Quoting Jani Nikula (2018-10-16 10:59:42) > On Mon, 15 Oct 2018, Stephen Boyd <swboyd@xxxxxxxxxxxx> wrote: > > When I enable UBSAN and compile this driver with clang I get the > > following build error: > > > > drivers/gpu/drm/i915/intel_engine_cs.o: In function `intel_engine_init_execlist': > > drivers/gpu/drm/i915/intel_engine_cs.c:411: undefined reference to `__compiletime_assert_411' > > > > from what I can figure out, the compiler can't optimize > > execlists_num_ports() sufficiently enough at compile time to figure out > > that the 'execlists->port_mask = 1' assignment one line above the > > BUILD_BUG_ON_NOT_POWER_OF_2 check will make execlists_num_ports() return > > 2. Most likely that's because UBSAN is going to check the load inside > > execlists_num_ports() and that check isn't omitted so the optimizer > > can't optimize away the whole function. > > See [1] for a better explanation. > > [1] http://mid.mail-archive.com/20181009171401.14980-1-natechancellor@xxxxxxxxx > > > So let's just change this check to cause a build error when the maximum > > number of ports isn't a power of two. It looks like this is similar to > > what's being checked here so this might work well enough. > > That's not the same thing. I guess I'd go with the below instead, > similar to the check on the next line. I guess both of the checks could > be static on gcc. > > BR, > Jani. > > > diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c > index f27dbe26bcc1..897d5a557d88 100644 > --- a/drivers/gpu/drm/i915/intel_engine_cs.c > +++ b/drivers/gpu/drm/i915/intel_engine_cs.c > @@ -461,12 +461,14 @@ static void intel_engine_init_batch_pool(struct intel_engine_cs *engine) > i915_gem_batch_pool_init(&engine->batch_pool, engine); > } > > +#define IS_POWER_OF_2(n) ((n) != 0 && ((n) & ((n) - 1)) == 0) > + > static void intel_engine_init_execlist(struct intel_engine_cs *engine) > { > struct intel_engine_execlists * const execlists = &engine->execlists; > > execlists->port_mask = 1; > - BUILD_BUG_ON_NOT_POWER_OF_2(execlists_num_ports(execlists)); > + GEM_BUG_ON(!IS_POWER_OF_2(execlists_num_ports(execlists))); That should be happy with is_power_of_2() from log2.h -Chris _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
