag("unknown *flagEntrySymbol for buildmode %v", Buildmode)
}
}
if !ctxt.DynlinkingGo() {
Linklookup(ctxt, *flagEntrySymbol, 0).Type = obj.SXREF
}
}
func Exitf(format string, a ...interface{}) {
@ -400,7 +400,7 @@ func (ctxt *Link) findLibPath(libname string) string {
func (ctxt *Link) loadlib() {
switch Buildmode {
case BuildmodeCShared:
case BuildmodeCShared, BuildmodePlugin:
s := Linklookup(ctxt, "runtime.islibrary", 0)
s.Attr |= AttrDuplicateOK
Adduint8(ctxt, s, 1)
@ -453,9 +453,14 @@ func (ctxt *Link) loadlib() {
Linkmode = LinkExternal
}
// Force external linking for PIE binaries on systems
// that do not support internal PIE linking.
if Buildmode == BuildmodePIE {
// These build modes depend on the external linker
// to handle some relocations (such as TLS IE) not
// yet supported by the internal linker.
switch Buildmode {
case BuildmodeCArchive, BuildmodeCShared, BuildmodePIE, BuildmodePlugin, BuildmodeShared:
Linkmode = LinkExternal
}
if *FlagLinkshared {
Linkmode = LinkExternal
}
@ -492,7 +497,7 @@ func (ctxt *Link) loadlib() {
if ctxt.Library[i].Shlib != "" {
ldshlibsyms(ctxt, ctxt.Library[i].Shlib)
} else {
if ctxt.DynlinkingGo() {
if Buildmode == BuildmodeShared || *FlagLinkshared {
Exitf("cannot implicitly include runtime/cgo in a shared library")
}
objfile(ctxt, ctxt.Library[i])
@ -531,7 +536,13 @@ func (ctxt *Link) loadlib() {
tlsg.Attr |= AttrReachable
ctxt.Tlsg = tlsg
moduledata := Linklookup(ctxt, "runtime.firstmoduledata", 0)
var moduledata *Symbol
if Buildmode == BuildmodePlugin {
moduledata = Linklookup(ctxt, "local.pluginmoduledata", 0)
moduledata.Attr |= AttrLocal
} else {
moduledata = Linklookup(ctxt, "runtime.firstmoduledata", 0)
}
if moduledata.Type != 0 && moduledata.Type != obj.SDYNIMPORT {
// If the module (toolchain-speak for "executable or shared
// library") we are linking contains the runtime package, it
@ -626,6 +637,8 @@ func (ctxt *Link) loadlib() {
}
// We've loaded all the code now.
ctxt.Loaded = true
// If there are no dynamic libraries needed, gcc disables dynamic linking.
// Because of this, glibc's dynamic ELF loader occasionally (like in version 2.13)
// assumes that a dynamic binary always refers to at least one dynamic library.
@ -642,6 +655,14 @@ func (ctxt *Link) loadlib() {
}
}
if SysArch == sys.Arch386 {
if (Buildmode == BuildmodeCArchive && Iself) || Buildmode == BuildmodeCShared || Buildmode == BuildmodePIE || ctxt.DynlinkingGo() {
got := Linklookup(ctxt, "_GLOBAL_OFFSET_TABLE_", 0)
got.Type = obj.SDYNIMPORT
got.Attr |= AttrReachable
}
}
importcycles()
}
@ -1012,7 +1033,7 @@ func (l *Link) hostlink() {
// non-closeable: a dlclose will do nothing.
argv = append(argv, "-shared", "-Wl,-z,nodelete")
}
case BuildmodeShared:
case BuildmodeShared, BuildmodePlugin:
if UseRelro() {
argv = append(argv, "-Wl,-z,relro")
}
@ -1658,7 +1679,7 @@ func stkcheck(ctxt *Link, up *chain, depth int) int {
// onlyctxt.Diagnose the direct caller.
// TODO(mwhudson): actually think about this.
if depth == 1 && s.Type != obj.SXREF && !ctxt.DynlinkingGo() &&
Buildmode != BuildmodeCArchive && Buildmode != BuildmodePIE && Buildmode != BuildmodeCShared {
Buildmode != BuildmodeCArchive && Buildmode != BuildmodePIE && Buildmode != BuildmodeCShared && Buildmode != BuildmodePlugin {
ctxt.Diag("call to external function %s", s.Name)
}
return -1

2
src/cmd/link/internal/ld/link.go
View File

@ -165,6 +165,8 @@ type Link struct {
Bso *bufio.Writer
Windows int32
Loaded bool // set after all inputs have been loaded as symbols
// Symbol lookup based on name and indexed by version.
Hash []map[string]*Symbol

9
src/cmd/link/internal/ld/main.go
View File

@ -37,6 +37,7 @@ import (
"flag"
"log"
"os"
"path/filepath"
"runtime"
"runtime/pprof"
"strings"
@ -158,7 +159,8 @@ func Main() {
ctxt.Logf("HEADER = -H%d -T0x%x -D0x%x -R0x%x\n", Headtype, uint64(*FlagTextAddr), uint64(*FlagDataAddr), uint32(*FlagRound))
}
if Buildmode == BuildmodeShared {
switch Buildmode {
case BuildmodeShared:
for i := 0; i < flag.NArg(); i++ {
arg := flag.Arg(i)
parts := strings.SplitN(arg, "=", 2)
@ -172,7 +174,10 @@ func Main() {
pkglistfornote = append(pkglistfornote, '\n')
addlibpath(ctxt, "command line", "command line", file, pkgpath, "")
}
} else {
case BuildmodePlugin:
pluginName := strings.TrimSuffix(filepath.Base(flag.Arg(0)), ".a")
addlibpath(ctxt, "command line", "command line", flag.Arg(0), pluginName, "")
default:
addlibpath(ctxt, "command line", "command line", flag.Arg(0), "main", "")
}
ctxt.loadlib()

