runtime: deferproc/deferreturn in Go
LGTM=rsc
R=golang-codereviews, rsc, khr
CC=golang-codereviews
https://golang.org/cl/139900043
diff --git a/src/pkg/runtime/panic.go b/src/pkg/runtime/panic.go
index 9b95f49..1e35561 100644
--- a/src/pkg/runtime/panic.go
+++ b/src/pkg/runtime/panic.go
@@ -4,6 +4,8 @@
package runtime
+import "unsafe"
+
var indexError = error(errorString("index out of range"))
func panicindex() {
@@ -15,3 +17,200 @@
func panicslice() {
panic(sliceError)
}
+
+var divideError = error(errorString("integer divide by zero"))
+
+func panicdivide() {
+ panic(divideError)
+}
+
+func throwreturn() {
+ gothrow("no return at end of a typed function - compiler is broken")
+}
+
+func throwinit() {
+ gothrow("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
+func deferproc(siz int32, fn *funcval) { // arguments of fn follow fn
+ // the arguments of fn are in a perilous state. The stack map
+ // for deferproc does not describe them. So we can't let garbage
+ // collection or stack copying trigger until we've copied them out
+ // to somewhere safe. deferproc_m does that. Until deferproc_m,
+ // we can only call nosplit routines.
+ argp := uintptr(unsafe.Pointer(&fn))
+ argp += unsafe.Sizeof(fn)
+ if GOARCH == "arm" {
+ argp += ptrSize // skip caller's saved link register
+ }
+ mp := acquirem()
+ mp.scalararg[0] = uintptr(siz)
+ mp.ptrarg[0] = unsafe.Pointer(fn)
+ mp.scalararg[1] = argp
+ mp.scalararg[2] = getcallerpc(unsafe.Pointer(&siz))
+
+ if mp.curg != getg() {
+ // go code on the m stack can't defer
+ gothrow("defer on m")
+ }
+
+ onM(deferproc_m)
+
+ releasem(mp)
+
+ // deferproc returns 0 normally.
+ // a deferred func that stops a panic
+ // makes the deferproc return 1.
+ // the code the compiler generates always
+ // checks the return value and jumps to the
+ // end of the function if deferproc returns != 0.
+ return0()
+ // No code can go here - the C return register has
+ // been set and must not be clobbered.
+}
+
+// Each P holds pool for defers with arg sizes 8, 24, 40, 56 and 72 bytes.
+// Memory block is 40 (24 for 32 bits) bytes larger due to Defer header.
+// This maps exactly to malloc size classes.
+
+// defer size class for arg size sz
+func deferclass(siz uintptr) uintptr {
+ return (siz + 7) >> 4
+}
+
+// total size of memory block for defer with arg size sz
+func totaldefersize(siz uintptr) uintptr {
+ return (unsafe.Sizeof(_defer{}) - unsafe.Sizeof(_defer{}.args)) + round(siz, ptrSize)
+}
+
+// Ensure that defer arg sizes that map to the same defer size class
+// also map to the same malloc size class.
+func testdefersizes() {
+ var m [len(p{}.deferpool)]int32
+
+ for i := range m {
+ m[i] = -1
+ }
+ for i := uintptr(0); ; i++ {
+ defersc := deferclass(i)
+ if defersc >= uintptr(len(m)) {
+ break
+ }
+ siz := goroundupsize(totaldefersize(i))
+ if m[defersc] < 0 {
+ m[defersc] = int32(siz)
+ continue
+ }
+ if m[defersc] != int32(siz) {
+ print("bad defer size class: i=", i, " siz=", siz, " defersc=", defersc, "\n")
+ gothrow("bad defer size class")
+ }
+ }
+}
+
+// Allocate a Defer, usually using per-P pool.
+// Each defer must be released with freedefer.
+// Note: runs on M stack
+func newdefer(siz int32) *_defer {
+ var d *_defer
+ sc := deferclass(uintptr(siz))
+ mp := acquirem()
+ if sc < uintptr(len(p{}.deferpool)) {
+ pp := mp.p
+ d = pp.deferpool[sc]
+ if d != nil {
+ pp.deferpool[sc] = d.link
+ }
+ }
+ if d == nil {
+ // deferpool is empty or just a big defer
+ total := goroundupsize(totaldefersize(uintptr(siz)))
+ d = (*_defer)(gomallocgc(total, conservative, 0))
+ }
+ d.siz = siz
+ d.special = false
+ gp := mp.curg
+ d.link = gp._defer
+ gp._defer = d
+ releasem(mp)
+ return d
+}
+
+// Free the given defer.
+// The defer cannot be used after this call.
+func freedefer(d *_defer) {
+ if d.special {
+ return
+ }
+ sc := deferclass(uintptr(d.siz))
+ if sc < uintptr(len(p{}.deferpool)) {
+ mp := acquirem()
+ pp := mp.p
+ d.link = pp.deferpool[sc]
+ pp.deferpool[sc] = d
+ releasem(mp)
+ // No need to wipe out pointers in argp/pc/fn/args,
+ // because we empty the pool before GC.
+ }
+}
+
+// Run a deferred function if there is one.
+// The compiler inserts a call to this at the end of any
+// function which calls defer.
+// If there is a deferred function, this will call runtime·jmpdefer,
+// which will jump to the deferred function such that it appears
+// to have been called by the caller of deferreturn at the point
+// just before deferreturn was called. The effect is that deferreturn
+// is called again and again until there are no more deferred functions.
+// Cannot split the stack because we reuse the caller's frame to
+// call the deferred function.
+
+// The single argument isn't actually used - it just has its address
+// taken so it can be matched against pending defers.
+//go:nosplit
+func deferreturn(arg0 uintptr) {
+ gp := getg()
+ d := gp._defer
+ if d == nil {
+ return
+ }
+ argp := uintptr(unsafe.Pointer(&arg0))
+ if d.argp != argp {
+ return
+ }
+
+ // Moving arguments around.
+ // Do not allow preemption here, because the garbage collector
+ // won't know the form of the arguments until the jmpdefer can
+ // flip the PC over to fn.
+ mp := acquirem()
+ memmove(unsafe.Pointer(argp), unsafe.Pointer(&d.args), uintptr(d.siz))
+ fn := d.fn
+ gp._defer = d.link
+ freedefer(d)
+ releasem(mp)
+ jmpdefer(fn, argp)
+}
+
+// Goexit terminates the goroutine that calls it. No other goroutine is affected.
+// Goexit runs all deferred calls before terminating the goroutine.
+//
+// Calling Goexit from the main goroutine terminates that goroutine
+// without func main returning. Since func main has not returned,
+// the program continues execution of other goroutines.
+// If all other goroutines exit, the program crashes.
+func Goexit() {
+ // Run all deferred functions for the current goroutine.
+ gp := getg()
+ for gp._defer != nil {
+ d := gp._defer
+ gp._defer = d.link
+ reflectcall(unsafe.Pointer(d.fn), unsafe.Pointer(&d.args), uint32(d.siz), uint32(d.siz))
+ freedefer(d)
+ // Note: we ignore recovers here because Goexit isn't a panic
+ }
+ goexit()
+}
