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cmd/compile: fix possible nil deref added in CL 270943

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In the event allocSpan returned a nil, this would crash.
Cleaned up the code and comments slightly, too.

Change-Id: I6231d4b4c14218e6956b4a97a205adc3206f59ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/316429
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
David Chase 2021-05-03 13:24:27 -04:00
parent 7f9febd4a1
commit 8a4b7294af
1 changed files with 10 additions and 8 deletions
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18
src/runtime/mheap.go
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@ -897,7 +897,8 @@ func (s spanAllocType) manual() bool {
// spanclass indicates the span's size class and scannability.
//
// If needzero is true, the memory for the returned span will be zeroed.
// The boolean returned indicates whether the returned span is zeroed.
// The boolean returned indicates whether the returned span contains zeroes,
// either because this was requested, or because it was already zeroed.
func (h *mheap) alloc(npages uintptr, spanclass spanClass, needzero bool) (*mspan, bool) {
// Don't do any operations that lock the heap on the G stack.
// It might trigger stack growth, and the stack growth code needs
@ -912,14 +913,15 @@ func (h *mheap) alloc(npages uintptr, spanclass spanClass, needzero bool) (*mspa
s = h.allocSpan(npages, spanAllocHeap, spanclass)
})
isZeroed := s.needzero == 0
if s != nil {
if needzero && s.needzero != 0 {
memclrNoHeapPointers(unsafe.Pointer(s.base()), s.npages<<_PageShift)
isZeroed = true
}
s.needzero = 0
if s == nil {
return nil, false
}
isZeroed := s.needzero == 0
if needzero && !isZeroed {
memclrNoHeapPointers(unsafe.Pointer(s.base()), s.npages<<_PageShift)
isZeroed = true
}
s.needzero = 0
return s, isZeroed
}