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

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

[Kees Cook]

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;
         |             ^

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202401310423.XpCIk6KO-lkp@intel.com/
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 lib/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Makefile b/lib/Makefile
index 6b09731d8e61..bc36a5c167db 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -69,6 +69,7 @@ obj-$(CONFIG_HASH_KUNIT_TEST) += test_hash.o
 obj-$(CONFIG_TEST_IDA) += test_ida.o
 obj-$(CONFIG_TEST_UBSAN) += test_ubsan.o
 CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
+CFLAGS_test_ubsan.o += $(call cc-disable-warning, unused-but-set-variable)
 UBSAN_SANITIZE_test_ubsan.o := y
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
 obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
-- 
2.34.1

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

[Marco Elver]

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?

>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202401310423.XpCIk6KO-lkp@intel.com/
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  lib/Makefile | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/lib/Makefile b/lib/Makefile
> index 6b09731d8e61..bc36a5c167db 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -69,6 +69,7 @@ obj-$(CONFIG_HASH_KUNIT_TEST) += test_hash.o
>  obj-$(CONFIG_TEST_IDA) += test_ida.o
>  obj-$(CONFIG_TEST_UBSAN) += test_ubsan.o
>  CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
> +CFLAGS_test_ubsan.o += $(call cc-disable-warning, unused-but-set-variable)
>  UBSAN_SANITIZE_test_ubsan.o := y
>  obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
>  obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
> --
> 2.34.1
>

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

[Kees Cook]

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;
      |                          ^~~


-- 
Kees Cook

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

[Marco Elver]

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.