| Message ID | 20181015203410.155997-1-swboyd@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/i915: Silence build error with UBSAN | expand |
On Mon, 15 Oct 2018, Stephen Boyd <swboyd@chromium.org> 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@gmail.com > 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@socionext.com> > Cc: Michal Marek <michal.lkml@markovi.net> > Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> > Signed-off-by: Stephen Boyd <swboyd@chromium.org> > --- > 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;
Quoting Jani Nikula (2018-10-16 10:59:42) > On Mon, 15 Oct 2018, Stephen Boyd <swboyd@chromium.org> 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@gmail.com > > > 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
On Tue, 16 Oct 2018, Chris Wilson <chris@chris-wilson.co.uk> wrote: > Quoting Jani Nikula (2018-10-16 10:59:42) >> 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 D'oh. Thanks. I was sure there was one, I looked for it, but my git greps were all upper case. :/ I'll spin a new version, along with the other clang build fix. BR, Jani.
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;
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@socionext.com> Cc: Michal Marek <michal.lkml@markovi.net> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Signed-off-by: Stephen Boyd <swboyd@chromium.org> --- drivers/gpu/drm/i915/intel_engine_cs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)