Messages in this thread | | | Date | Tue, 13 Mar 2018 21:01:21 +0100 | From | Luc Van Oostenryck <> | Subject | Re: [tip:locking/core 9/11] include/asm-generic/atomic-instrumented.h:288:24: sparse: cast truncates bits from constant value (100 becomes 0) |
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On Tue, Mar 13, 2018 at 07:08:06PM +0100, Peter Zijlstra wrote: > On Tue, Mar 13, 2018 at 07:00:17PM +0100, Luc Van Oostenryck wrote: > > The issue here is that sparse has a whole class of warnings that are > > given very early (here at expansion of constant expressions), before > > eliminating code from branches that are never taken (which, surprise, > > need itself to have constant expressions already expanded). > > > > It's often annoying like the case here. > > OTOH, I don't think it's always a bad thing. Sometimes we want to > > have warnings even from code we know will not be executed (in this > > config but maybe it will in another one). > > Is that really a valid concern with all the automated randconfig > building going on today?
I don't think so, for the kernel at least. For other uses it may. But don't take me wrongly: I don't want to defend those warnings here, I just want to say that the situation is not totally black & white.
One easy-short-term solution that wouldn't make things ugly would be to use a mask instead of a cast:
static __always_inline unsigned long cmpxchg_size(volatile void *ptr, unsigned long old, unsigned long new, int size) { switch (size) { case 1: - return arch_cmpxchg((u8 *)ptr, (u8)old, (u8)new); + return arch_cmpxchg((u8 *)ptr, old & 0xff, new & 0xff); case 2: - return arch_cmpxchg((u16 *)ptr, (u16)old, (u16)new); + return arch_cmpxchg((u16 *)ptr, old & 0xffff, new & 0xffff);
-- Luc
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