Messages in this thread | | | Date | Mon, 31 Oct 2022 13:32:40 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86/cpu: fix undefined behavior in bit shift for intel_detect_tlb |
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On Mon, Oct 31, 2022 at 01:30:57PM +0100, Peter Zijlstra wrote: > On Mon, Oct 31, 2022 at 07:43:40PM +0800, Gaosheng Cui wrote: > > Shifting signed 32-bit value by 31 bits is undefined, so changing > > significant bit to unsigned. The UBSAN warning calltrace like below: > > > > UBSAN: shift-out-of-bounds in arch/x86/kernel/cpu/intel.c:948:21 > > left shift of 1 by 31 places cannot be represented in type 'int' > > Is it really? Shouldn't -fstrict-overflow define this case?
-fno-strict-overflow that is, which implies -fwrapv which ensures 2s complement, at which point shifting signed numbers is fully defined.
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