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cmd/compile: reorganize init functions

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Instead of writing an init function per package that does the same
thing for every package, just write that implementation once in the
runtime. Change the compiler to generate a data structure that encodes
the required initialization operations.

Reduces cmd/go binary size by 0.3%+.  Most of the init code is gone,
including all the corresponding stack map info. The .inittask
structures that replace them are quite a bit smaller.

Most usefully to me, there is no longer an init function in every -S output.
(There is an .inittask global there, but it's much less distracting.)

After this CL we could change the name of the "init.ializers" function
back to just "init".

Update #6853

R=go1.13

Change-Id: Iec82b205cc52fe3ade4d36406933c97dbc9c01b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/161337
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
This commit is contained in:
Keith Randall 2019-02-05 16:22:38 -08:00 committed by Keith Randall
parent 991c85a750
commit d949d0b925
8 changed files with 99 additions and 221 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

236
src/cmd/compile/internal/gc/init.go
View File

@ -6,6 +6,7 @@ package gc
import (
"cmd/compile/internal/types"
"cmd/internal/obj"
)
// A function named init is a special case.
@ -23,77 +24,29 @@ func renameinit() *types.Sym {
return s
}
// anyinit reports whether there any interesting init statements.
func anyinit(n []*Node) bool {
for _, ln := range n {
switch ln.Op {
case ODCLFUNC, ODCLCONST, ODCLTYPE, OEMPTY:
case OAS:
if !ln.Left.isBlank() || !candiscard(ln.Right) {
return true
}
default:
return true
}
}
// is this main
if localpkg.Name == "main" {
return true
}
// is there an explicit init function
if renameinitgen > 0 {
return true
}
// are there any imported init functions
for _, s := range types.InitSyms {
if s.Def != nil {
return true
}
}
// then none
return false
}
// fninit hand-crafts package initialization code.
//
// func init.ializers() { (0)
// <init stmts>
// }
// var initdone· uint8 (1)
// func init() { (2)
// if initdone· > 1 { (3)
// return (3a)
// }
// if initdone· == 1 { (4)
// throw() (4a)
// }
// initdone· = 1 (5)
// // over all matching imported symbols
// <pkg>.init() (6)
// init.ializers() (7)
// init.<n>() // if any (8)
// initdone· = 2 (9)
// return (10)
// }
// fninit makes an initialization record for the package.
// See runtime/proc.go:initTask for its layout.
// The 3 tasks for initialization are:
// 1) Initialize all of the packages the current package depends on.
// 2) Initialize all the variables that have initializers.
// 3) Run any init functions.
func fninit(n []*Node) {
lineno = autogeneratedPos
nf := initfix(n)
if !anyinit(nf) {
return
var deps []*obj.LSym // initTask records for packages the current package depends on
var fns []*obj.LSym // functions to call for package initialization
// Find imported packages with init tasks.
for _, p := range types.ImportedPkgList() {
if s, ok := p.LookupOK(".inittask"); ok {
deps = append(deps, s.Linksym())
}
}
// (0)
// Make a function that contains all the initialization statements.
// This is a separate function because we want it to appear in
// stack traces, where the init function itself does not.
var initializers *types.Sym
if len(nf) > 0 {
lineno = nf[0].Pos // prolog/epilog gets line number of first init stmt
initializers = lookup("init.ializers")
initializers := lookup("init.ializers")
disableExport(initializers)
fn := dclfunc(initializers, nod(OTFUNC, nil, nil))
for _, dcl := range dummyInitFn.Func.Dcl {
@ -110,7 +63,7 @@ func fninit(n []*Node) {
typecheckslice(nf, ctxStmt)
Curfn = nil
funccompile(fn)
lineno = autogeneratedPos
fns = append(fns, initializers.Linksym())
}
if dummyInitFn.Func.Dcl != nil {
// We only generate temps using dummyInitFn if there
@ -119,140 +72,37 @@ func fninit(n []*Node) {
Fatalf("dummyInitFn still has declarations")
}
var r []*Node
// (1)
gatevar := newname(lookup("initdone·"))
addvar(gatevar, types.Types[TUINT8], PEXTERN)
// (2)
initsym := lookup("init")
fn := dclfunc(initsym, nod(OTFUNC, nil, nil))
// (3)
a := nod(OIF, nil, nil)
a.Left = nod(OGT, gatevar, nodintconst(1))
a.SetLikely(true)
r = append(r, a)
// (3a)
a.Nbody.Set1(nod(ORETURN, nil, nil))
// (4)
b := nod(OIF, nil, nil)
b.Left = nod(OEQ, gatevar, nodintconst(1))
// this actually isn't likely, but code layout is better
// like this: no JMP needed after the call.
b.SetLikely(true)
r = append(r, b)
// (4a)
b.Nbody.Set1(nod(OCALL, syslook("throwinit"), nil))
// (5)
a = nod(OAS, gatevar, nodintconst(1))
r = append(r, a)
// (6)
for _, s := range types.InitSyms {
if s == initsym {
continue
}
n := resolve(oldname(s))
if n.Op == ONONAME {
// No package-scope init function; just a
// local variable, field name, or something.
continue
}
n.checkInitFuncSignature()
a = nod(OCALL, n, nil)
r = append(r, a)
}
// (7)
if initializers != nil {
n := newname(initializers)
addvar(n, functype(nil, nil, nil), PFUNC)
r = append(r, nod(OCALL, n, nil))
}
// (8)
// maxInlineInitCalls is the threshold at which we switch
// from generating calls inline to generating a static array
// of functions and calling them in a loop.
// See CL 41500 for more discussion.
const maxInlineInitCalls = 500
if renameinitgen < maxInlineInitCalls {
// Not many init functions. Just call them all directly.
// Record user init functions.
for i := 0; i < renameinitgen; i++ {
s := lookupN("init.", i)
n := asNode(s.Def)
n.checkInitFuncSignature()
a = nod(OCALL, n, nil)
r = append(r, a)
}
} else {
// Lots of init functions.
// Set up an array of functions and loop to call them.
// This is faster to compile and similar at runtime.
// Build type [renameinitgen]func().
typ := types.NewArray(functype(nil, nil, nil), int64(renameinitgen))
// Make and fill array.
fnarr := staticname(typ)
fnarr.Name.SetReadonly(true)
for i := 0; i < renameinitgen; i++ {
s := lookupN("init.", i)
lhs := nod(OINDEX, fnarr, nodintconst(int64(i)))
rhs := asNode(s.Def)
rhs.checkInitFuncSignature()
as := nod(OAS, lhs, rhs)
as = typecheck(as, ctxStmt)
genAsStatic(as)
fns = append(fns, s.Linksym())
}
// Generate a loop that calls each function in turn.
// for i := 0; i < renameinitgen; i++ {
// fnarr[i]()
// }
i := temp(types.Types[TINT])
fnidx := nod(OINDEX, fnarr, i)
fnidx.SetBounded(true)
zero := nod(OAS, i, nodintconst(0))
cond := nod(OLT, i, nodintconst(int64(renameinitgen)))
incr := nod(OAS, i, nod(OADD, i, nodintconst(1)))
body := nod(OCALL, fnidx, nil)
loop := nod(OFOR, cond, incr)
loop.Nbody.Set1(body)
loop.Ninit.Set1(zero)
loop = typecheck(loop, ctxStmt)
r = append(r, loop)
if len(deps) == 0 && len(fns) == 0 && localpkg.Name != "main" && localpkg.Name != "runtime" {
return // nothing to initialize
}
// (9)
a = nod(OAS, gatevar, nodintconst(2))
r = append(r, a)
// (10)
a = nod(ORETURN, nil, nil)
r = append(r, a)
exportsym(fn.Func.Nname)
fn.Nbody.Set(r)
funcbody()
Curfn = fn
fn = typecheck(fn, ctxStmt)
typecheckslice(r, ctxStmt)
Curfn = nil
funccompile(fn)
// Make an .inittask structure.
sym := lookup(".inittask")
nn := newname(sym)
nn.Type = types.Types[TUINT8] // dummy type
nn.SetClass(PEXTERN)
sym.Def = asTypesNode(nn)
exportsym(nn)
lsym := sym.Linksym()
ot := 0
ot = duintptr(lsym, ot, 0) // state: not initialized yet
ot = duintptr(lsym, ot, uint64(len(deps)))
ot = duintptr(lsym, ot, uint64(len(fns)))
for _, d := range deps {
ot = dsymptr(lsym, ot, d, 0)
}
for _, f := range fns {
ot = dsymptr(lsym, ot, f, 0)
}
// An initTask has pointers, but none into the Go heap.
// It's not quite read only, the state field must be modifiable.
ggloblsym(lsym, int32(ot), obj.NOPTR)
}
func (n *Node) checkInitFuncSignature() {

