Hi Josh,


Le ven., févr. 14, 2020 at 10:37, Josh Poimboeuf [off-list ref] 
a écrit :

In the second loop of ingenic_pinconf_set(), it annotates the switch
default case as unreachable().  The annotation is technically correct,
because that same case would have resulted in an early return in the
previous loop.

However, if a bug were to get introduced later, for example if an
additional case were added to the first loop without adjusting the
second loop, it would result in nasty undefined behavior: most likely
the function's generated code would fall through to the next function.

Another issue is that, while objtool normally understands 
unreachable()
annotations, there's one special case where it doesn't: when the
annotation occurs immediately after a 'ret' instruction.  That happens
to be the case here because unreachable() is immediately before the
return.

So change the unreachable() to BUG() so that the unreachable code, if
ever executed, would panic instead of introducing undefined behavior.
This also makes objtool happy.

I don't like the idea that you change this driver's code just to work 
around a bug in objtool, and I don't like the idea of working around a 
future bug that shouldn't be introduced in the first place.

-Paul