Messages in this thread | | | Date | Fri, 25 Nov 2022 17:17:50 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH 0/1] Slightly relax the type checking done by min() and max(). |
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On Fri, Nov 25, 2022 at 03:00:40PM +0000, David Laight wrote: > The min() and max() defines include a type check to avoid the unexpected > behaviour when a negative value is compared against and unsigned value. > However a lot of code hits this check and uses min_t() to avoid the error. > Many of these are just plain wrong. > > Those casting to u8 or u16 are particularly suspect, eg: > drivers/usb/misc/usb251xb.c:528: > hub->max_current_sp = min_t(u8, property_u32 / 2000, 50); > > This patch does two changes: > - Replace typeof(x) with typeof((x) + 0) to promote char/short to int. > - Add an (int) cast to constants between 0 and MAX_INT so the compiler > doesn't promote the 'other side' of the comparison to an unsinged type. > If this is done the type test is arranged to always succeed. > > The following can also be done (with some lateral thought): > - Allow all comparisons where both types are signed. > - Allow all comparisons where both types are unsigned. > - Allow comparisons where the larger type is signed. > > In addition most of the min_t() calls are there to compare a signed type > (that holds a non-negative value) with an unsigned value. > The definition: > #define min_unsigned(x,y) min((x) + 0u + 0ull, (y) + 0u + 0ull) > will do an unsigned comparision without 'accidentally' masking off > any non-zero high bits. > > With those extra changes there can be a 'duck shoot' on min_t().
You have an issue with your email setup, i.e. you send two independent messages (not a chain). It probably shows that either you don't use `git send-email` for sending patch, or you missed --thread option to it.
-- With Best Regards, Andy Shevchenko
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