Messages in this thread | | | Subject | Re: [PATCH] KVM: x86: fix shift out of bounds reported by UBSAN | From | Paolo Bonzini <> | Date | Tue, 22 Dec 2020 23:49:15 +0100 |
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On 22/12/20 19:31, David Laight wrote: >> /* >> * Use 2ULL to incorporate the necessary +1 in the shift; adding +1 in >> * the shift count will overflow SHL's max shift of 63 if s=0 and e=63. >> */ > A comment of the desired output value would be more use. > I think it is: > return 'e-s' ones followed by 's' zeros without shifting by 64. >
What about a mix of the two:
/* * Return 'e-s' ones followed by 's' zeros. Note that the * apparently obvious 1ULL << (e - s + 1) can shift by 64 if * s=0 and e=63, which is undefined behavior. */
Paolo
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