#906 gcc7 implicit-fallthrough

[Niki W. Waibel]

hi team,

gcc7 warns about switch/case that may fallthrough (no break at the end of case). this can be easily fixed by a comment / fallthrough / or // fallthrough or attribute ((fallthrough)) at the position in which you'd place the break; otherwise.

i see warnings (maybe bugs!?) in
./os/hal/ports/STM32/LLD/TIMv1/hal_pwm_lld.c
and
./os/rt/src/chschd.c
in chschd.c there are comments already, but not exactly as above.

[Giovanni Di Sirio]

Thanks, fixed in all versions in repository.

[Niki W. Waibel]

hmm,

Compiling chschd.c
../chibios-svn/os/rt/src/chschd.c: In function 'wakeup':
../chibios-svn/os/rt/src/chschd.c:334:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
     chSemFastSignalI(tp->u.wtsemp);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../chibios-svn/os/rt/src/chschd.c:338:3: note: here
   case CH_STATE_WTCOND:
   ^~~~

still falls through with warning. it seems you have to put the comment right before the following case statement (even if there are some #if #else #endif)

$ svn diff ../chibios-svn/os/rt/src/chschd.c
Index: ../chibios-svn/os/rt/src/chschd.c
===================================================================
--- ../chibios-svn/os/rt/src/chschd.c   (revision 11070)
+++ ../chibios-svn/os/rt/src/chschd.c   (working copy)
@@ -332,9 +332,9 @@
 #if CH_CFG_USE_SEMAPHORES == TRUE
   case CH_STATE_WTSEM:
     chSemFastSignalI(tp->u.wtsemp);
-    /* Falls through.*/
 #endif
 #if (CH_CFG_USE_CONDVARS == TRUE) && (CH_CFG_USE_CONDVARS_TIMEOUT == TRUE)
+    /* Falls through.*/
   case CH_STATE_WTCOND:
     /* Falls through.*/
 #endif

then the warning is gone.

[Niki W. Waibel]

it seems,

$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (Fedora 7.1.0-5.fc27) 7.1.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

has removed the feature to get rid of the warning by using a comment.

i use __attribute__ ((fallthrough)); for now.

[Niki W. Waibel]

ups, i have to correct myself! i was playing with gcc -save-temps :-o (which might have removed the comments in some way, the attributes not).
--> the comments /* falls through */ or similar are NOT ignored. sorry for false report.