From: Arnd Bergmann <[email protected]>
Marking a case of the switch statement as unreachable means the
compiler treats it as undefined behavior, which is then caught by
an objtool warning:
drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.o: warning: objtool: csiphy_lanes_enable() falls through to next function csiphy_lanes_disable()
Instead of simply continuing execution at a random place of the
driver, print a warning and return from to the caller, which
makes it possible to understand what happens and avoids the
warning.
Fixes: 53655d2a0ff2 ("media: camss: csiphy-3ph: add support for SM8250 CSI DPHY")
Signed-off-by: Arnd Bergmann <[email protected]>
---
drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
index 451a4c9b3d30..04baa80494c6 100644
--- a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
+++ b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
@@ -429,7 +429,8 @@ static void csiphy_gen2_config_lanes(struct csiphy_device *csiphy,
array_size = ARRAY_SIZE(lane_regs_sm8250[0]);
break;
default:
- unreachable();
+ WARN(1, "unknown cspi version\n");
+ return;
}
for (l = 0; l < 5; l++) {
--
2.35.1
On Thu, Dec 15, 2022 at 05:28:46PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <[email protected]>
>
> Marking a case of the switch statement as unreachable means the
> compiler treats it as undefined behavior, which is then caught by
> an objtool warning:
>
> drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.o: warning: objtool: csiphy_lanes_enable() falls through to next function csiphy_lanes_disable()
>
> Instead of simply continuing execution at a random place of the
> driver, print a warning and return from to the caller, which
> makes it possible to understand what happens and avoids the
> warning.
>
> Fixes: 53655d2a0ff2 ("media: camss: csiphy-3ph: add support for SM8250 CSI DPHY")
> Signed-off-by: Arnd Bergmann <[email protected]>
> ---
> drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> index 451a4c9b3d30..04baa80494c6 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> @@ -429,7 +429,8 @@ static void csiphy_gen2_config_lanes(struct csiphy_device *csiphy,
> array_size = ARRAY_SIZE(lane_regs_sm8250[0]);
> break;
> default:
> - unreachable();
> + WARN(1, "unknown cspi version\n");
> + return;
> }
So no real objection here; but unreachable() does have an objtool
annotation inside, so clearly the compiler managed to defeat that --
perhaps we should look at that too.
On Thu, 15 Dec 2022 at 17:29, Arnd Bergmann <[email protected]> wrote:
>
> From: Arnd Bergmann <[email protected]>
>
> Marking a case of the switch statement as unreachable means the
> compiler treats it as undefined behavior, which is then caught by
> an objtool warning:
>
> drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.o: warning: objtool: csiphy_lanes_enable() falls through to next function csiphy_lanes_disable()
>
> Instead of simply continuing execution at a random place of the
> driver, print a warning and return from to the caller, which
> makes it possible to understand what happens and avoids the
> warning.
>
> Fixes: 53655d2a0ff2 ("media: camss: csiphy-3ph: add support for SM8250 CSI DPHY")
> Signed-off-by: Arnd Bergmann <[email protected]>
> ---
> drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> index 451a4c9b3d30..04baa80494c6 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> @@ -429,7 +429,8 @@ static void csiphy_gen2_config_lanes(struct csiphy_device *csiphy,
> array_size = ARRAY_SIZE(lane_regs_sm8250[0]);
> break;
> default:
> - unreachable();
> + WARN(1, "unknown cspi version\n");
> + return;
> }
>
> for (l = 0; l < 5; l++) {
> --
> 2.35.1
>
Reviewed-by: Robert Foss <[email protected]>
On Fri, Dec 16, 2022, at 12:23, Peter Zijlstra wrote:
> On Thu, Dec 15, 2022 at 05:28:46PM +0100, Arnd Bergmann wrote:
>> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
>> index 451a4c9b3d30..04baa80494c6 100644
>> --- a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
>> +++ b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
>> @@ -429,7 +429,8 @@ static void csiphy_gen2_config_lanes(struct csiphy_device *csiphy,
>> array_size = ARRAY_SIZE(lane_regs_sm8250[0]);
>> break;
>> default:
>> - unreachable();
>> + WARN(1, "unknown cspi version\n");
>> + return;
>> }
>
> So no real objection here; but unreachable() does have an objtool
> annotation inside, so clearly the compiler managed to defeat that --
> perhaps we should look at that too.
Ah, I forgot this annotation existed. I see that this
particular objtool warning only happens with clang (I used
version 14.0.6), but it does not happen with gcc-12.2.
I see the function ends in
jmp .LBB3_45
.LBB3_54:
#APP
.Ltmp0:
.section .discard.unreachable,"",@progbits
.Ltmp1:
.long .Ltmp0-.Ltmp1
.text
#NO_APP
.Lfunc_end3:
.size csiphy_lanes_enable, .Lfunc_end3-csiphy_lanes_enable
# -- End function
full assembler output at https://pastebin.com/F8HGCUvk, object file
attached.
Arnd