On Wed, 19 Feb 2020, Kees Cook <keesc...@chromium.org> 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
> 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, move such variables into the "case" where
> they're used or lift them up into the main function body.
>
> drivers/gpu/drm/i915/display/intel_display.c: In function
> ‘check_digital_port_conflicts’:
> drivers/gpu/drm/i915/display/intel_display.c:12963:17: warning: statement
> will never be executed [-Wswitch-unreachable]
> 12963 | unsigned int port_mask;
> | ^~~~~~~~~
>
> drivers/gpu/drm/i915/intel_pm.c: In function ‘vlv_get_fifo_size’:
> drivers/gpu/drm/i915/intel_pm.c:474:7: warning: statement will never be
> executed [-Wswitch-unreachable]
> 474 | u32 dsparb, dsparb2, dsparb3;
> | ^~~~~~
> drivers/gpu/drm/i915/intel_pm.c: In function ‘vlv_atomic_update_fifo’:
> drivers/gpu/drm/i915/intel_pm.c:1997:7: warning: statement will never be
> executed [-Wswitch-unreachable]
> 1997 | u32 dsparb, dsparb2, dsparb3;
> | ^~~~~~
>
> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
>
> Signed-off-by: Kees Cook <keesc...@chromium.org>
Reviewed-by: Jani Nikula <jani.nik...@intel.com>
If you look at i915/Makefile, you'll see that we don't shy away from
enabling lots of extra warnings, and we run our CI with -Werror to keep
it clean. It does not seem like -Wswitch-unreachable does me any good,
though... is it new?
BR,
Jani.
> ---
> drivers/gpu/drm/i915/display/intel_display.c | 6 ++++--
> drivers/gpu/drm/i915/intel_pm.c | 4 ++--
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c
> b/drivers/gpu/drm/i915/display/intel_display.c
> index 064dd99bbc49..c829cd26f99e 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -12960,14 +12960,15 @@ static bool check_digital_port_conflicts(struct
> intel_atomic_state *state)
> WARN_ON(!connector_state->crtc);
>
> switch (encoder->type) {
> - unsigned int port_mask;
> case INTEL_OUTPUT_DDI:
> if (WARN_ON(!HAS_DDI(to_i915(dev))))
> break;
> /* else, fall through */
> case INTEL_OUTPUT_DP:
> case INTEL_OUTPUT_HDMI:
> - case INTEL_OUTPUT_EDP:
> + case INTEL_OUTPUT_EDP: {
> + unsigned int port_mask;
> +
> port_mask = 1 << encoder->port;
>
> /* the same port mustn't appear more than once */
> @@ -12976,6 +12977,7 @@ static bool check_digital_port_conflicts(struct
> intel_atomic_state *state)
>
> used_ports |= port_mask;
> break;
> + }
> case INTEL_OUTPUT_DP_MST:
> used_mst_ports |=
> 1 << encoder->port;
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index bd2d30ecc030..17d8833787c4 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -469,9 +469,9 @@ static void vlv_get_fifo_size(struct intel_crtc_state
> *crtc_state)
> struct vlv_fifo_state *fifo_state = &crtc_state->wm.vlv.fifo_state;
> enum pipe pipe = crtc->pipe;
> int sprite0_start, sprite1_start;
> + u32 dsparb, dsparb2, dsparb3;
>
> switch (pipe) {
> - u32 dsparb, dsparb2, dsparb3;
> case PIPE_A:
> dsparb = I915_READ(DSPARB);
> dsparb2 = I915_READ(DSPARB2);
> @@ -1969,6 +1969,7 @@ static void vlv_atomic_update_fifo(struct
> intel_atomic_state *state,
> const struct vlv_fifo_state *fifo_state =
> &crtc_state->wm.vlv.fifo_state;
> int sprite0_start, sprite1_start, fifo_size;
> + u32 dsparb, dsparb2, dsparb3;
>
> if (!crtc_state->fifo_changed)
> return;
> @@ -1994,7 +1995,6 @@ static void vlv_atomic_update_fifo(struct
> intel_atomic_state *state,
> spin_lock(&uncore->lock);
>
> switch (crtc->pipe) {
> - u32 dsparb, dsparb2, dsparb3;
> case PIPE_A:
> dsparb = intel_uncore_read_fw(uncore, DSPARB);
> dsparb2 = intel_uncore_read_fw(uncore, DSPARB2);
>
--
Jani Nikula, Intel Open Source Graphics Center
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