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. 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. 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; -- Sent by a computer through tubes _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
