Build failing on newer GCCs due to new implicit fallthrough detection

[vancluever]

--- kern_rndpool.pico ---
src/buildrump.sh/src/lib/librump/../../sys/rump/../kern/kern_rndpool.c: In function 'rndpool_add_data':
src/buildrump.sh/src/lib/librump/../../sys/rump/../kern/kern_rndpool.c:184:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
    val = *buf++;
    ~~~~^~~~~~~~
src/buildrump.sh/src/lib/librump/../../sys/rump/../kern/kern_rndpool.c:185:3: note: here
   case 2:
   ^~~~
src/buildrump.sh/src/lib/librump/../../sys/rump/../kern/kern_rndpool.c:186:8: error: this statement may fall through [-Werror=implicit-fallthrough=]
    val = val << 8 | *buf++;
    ~~~~^~~~~~~~~~~~~~~~~~~
src/buildrump.sh/src/lib/librump/../../sys/rump/../kern/kern_rndpool.c:187:3: note: here
   case 1:
   ^~~~
cc1: all warnings being treated as errors
*** [kern_rndpool.pico] Error code 1

This is my first time giving the project a spin, and also I'd imagine this specific problem is new-ish given that fallthrough detection was recently added to GCC. Adding -F CFLAGS=-Wimplicit-fallthrough=0 fixed it for me and got the build going again, but I thought I'd send this in so that it could be looked at and addressed in whatever way the project wants to address it (I'd imagine either by adding something specific to GCC or by adding the appropriate fallthrough metadata to the affected source files).

[vancluever]

Update: Going further into the tutorial, looks like the problem also presents itself in rumpctrl too. To fix that I had to add support to pass through flags and add -F CWARNFLAGS=-Wno-error=format-truncation -F CWARNFLAGS=-Werror=implicit-fallthrough=0.

[yarwelp]

@vancluever

To fix that I had to add support to pass through flags

Can you make a pull request on https://github.com/rumpkernel/rumpctrl for the changes you made for the rumpctrl build script to support pass through flags?

[K0zka]

failing on ubuntu 18.04 gcc version 7.3.0

[zatkh]

The same, fails on aarch64 Ubuntu 18.04 gcc 7.3.0. Adding the flags seems a short term solution, then all tests fails.