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

@ -148,7 +148,7 @@ func relocsym(ctxt *Link, s *sym.Symbol) {
// When putting the runtime but not main into a shared library
// these symbols are undefined and that's OK.
if ctxt.BuildMode == BuildModeShared {
if r.Sym.Name == "main.main" || r.Sym.Name == "main.init" {
if r.Sym.Name == "main.main" || r.Sym.Name == "main..inittask" {
r.Sym.Type = sym.SDYNIMPORT
} else if strings.HasPrefix(r.Sym.Name, "go.info.") {
// Skip go.info symbols. They are only needed to communicate

4
src/cmd/link/internal/ld/deadcode.go
View File

@ -222,7 +222,7 @@ func (d *deadcodepass) init() {
// functions and mark what is reachable from there.
if d.ctxt.linkShared && (d.ctxt.BuildMode == BuildModeExe || d.ctxt.BuildMode == BuildModePIE) {
names = append(names, "main.main", "main.init")
names = append(names, "main.main", "main..inittask")
} else {
// The external linker refers main symbol directly.
if d.ctxt.LinkMode == LinkExternal && (d.ctxt.BuildMode == BuildModeExe || d.ctxt.BuildMode == BuildModePIE) {
@ -234,7 +234,7 @@ func (d *deadcodepass) init() {
}
names = append(names, *flagEntrySymbol)
if d.ctxt.BuildMode == BuildModePlugin {
names = append(names, objabi.PathToPrefix(*flagPluginPath)+".init", objabi.PathToPrefix(*flagPluginPath)+".main", "go.plugin.tabs")
names = append(names, objabi.PathToPrefix(*flagPluginPath)+"..inittask", objabi.PathToPrefix(*flagPluginPath)+".main", "go.plugin.tabs")
// We don't keep the go.plugin.exports symbol,
// but we do keep the symbols it refers to.

