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cmd/compile: remove gc programs from stack frame objects

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This is a two-pronged approach. First, try to keep large objects
off the stack frame. Second, if they do manage to appear anyway,
use straight bitmasks instead of gc programs.

Generally probably a good idea to keep large objects out of stack frames.
But particularly keeping gc programs off the stack simplifies
runtime code a bit.

This CL sets the limit of most stack objects to 131072 bytes (on 64-bit archs).
There can still be large objects if allocated by a late pass, like order, or
they are required to be on the stack, like function arguments.
But the size for the bitmasks for these objects isn't a huge deal,
as we have already have (probably several) bitmasks for the frame
liveness map itself.

Change-Id: I6d2bed0e9aa9ac7499955562c6154f9264061359
Reviewed-on: https://go-review.googlesource.com/c/go/+/542815
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Keith Randall 2023-11-15 13:38:06 -08:00
parent d4b0bd28ee
commit 5a0f2a7a7c
9 changed files with 32794 additions and 279 deletions
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38
src/runtime/stack.go
View file

@ -722,22 +722,12 @@ func adjustframe(frame *stkframe, adjinfo *adjustinfo) {
// we call into morestack.)
continue
}
ptrdata := obj.ptrdata()
gcdata := obj.gcdata()
var s *mspan
if obj.useGCProg() {
// See comments in mgcmark.go:scanstack
s = materializeGCProg(ptrdata, gcdata)
gcdata = (*byte)(unsafe.Pointer(s.startAddr))
}
for i := uintptr(0); i < ptrdata; i += goarch.PtrSize {
if *addb(gcdata, i/(8*goarch.PtrSize))>>(i/goarch.PtrSize&7)&1 != 0 {
ptrBytes, gcData := obj.gcdata()
for i := uintptr(0); i < ptrBytes; i += goarch.PtrSize {
if *addb(gcData, i/(8*goarch.PtrSize))>>(i/goarch.PtrSize&7)&1 != 0 {
adjustpointer(adjinfo, unsafe.Pointer(p+i))
}
}
if s != nil {
dematerializeGCProg(s)
}
}
}
}
@ -1288,24 +1278,14 @@ type stackObjectRecord struct {
// if non-negative, offset from argp
off int32
size int32
_ptrdata int32 // ptrdata, or -ptrdata is GC prog is used
ptrBytes int32
gcdataoff uint32 // offset to gcdata from moduledata.rodata
}
func (r *stackObjectRecord) useGCProg() bool {
return r._ptrdata < 0
}
func (r *stackObjectRecord) ptrdata() uintptr {
x := r._ptrdata
if x < 0 {
return uintptr(-x)
}
return uintptr(x)
}
// gcdata returns pointer map or GC prog of the type.
func (r *stackObjectRecord) gcdata() *byte {
// gcdata returns the number of bytes that contain pointers, and
// a ptr/nonptr bitmask covering those bytes.
// Note that this bitmask might be larger than internal/abi.MaxPtrmaskBytes.
func (r *stackObjectRecord) gcdata() (uintptr, *byte) {
ptr := uintptr(unsafe.Pointer(r))
var mod *moduledata
for datap := &firstmoduledata; datap != nil; datap = datap.next {
@ -1318,7 +1298,7 @@ func (r *stackObjectRecord) gcdata() *byte {
// you may have made a copy of a stackObjectRecord.
// You must use the original pointer.
res := mod.rodata + uintptr(r.gcdataoff)
return (*byte)(unsafe.Pointer(res))
return uintptr(r.ptrBytes), (*byte)(unsafe.Pointer(res))
}
// This is exported as ABI0 via linkname so obj can call it.