On Mon, 30 May 2016, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > On Mon, May 30, 2016 at 11:32:59AM +0100, David Binderman wrote: >> Hello there, >> >> drivers/gpu/drm/i915/i915_reg.h:90:28: warning: result of ‘65535 << >> 20’ requires 37 bits to represent, but ‘int’ only has 32 bits >> [-Wshift-overflow=] >> >> Source code is >> >> #define BSM_MASK (0xFFFF << 20) >> >> Maybe better code >> >> #define BSM_MASK (((unsigned long) 0xFFFF) << 20) > > #define BSM_MASK (~0u << 20) > > It should be a 32bit mask. The current (with the exception of undefined > behaviour of shifting into the signbit, fortunately gcc does what we > expect) code is functionally current as the mask will be truncated to > 32bits. In the patch I used BSM_MASK (0xFFF << 20). It does have the UB of shifting into the sign bit, but then we have loads of e.g. (1 << 31) in i915_reg.h which is no different. The original code before e10fa551ae37b had ~((1<<20) - 1). BR, Jani. -- Jani Nikula, Intel Open Source Technology Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