16
src/plugin/plugin_dlopen.go
View File

@ -92,15 +92,13 @@ func open(name string) (*Plugin, error) {
plugins[filepath] = p
pluginsMu.Unlock()
initStr := make([]byte, len(pluginpath)+6)
initStr := make([]byte, len(pluginpath)+len("..inittask")+1) // +1 for terminating NUL
copy(initStr, pluginpath)
copy(initStr[len(pluginpath):], ".init")
copy(initStr[len(pluginpath):], "..inittask")
initFuncPC := C.pluginLookup(h, (*C.char)(unsafe.Pointer(&initStr[0])), &cErr)
if initFuncPC != nil {
initFuncP := &initFuncPC
initFunc := *(*func())(unsafe.Pointer(&initFuncP))
initFunc()
initTask := C.pluginLookup(h, (*C.char)(unsafe.Pointer(&initStr[0])), &cErr)
if initTask != nil {
doInit(initTask)
}
// Fill out the value of each plugin symbol.
@ -150,3 +148,7 @@ var (
// lastmoduleinit is defined in package runtime
func lastmoduleinit() (pluginpath string, syms map[string]interface{}, errstr string)
// doInit is defined in package runtime
//go:linkname doInit runtime.doInit
func doInit(t unsafe.Pointer) // t should be a *runtime.initTask

4
src/runtime/panic.go
View File

@ -183,10 +183,6 @@ func panicmem() {
panic(memoryError)
}
func throwinit() {
throw("recursive call during initialization - linker skew")
}
// Create a new deferred function fn with siz bytes of arguments.
// The compiler turns a defer statement into a call to this.
//go:nosplit

48
src/runtime/proc.go
View File

@ -82,11 +82,11 @@ var (
raceprocctx0 uintptr
)
//go:linkname runtime_init runtime.init
func runtime_init()
//go:linkname runtime_inittask runtime..inittask
var runtime_inittask initTask
//go:linkname main_init main.init
func main_init()
//go:linkname main_inittask main..inittask
var main_inittask initTask
// main_init_done is a signal used by cgocallbackg that initialization
// has been completed. It is made before _cgo_notify_runtime_init_done,
@ -144,7 +144,7 @@ func main() {
throw("runtime.main not on m0")
}
runtime_init() // must be before defer
doInit(&runtime_inittask) // must be before defer
if nanotime() == 0 {
throw("nanotime returning zero")
}
@ -184,8 +184,8 @@ func main() {
cgocall(_cgo_notify_runtime_init_done, nil)
}
fn := main_init // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
fn()
doInit(&main_inittask)
close(main_init_done)
needUnlock = false
@ -196,7 +196,7 @@ func main() {
// has a main, but it is not executed.
return
}
fn = main_main // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
fn := main_main // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
fn()
if raceenabled {
racefini()
@ -5185,3 +5185,35 @@ func gcd(a, b uint32) uint32 {
}
return a
}
// An initTask represents the set of initializations that need to be done for a package.
type initTask struct {
// TODO: pack the first 3 fields more tightly?
state uintptr // 0 = uninitialized, 1 = in progress, 2 = done
ndeps uintptr
nfns uintptr
// followed by ndeps instances of an *initTask, one per package depended on
// followed by nfns pcs, one per init function to run
}
func doInit(t *initTask) {
switch t.state {
case 2: // fully initialized
return
case 1: // initialization in progress
throw("recursive call during initialization - linker skew")
default: // not initialized yet
t.state = 1 // initialization in progress
for i := uintptr(0); i < t.ndeps; i++ {
p := add(unsafe.Pointer(t), (3+i)*sys.PtrSize)
t2 := *(**initTask)(p)
doInit(t2)
}
for i := uintptr(0); i < t.nfns; i++ {
p := add(unsafe.Pointer(t), (3+t.ndeps+i)*sys.PtrSize)
f := *(*func())(unsafe.Pointer(&p))
f()
}
t.state = 2 // initialization done
}
}

4
test/fixedbugs/issue29919.dir/a.go
View File

@ -65,8 +65,8 @@ func f() int {
panic("traceback truncated after init.ializers")
}
f, _ = iter.Next()
if f.Function != "runtime.main" {
panic("runtime.main missing")
if !strings.HasPrefix(f.Function, "runtime.") {
panic("runtime. driver missing")
}
return 0

4
test/init.go
View File

@ -9,13 +9,11 @@
package main
import "runtime"
func init() {
}
func main() {
init() // ERROR "undefined.*init"
runtime.init() // ERROR "unexported.*runtime\.init"
runtime.init() // ERROR "undefined.*runtime\.init"
var _ = init // ERROR "undefined.*init"
}