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consensus/ethash: fix usage of *reflect.SliceHeader (#21372)

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* consensus/ethash: only use *reflect.SliceHeader, not reflect.SliceHeader. See comment here: https://github.com/golang/go/issues/40397\#issuecomment-663748689

* consensus/ethash: pr feedback from @mdempsky, makes a copy of dest such that is not mutated

* consensus/ethash: remove noop assign

* consensus/ethash: apply same fix to another location

Co-authored-by: Péter Szilágyi <peterke@gmail.com>
Co-authored-by: Martin Holst Swende <martin@swende.se>
This commit is contained in:
Preston Van Loon 2020-11-17 01:35:58 -08:00 committed by GitHub
parent 1ea7537997
commit 844485ec6a
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 12 additions and 8 deletions
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20
consensus/ethash/algorithm.go
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@ -151,10 +151,12 @@ func generateCache(dest []uint32, epoch uint64, seed []byte) {
logFn("Generated ethash verification cache", "elapsed", common.PrettyDuration(elapsed))
}()
// Convert our destination slice to a byte buffer
header := *(*reflect.SliceHeader)(unsafe.Pointer(&dest))
header.Len *= 4
header.Cap *= 4
cache := *(*[]byte)(unsafe.Pointer(&header))
var cache []byte
cacheHdr := (*reflect.SliceHeader)(unsafe.Pointer(&cache))
dstHdr := (*reflect.SliceHeader)(unsafe.Pointer(&dest))
cacheHdr.Data = dstHdr.Data
cacheHdr.Len = dstHdr.Len * 4
cacheHdr.Cap = dstHdr.Cap * 4
// Calculate the number of theoretical rows (we'll store in one buffer nonetheless)
size := uint64(len(cache))
@ -283,10 +285,12 @@ func generateDataset(dest []uint32, epoch uint64, cache []uint32) {
swapped := !isLittleEndian()
// Convert our destination slice to a byte buffer
header := *(*reflect.SliceHeader)(unsafe.Pointer(&dest))
header.Len *= 4
header.Cap *= 4
dataset := *(*[]byte)(unsafe.Pointer(&header))
var dataset []byte
datasetHdr := (*reflect.SliceHeader)(unsafe.Pointer(&dataset))
destHdr := (*reflect.SliceHeader)(unsafe.Pointer(&dest))
datasetHdr.Data = destHdr.Data
datasetHdr.Len = destHdr.Len * 4
datasetHdr.Cap = destHdr.Cap * 4
// Generate the dataset on many goroutines since it takes a while
threads := runtime.NumCPU()