2
src/cmd/link/internal/ld/objfile.go
View File

@ -585,7 +585,7 @@ func (r *objReader) readSymName() string {
}
r.rdBuf = adjName[:0] // in case 2*n wasn't enough
if r.ctxt.DynlinkingGo() {
if Buildmode == BuildmodeShared || *FlagLinkshared {
// These types are included in the symbol
// table when dynamically linking. To keep
// binary size down, we replace the names

15
src/cmd/link/internal/ld/sym.go
View File

@ -184,6 +184,7 @@ const (
BuildmodeCArchive
BuildmodeCShared
BuildmodeShared
BuildmodePlugin
)
func (mode *BuildMode) Set(s string) error {
@ -234,6 +235,18 @@ func (mode *BuildMode) Set(s string) error {
return badmode()
}
*mode = BuildmodeShared
case "plugin":
switch obj.GOOS {
case "linux":
switch obj.GOARCH {
case "386", "amd64", "arm", "arm64":
default:
return badmode()
}
default:
return badmode()
}
*mode = BuildmodePlugin
}
return nil
}
@ -252,6 +265,8 @@ func (mode *BuildMode) String() string {
return "c-shared"
case BuildmodeShared:
return "shared"
case BuildmodePlugin:
return "plugin"
}
return fmt.Sprintf("BuildMode(%d)", uint8(*mode))
}

16
src/cmd/link/internal/ld/symtab.go
View File

@ -553,6 +553,22 @@ func (ctxt *Link) symtab() {
Addaddr(ctxt, moduledata, Linklookup(ctxt, "runtime.itablink", 0))
adduint(ctxt, moduledata, uint64(nitablinks))
adduint(ctxt, moduledata, uint64(nitablinks))
// The ptab slice
if Buildmode == BuildmodePlugin {
ptab := Linkrlookup(ctxt, "go.plugin.tabs", 0)
ptab.Attr |= AttrReachable
ptab.Attr |= AttrLocal
ptab.Type = obj.SRODATA
nentries := uint64(len(ptab.P) / 8) // sizeof(nameOff) + sizeof(typeOff)
Addaddr(ctxt, moduledata, ptab)
adduint(ctxt, moduledata, nentries)
adduint(ctxt, moduledata, nentries)
} else {
adduint(ctxt, moduledata, 0)
adduint(ctxt, moduledata, 0)
adduint(ctxt, moduledata, 0)
}
if len(ctxt.Shlibs) > 0 {
thismodulename := filepath.Base(*flagOutfile)
switch Buildmode {

4
src/cmd/link/internal/s390x/obj.go
View File

@ -86,10 +86,6 @@ func archinit(ctxt *ld.Link) {
ld.Linkmode = ld.LinkInternal
}
if ld.Buildmode == ld.BuildmodeCArchive || ld.Buildmode == ld.BuildmodeCShared || ctxt.DynlinkingGo() {
ld.Linkmode = ld.LinkExternal
}
switch ld.Headtype {
default:
ld.Exitf("unknown -H option: %v", ld.Headtype)

7
src/cmd/link/internal/x86/asm.go
View File

@ -58,7 +58,7 @@ func gentext(ctxt *ld.Link) {
if !ld.Iself {
return
}
case ld.BuildmodePIE, ld.BuildmodeCShared:
case ld.BuildmodePIE, ld.BuildmodeCShared, ld.BuildmodePlugin:
// We need get_pc_thunk.
default:
return
@ -98,7 +98,7 @@ func gentext(ctxt *ld.Link) {
}
addmoduledata := ld.Linklookup(ctxt, "runtime.addmoduledata", 0)
if addmoduledata.Type == obj.STEXT {
if addmoduledata.Type == obj.STEXT && ld.Buildmode != ld.BuildmodePlugin {
// we're linking a module containing the runtime -> no need for
// an init function
return
@ -152,6 +152,9 @@ func gentext(ctxt *ld.Link) {
o(0xc3)
ctxt.Textp = append(ctxt.Textp, initfunc)
if ld.Buildmode == ld.BuildmodePlugin {
ctxt.Textp = append(ctxt.Textp, addmoduledata)
}
initarray_entry := ld.Linklookup(ctxt, "go.link.addmoduledatainit", 0)
initarray_entry.Attr |= ld.AttrReachable
initarray_entry.Attr |= ld.AttrLocal

7
src/cmd/link/internal/x86/obj.go
View File

@ -85,13 +85,6 @@ func archinit(ctxt *ld.Link) {
ld.Linkmode = ld.LinkInternal
}
if (ld.Buildmode == ld.BuildmodeCArchive && ld.Iself) || ld.Buildmode == ld.BuildmodeCShared || ld.Buildmode == ld.BuildmodePIE || ctxt.DynlinkingGo() {
ld.Linkmode = ld.LinkExternal
got := ld.Linklookup(ctxt, "_GLOBAL_OFFSET_TABLE_", 0)
got.Type = obj.SDYNIMPORT
got.Attr |= ld.AttrReachable
}
switch ld.Headtype {
default:
if ld.Linkmode == ld.LinkAuto {

13
src/runtime/plugin.go Normal file
View File

@ -0,0 +1,13 @@
// 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
// 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
}

2
src/runtime/symtab.go
View File

@ -198,6 +198,8 @@ type moduledata struct {
typelinks []int32 // offsets from types
itablinks []*itab
ptab []ptabEntry
modulename string
modulehashes []modulehash