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runtime: restore old mp.fastrand initialization

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CL 337350 changed mp.fastrand from a [2]uint32 to a uint64 and changed
the initialization to a single call of int64Hash. However, int64Hash
returns uintptr, so 32-bit systems this always left the most
significant 32 bits of mp.fastrand initialized to 0. The new code also
did not protect against initializing mp.fastrand to 0, which on a
system that does not implement math.Mul64 (most 32-bit systems) would
lead fastrand to always return 0.

This CL restores the mp.fastrand initialization to what it was before
CL 337350, adjusted for the change from [2]uint32 to uint64.

Change-Id: I663b415d9424d967e8e665ce2d017604dcd5b204
Reviewed-on: https://go-review.googlesource.com/c/go/+/383916
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Ian Lance Taylor 2022-02-07 17:07:44 -08:00
parent 540632841e
commit 5442f4d51b
1 changed files with 12 additions and 2 deletions
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14
src/runtime/proc.go
View file

@ -802,8 +802,18 @@ func mcommoninit(mp *m, id int64) {
mp.id = mReserveID()
}
// cputicks is not very random in startup virtual machine
mp.fastrand = uint64(int64Hash(uint64(mp.id), fastrandseed^uintptr(cputicks())))
lo := uint32(int64Hash(uint64(mp.id), fastrandseed))
hi := uint32(int64Hash(uint64(cputicks()), ^fastrandseed))
if lo|hi == 0 {
hi = 1
}
// Same behavior as for 1.17.
// TODO: Simplify ths.
if goarch.BigEndian {
mp.fastrand = uint64(lo)<<32 | uint64(hi)
} else {
mp.fastrand = uint64(hi)<<32 | uint64(lo)
}
mpreinit(mp)
if mp.gsignal != nil {