Messages in this thread | | | From | Nick Desaulniers <> | Date | Fri, 12 Jul 2019 09:48:08 -0700 | Subject | Re: [PATCH] waitqueue: fix clang -Wuninitialized warnings |
| |
On Fri, Jul 12, 2019 at 12:45 AM Arnd Bergmann <arnd@arndb.de> wrote: > > On Fri, Jul 12, 2019 at 2:49 AM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Wed, 3 Jul 2019 10:10:55 +0200 Arnd Bergmann <arnd@arndb.de> wrote: > > > <scratches head> > > > > Surely clang is being extraordinarily dumb here? > > > > DECLARE_WAIT_QUEUE_HEAD_ONSTACK() is effectively doing > > > > struct wait_queue_head name = ({ __init_waitqueue_head(&name) ; name; }) > > > > which is perfectly legitimate! clang has no business assuming that > > __init_waitqueue_head() will do any reads from the pointer which it was > > passed, nor can clang assume that __init_waitqueue_head() leaves any of > > *name uninitialized. > > > > Does it also warn if code does this? > > > > struct wait_queue_head name; > > __init_waitqueue_head(&name); > > name = name; > > > > which is equivalent, isn't it? > > No, it does not warn for this.
So I think this is just a bug in Clang, where it's getting tripped up due to the GNU C statement expression. See the example I put in this bug report: https://bugs.llvm.org/show_bug.cgi?id=42604
Clang is warning for this pattern of struct assignment, but not for non-aggregate (integral) assignment.
(I think that pattern is pretty cool; it makes it more straightforward to provide macro's that properly construct aggregates in C; in particular I feel like I've been looking for something like this to simply the use of __attribute__((__cleanup__)) to do RAII in C and make smart pointers, fd's, etc.).
Let's fix Clang, drop the kernel workaround, and thanks for the discussion. -- Thanks, ~Nick Desaulniers
| |