Messages in this thread | | | From | Nick Desaulniers <> | Date | Sat, 23 Dec 2017 22:28:37 -0500 | Subject | Re: [PATCH] zsmalloc: use U suffix for negative literals being shifted |
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On Sat, Dec 23, 2017 at 10:24 PM, Matthew Wilcox <willy@infradead.org> wrote: > On Sat, Dec 23, 2017 at 09:33:40PM -0500, Nick Desaulniers wrote: >> Fixes warnings about shifting unsigned literals being undefined >> behavior. > > Do you mean signed literals?
A sorry, s/unsigned/negative signed/g. The warning is:
mm/zsmalloc.c:1059:20: warning: shifting a negative signed value is undefined [-Wshift-negative-value] link->next = -1 << OBJ_TAG_BITS; ~~ ^
> >> */ >> - link->next = -1 << OBJ_TAG_BITS; >> + link->next = -1U << OBJ_TAG_BITS; >> } > > I don't understand what -1U means. Seems like a contradiction in terms, > a negative unsigned number. Is this supposed to be ~0U?
$ ag \\-1U[^L]
The code base is full of that literal. I think of it as:
(unsigned) -1
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