diff options
author | Keith Randall <khr@golang.org> | 2020-08-26 14:17:35 -0700 |
---|---|---|
committer | Keith Randall <khr@golang.org> | 2020-09-16 17:26:46 +0000 |
commit | 42b023d7b9cb8229e3035fa3d36bce41a1ef0c43 (patch) | |
tree | 9aab593bbf7bf04bdafe9298280130e0ee21f570 /src/cmd/cgo | |
parent | 4f915911e84819b69329a224d5b646983ac9fed7 (diff) | |
download | go-42b023d7b9cb8229e3035fa3d36bce41a1ef0c43.tar.gz go-42b023d7b9cb8229e3035fa3d36bce41a1ef0c43.zip |
cmd/cgo: use go:notinheap for anonymous structs
They can't reasonably be allocated on the heap. Not a huge deal, but
it has an interesting and useful side effect.
After CL 249917, the compiler and runtime treat pointers to
go:notinheap types as uintptrs instead of real pointers (no write
barrier, not processed during stack scanning, ...). That feature is
exactly what we want for cgo to fix #40954. All the cases we have of
pointers declared in C, but which might actually be filled with
non-pointer data, are of this form (JNI's jobject heirarch, Darwin's
CFType heirarchy, ...).
Fixes #40954
Change-Id: I44a3b9bc2513d4287107e39d0cbbd0efd46a3aae
Reviewed-on: https://go-review.googlesource.com/c/go/+/250940
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Keith Randall <khr@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Diffstat (limited to 'src/cmd/cgo')
-rw-r--r-- | src/cmd/cgo/gcc.go | 15 | ||||
-rw-r--r-- | src/cmd/cgo/main.go | 3 | ||||
-rw-r--r-- | src/cmd/cgo/out.go | 3 |
3 files changed, 20 insertions, 1 deletions
diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go index eb6c1a5c89..730db44990 100644 --- a/src/cmd/cgo/gcc.go +++ b/src/cmd/cgo/gcc.go @@ -2448,6 +2448,18 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ tt := *t tt.C = &TypeRepr{"%s %s", []interface{}{dt.Kind, tag}} tt.Go = c.Ident("struct{}") + if dt.Kind == "struct" { + // We don't know what the representation of this struct is, so don't let + // anyone allocate one on the Go side. As a side effect of this annotation, + // pointers to this type will not be considered pointers in Go. They won't + // get writebarrier-ed or adjusted during a stack copy. This should handle + // all the cases badPointerTypedef used to handle, but hopefully will + // continue to work going forward without any more need for cgo changes. + tt.NotInHeap = true + // TODO: we should probably do the same for unions. Unions can't live + // on the Go heap, right? It currently doesn't work for unions because + // they are defined as a type alias for struct{}, not a defined type. + } typedef[name.Name] = &tt break } @@ -2518,6 +2530,7 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ } t.Go = name t.BadPointer = sub.BadPointer + t.NotInHeap = sub.NotInHeap if unionWithPointer[sub.Go] { unionWithPointer[t.Go] = true } @@ -2528,6 +2541,7 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ tt := *t tt.Go = sub.Go tt.BadPointer = sub.BadPointer + tt.NotInHeap = sub.NotInHeap typedef[name.Name] = &tt } @@ -3026,6 +3040,7 @@ func (c *typeConv) anonymousStructTypedef(dt *dwarf.TypedefType) bool { // non-pointers in this type. // TODO: Currently our best solution is to find these manually and list them as // they come up. A better solution is desired. +// Note: DEPRECATED. There is now a better solution. Search for NotInHeap in this file. func (c *typeConv) badPointerTypedef(dt *dwarf.TypedefType) bool { if c.badCFType(dt) { return true diff --git a/src/cmd/cgo/main.go b/src/cmd/cgo/main.go index 5a7bb3f87b..ef3ed968e4 100644 --- a/src/cmd/cgo/main.go +++ b/src/cmd/cgo/main.go @@ -151,7 +151,8 @@ type Type struct { Go ast.Expr EnumValues map[string]int64 Typedef string - BadPointer bool + BadPointer bool // this pointer type should be represented as a uintptr (deprecated) + NotInHeap bool // this type should have a go:notinheap annotation } // A FuncType collects information about a function type in both the C and Go worlds. diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go index 50d2811f1b..03b8333b10 100644 --- a/src/cmd/cgo/out.go +++ b/src/cmd/cgo/out.go @@ -108,6 +108,9 @@ func (p *Package) writeDefs() { sort.Strings(typedefNames) for _, name := range typedefNames { def := typedef[name] + if def.NotInHeap { + fmt.Fprintf(fgo2, "//go:notinheap\n") + } fmt.Fprintf(fgo2, "type %s ", name) // We don't have source info for these types, so write them out without source info. // Otherwise types would look like: |