| From: "Jason A. Donenfeld" <Jason@zx2c4.com> |
| Subject: kbuild: treat char as always unsigned |
| Date: Wed, 19 Oct 2022 14:30:34 -0600 |
| |
| Recently, some compile-time checking I added to the clamp_t family of |
| functions triggered a build error when a poorly written driver was |
| compiled on ARM, because the driver assumed that the naked `char` type is |
| signed, but ARM treats it as unsigned, and the C standard says it's |
| architecture-dependent. |
| |
| I doubt this particular driver is the only instance in which unsuspecting |
| authors make assumptions about `char` with no `signed` or `unsigned` |
| specifier. We were lucky enough this time that that driver used |
| `clamp_t(char, negative_value, positive_value)`, so the new checking code |
| found it, and I've sent a patch to fix it, but there are likely other |
| places lurking that won't be so easily unearthed. |
| |
| So let's just eliminate this particular variety of heisensign bugs |
| entirely. Set `-funsigned-char` globally, so that gcc makes the type |
| unsigned on all architectures. |
| |
| This will break things in some places and fix things in others, so this |
| will likely cause a bit of churn while reconciling the type misuse. |
| |
| Link: https://lkml.kernel.org/r/20221019203034.3795710-1-Jason@zx2c4.com |
| Link: https://lore.kernel.org/lkml/202210190108.ESC3pc3D-lkp@intel.com/ |
| Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> |
| Cc: Masahiro Yamada <masahiroy@kernel.org> |
| Cc: Kees Cook <keescook@chromium.org> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> |
| Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| Makefile | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/Makefile~kbuild-treat-char-as-always-unsigned |
| +++ a/Makefile |
| @@ -562,7 +562,7 @@ KBUILD_AFLAGS := -D__ASSEMBLY__ -fno-P |
| KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \ |
| -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \ |
| -Werror=implicit-function-declaration -Werror=implicit-int \ |
| - -Werror=return-type -Wno-format-security \ |
| + -Werror=return-type -Wno-format-security -funsigned-char \ |
| -std=gnu11 |
| KBUILD_CPPFLAGS := -D__KERNEL__ |
| KBUILD_RUSTFLAGS := $(rust_common_flags) \ |
| _ |
