Re: [PATCH] ubsan: Silence W=1 warnings in self-test

[Marco Elver <elver@google.com>]

On Fri, 2 Feb 2024 at 11:41, Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Feb 02, 2024 at 10:57:11AM +0100, Marco Elver wrote:
> > On Fri, 2 Feb 2024 at 10:46, Kees Cook <keescook@chromium.org> wrote:
> > >
> > > Silence a handful of W=1 warnings in the UBSan selftest, which set
> > > variables without using them. For example:
> > >
> > >    lib/test_ubsan.c:101:6: warning: variable 'val1' set but not used [-Wunused-but-set-variable]
> > >      101 |         int val1 = 10;
> > >          |             ^
> >
> > This is the shift_out_of_bounds test? It looks like the neg and wrap
> > variables are volatile but the written-to variables aren't.
> > Technically the compiler just has to emit the reads to neg and wrap,
> > and can entirely omit the writes to val1 and val2.
> >
> > Does making it volatile fix the warning?
>
> It does for some, but not all:
>
> ../lib/test_ubsan.c: In function 'test_ubsan_out_of_bounds':
> ../lib/test_ubsan.c:115:22: warning: variable 'arr' set but not used [-Wunused-but-set-variable]
>   115 |         volatile int arr[4];
>       |                      ^~~
> ../lib/test_ubsan.c:114:23: warning: variable 'above' set but not used [-Wunused-but-set-variable]
>   114 |         volatile char above[4] = { }; /* Protect surrounding memory. */
>       |                       ^~~~~
> ../lib/test_ubsan.c: In function 'test_ubsan_load_invalid_value':
> ../lib/test_ubsan.c:137:44: warning: variable 'eptr' set but not used [-Wunused-but-set-variable]
>   137 |         enum ubsan_test_enum eval, eval2, *eptr;
>       |                                            ^~~~
> ../lib/test_ubsan.c:136:26: warning: variable 'ptr' set but not used [-Wunused-but-set-variable]
>   136 |         bool val, val2, *ptr;
>       |                          ^~~

Then I'd just combine the compiler flag with switching most of these
variables to volatile so the tests keep working if the compiler
decides to optimize too much.