Messages in this thread | | | Subject | Re: [PATCH 02/18] arm64: move SCTLR_EL{1,2} assertions to <asm/sysreg.h> | From | Robin Murphy <> | Date | Mon, 14 May 2018 12:56:09 +0100 |
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On 14/05/18 12:20, Dave Martin wrote: > On Mon, May 14, 2018 at 11:08:59AM +0100, Mark Rutland wrote: >> On Mon, May 14, 2018 at 11:00:53AM +0100, Dave Martin wrote: >>> On Mon, May 14, 2018 at 10:46:24AM +0100, Mark Rutland wrote: >>>> -/* Check all the bits are accounted for */ >>>> -#define SCTLR_EL2_BUILD_BUG_ON_MISSING_BITS BUILD_BUG_ON((SCTLR_EL2_SET ^ SCTLR_EL2_CLEAR) != ~0) >>>> - >>>> +#if (SCTLR_EL2_SET ^ SCTLR_EL2_CLEAR) != 0xffffffff >>>> +#error "Inconsistent SCTLR_EL2 set/clear bits" >>>> +#endif >>> >>> Can we have a comment on the != 0xffffffff versus != ~0 here? >>> >>> The subtle differences in evaluation semantics between #if and >>> other contexts here may well trip people up during maintenance... >> >> Do you have any suggestion as to the wording? >> >> I'm happy to add a comment, but I don't really know what to say. > > > How about the following? > > /* Watch out for #if evaluation rules: ~0 is not ~(int)0! */
Or, more formally, perhaps something even less vague like "Note that in preprocessor arithmetic these constants are effectively of type intmax_t, which is 64-bit, thus ~0 is not what we want."
Robin.
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