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

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merged 4 commits into from
Nov 17, 2020
Merged

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

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adb1bce
consensus/ethash: only use *reflect.SliceHeader, not reflect.SliceHea…
prestonvanloon Jul 24, 2020
f3b468f
consensus/ethash: pr feedback from @mdempsky, makes a copy of dest su…
prestonvanloon Jul 24, 2020
c1bf697
consensus/ethash: remove noop assign
karalabe Aug 11, 2020
dc96e44
consensus/ethash: apply same fix to another location
holiman Sep 28, 2020
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4 changes: 2 additions & 2 deletions consensus/ethash/algorithm.go
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Original file line number Diff line number Diff line change
Expand Up @@ -151,10 +151,10 @@ 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 := (*reflect.SliceHeader)(unsafe.Pointer(&dest))
header.Len *= 4
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These statements are going to modify the len and cap of dest, which I don't think you want.

There's also a use of reflect.SliceHeader in ethash/ethash.go.

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What do you recommend is the appropriate fix? I'm not familiar with this bit of code or this usage of reflect.SliceHeader

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var cache []byte
cacheHdr := (*reflect.SliceHeader)(unsafe.Pointer(&cache))
dstHdr := (*reflect.SliceHeader)(unsafe.Pointer(&dst))
cacheHdr.Data = dstHdr.Data
cacheHdr.Len = dstHdr.Len * 4
cacheHdr.Cap = dstHdr.Cap * 4

header.Cap *= 4
cache := *(*[]byte)(unsafe.Pointer(&header))
cache := *(*[]byte)(unsafe.Pointer(header))

// Calculate the number of theoretical rows (we'll store in one buffer nonetheless)
size := uint64(len(cache))
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