On Fri, Mar 6, 2020 at 9:32 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > Variables declared in a switch statement before any case statements > cannot be automatically initialized with compiler instrumentation (as > they are not part of any execution flow). With GCC's proposed automatic > stack variable initialization feature, this triggers a warning (and they > don't get initialized). Clang's automatic stack variable initialization > (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also > doesn't initialize such variables[1]. Note that these warnings (or silent That's not good, have you filed a bug against Clang yet? It should at least warn when the corresponding stack init flag is set. > skipping) happen before the dead-store elimination optimization phase, > so even when the automatic initializations are later elided in favor of > direct initializations, the warnings remain. > > To avoid these problems, lift such variables up into the next code > block. > > drivers/gpu/drm/drm_edid.c: In function ‘drm_edid_to_eld’: > drivers/gpu/drm/drm_edid.c:4395:9: warning: statement will never be > executed [-Wswitch-unreachable] > 4395 | int sad_count; > | ^~~~~~~~~ > > [1] https://bugs.llvm.org/show_bug.cgi?id=44916 > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- > v2: move into function block instead being switch-local (Ville Syrjälä) > --- > drivers/gpu/drm/drm_edid.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c > index 805fb004c8eb..46cee78bc175 100644 > --- a/drivers/gpu/drm/drm_edid.c > +++ b/drivers/gpu/drm/drm_edid.c > @@ -4381,6 +4381,7 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid) > > if (cea_revision(cea) >= 3) { > int i, start, end; > + int sad_count; > > if (cea_db_offsets(cea, &start, &end)) { > start = 0; > @@ -4392,8 +4393,6 @@ static void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid) > dbl = cea_db_payload_len(db); > > switch (cea_db_tag(db)) { > - int sad_count; > - > case AUDIO_BLOCK: > /* Audio Data Block, contains SADs */ > sad_count = min(dbl / 3, 15 - total_sad_count); > -- > 2.20.1 > > > -- > Kees Cook > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/202003060930.DDCCB6659%40keescook. -- Thanks, ~Nick Desaulniers _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
