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cmd/cgo: use go:notinheap for anonymous structs

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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>
This commit is contained in:
Keith Randall 2020-08-26 14:17:35 -07:00
parent 4f915911e8
commit 42b023d7b9
4 changed files with 55 additions and 1 deletions
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3
src/cmd/cgo/out.go
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@ -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: