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))); GEM_BUG_ON(execlists_num_ports(execlists) > EXECLIST_MAX_PORTS); execlists->queue_priority = INT_MIN; --- > > Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> > Cc: Michal Marek <michal.lkml@xxxxxxxxxxx> > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> > Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_engine_cs.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c > index 217ed3ee1cab..bdf75628ed83 100644 > --- a/drivers/gpu/drm/i915/intel_engine_cs.c > +++ b/drivers/gpu/drm/i915/intel_engine_cs.c > @@ -463,7 +463,7 @@ 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)); > + BUILD_BUG_ON_NOT_POWER_OF_2(EXECLIST_MAX_PORTS); > GEM_BUG_ON(execlists_num_ports(execlists) > EXECLIST_MAX_PORTS); > > execlists->queue_priority = INT_MIN; -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
