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cmd/compile,runtime: change unsafe.Slice((*T)(nil), 0) to return []T(nil)

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This CL removes the unconditional OCHECKNIL check added in
walkUnsafeSlice by instead passing it as a pointer to
runtime.unsafeslice, and hiding the check behind a `len == 0` check.

While here, this CL also implements checkptr functionality for
unsafe.Slice and disallows use of unsafe.Slice with //go:notinheap
types.

Updates #46742.

Change-Id: I743a445ac124304a4d7322a7fe089c4a21b9a655
Reviewed-on: https://go-review.googlesource.com/c/go/+/331070
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Matthew Dempsky 2021-06-25 11:07:28 -07:00
parent 1519271a93
commit 4bb0847b08
9 changed files with 83 additions and 27 deletions
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24
src/runtime/slice.go
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@ -112,19 +112,37 @@ func makeslice64(et *_type, len64, cap64 int64) unsafe.Pointer {
return makeslice(et, len, cap)
}
func unsafeslice(et *_type, len int) {
func unsafeslice(et *_type, ptr unsafe.Pointer, len int) {
if len == 0 {
return
}
if ptr == nil {
panic(errorString("unsafe.Slice: ptr is nil and len is not zero"))
}
mem, overflow := math.MulUintptr(et.size, uintptr(len))
if overflow || mem > maxAlloc || len < 0 {
panicunsafeslicelen()
}
}
func unsafeslice64(et *_type, len64 int64) {
func unsafeslice64(et *_type, ptr unsafe.Pointer, len64 int64) {
len := int(len64)
if int64(len) != len64 {
panicunsafeslicelen()
}
unsafeslice(et, len)
unsafeslice(et, ptr, len)
}
func unsafeslicecheckptr(et *_type, ptr unsafe.Pointer, len64 int64) {
unsafeslice64(et, ptr, len64)
// Check that underlying array doesn't straddle multiple heap objects.
// unsafeslice64 has already checked for overflow.
if checkptrStraddles(ptr, uintptr(len64)*et.size) {
throw("checkptr: unsafe.Slice result straddles multiple allocations")
}
}
func panicunsafeslicelen() {