diff mbox series

[3/4] ubsan: Force -Wno-maybe-uninitialized only for GCC

Message ID 20201002221527.177500-4-keescook@chromium.org (mailing list archive)
State New, archived
Headers show
Series Clean up UBSAN Makefile | expand

Commit Message

Kees Cook Oct. 2, 2020, 10:15 p.m. UTC 
Clang handles 'maybe-uninitialized' better in the face of using UBSAN,
so do not make this universally disabled for UBSAN builds.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 lib/Kconfig.ubsan      | 6 ++++++
 scripts/Makefile.ubsan | 6 +++---
 2 files changed, 9 insertions(+), 3 deletions(-)

Comments

Nathan Chancellor Oct. 4, 2020, 7:16 a.m. UTC | #1 
On Fri, Oct 02, 2020 at 03:15:26PM -0700, Kees Cook wrote:
> Clang handles 'maybe-uninitialized' better in the face of using UBSAN,
> so do not make this universally disabled for UBSAN builds.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>

Well this patch is not strictly necessary because Clang does not support
-Wmaybe-uninitialized anyways :) its flags are -Wuninitialized and
-Wsometimes-uninitialized so the warning stays enabled for UBSAN as it
stands.

However, something like this could still worthwhile because it would
save us one call to cc-disable-warning (yay micro optimizations).

Maybe it just does not need to have a whole new symbol, just make it

ubsan-cflags-$(CONFIG_CC_IS_GCC)

instead of

ubsan-cflags-$(CONFIG_UBSAN)

No strong opinions either way though.

> ---
>  lib/Kconfig.ubsan      | 6 ++++++
>  scripts/Makefile.ubsan | 6 +++---
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index aeb2cdea0b94..1fc07f936e06 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -36,6 +36,12 @@ config UBSAN_KCOV_BROKEN
>  	  See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
>  	  in newer releases.
>  
> +config UBSAN_DISABLE_MAYBE_UNINITIALIZED
> +	def_bool CC_IS_GCC
> +	help
> +	  -fsanitize=* options makes GCC less smart than usual and
> +	  increases the number of 'maybe-uninitialized' false-positives.
> +
>  config CC_HAS_UBSAN_BOUNDS
>  	def_bool $(cc-option,-fsanitize=bounds)
>  
> diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
> index 72862da47baf..c5ef6bac09d4 100644
> --- a/scripts/Makefile.ubsan
> +++ b/scripts/Makefile.ubsan
> @@ -1,8 +1,8 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
> -# -fsanitize=* options makes GCC less smart than usual and
> -# increases the number of 'maybe-uninitialized' false-positives.
> -ubsan-cflags-$(CONFIG_UBSAN) += $(call cc-disable-warning, maybe-uninitialized)
> +# The "maybe-uninitialized" warning can be very noisy.
> +ubsan-cflags-$(CONFIG_UBSAN_DISABLE_MAYBE_UNINITIALIZED) += \
> +						$(call cc-disable-warning, maybe-uninitialized)
>  
>  # Enable available and selected UBSAN features.
>  ubsan-cflags-$(CONFIG_UBSAN_ALIGNMENT)		+= -fsanitize=alignment
> -- 
> 2.25.1
Kees Cook Oct. 6, 2020, 6:03 a.m. UTC | #2 
On Sun, Oct 04, 2020 at 12:16:14AM -0700, Nathan Chancellor wrote:
> On Fri, Oct 02, 2020 at 03:15:26PM -0700, Kees Cook wrote:
> > Clang handles 'maybe-uninitialized' better in the face of using UBSAN,
> > so do not make this universally disabled for UBSAN builds.
> > 
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> Well this patch is not strictly necessary because Clang does not support
> -Wmaybe-uninitialized anyways :) its flags are -Wuninitialized and
> -Wsometimes-uninitialized so the warning stays enabled for UBSAN as it
> stands.

Ah, yes. Heh. Well... perhaps I can just drop this patch.

> However, something like this could still worthwhile because it would
> save us one call to cc-disable-warning (yay micro optimizations).
> 
> Maybe it just does not need to have a whole new symbol, just make it
> 
> ubsan-cflags-$(CONFIG_CC_IS_GCC)
> 
> instead of
> 
> ubsan-cflags-$(CONFIG_UBSAN)

If it gets kept, I'd still like it gated on CONFIG_UBSAN in some way
(e.g. the patch has an implicit depends due to the "if UBSAN" section).

But yes, this patch is rather a no-op.
diff mbox series

Patch

diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index aeb2cdea0b94..1fc07f936e06 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -36,6 +36,12 @@  config UBSAN_KCOV_BROKEN
 	  See https://bugs.llvm.org/show_bug.cgi?id=45831 for the status
 	  in newer releases.
 
+config UBSAN_DISABLE_MAYBE_UNINITIALIZED
+	def_bool CC_IS_GCC
+	help
+	  -fsanitize=* options makes GCC less smart than usual and
+	  increases the number of 'maybe-uninitialized' false-positives.
+
 config CC_HAS_UBSAN_BOUNDS
 	def_bool $(cc-option,-fsanitize=bounds)
 
diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
index 72862da47baf..c5ef6bac09d4 100644
--- a/scripts/Makefile.ubsan
+++ b/scripts/Makefile.ubsan
@@ -1,8 +1,8 @@ 
 # SPDX-License-Identifier: GPL-2.0
 
-# -fsanitize=* options makes GCC less smart than usual and
-# increases the number of 'maybe-uninitialized' false-positives.
-ubsan-cflags-$(CONFIG_UBSAN) += $(call cc-disable-warning, maybe-uninitialized)
+# The "maybe-uninitialized" warning can be very noisy.
+ubsan-cflags-$(CONFIG_UBSAN_DISABLE_MAYBE_UNINITIALIZED) += \
+						$(call cc-disable-warning, maybe-uninitialized)
 
 # Enable available and selected UBSAN features.
 ubsan-cflags-$(CONFIG_UBSAN_ALIGNMENT)		+= -fsanitize=alignment