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. Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/lkml/202210190108.ESC3pc3D-lkp@xxxxxxxxx/ Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> --- Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Makefile b/Makefile index f41ec8c8426b..bbf376931899 100644 --- a/Makefile +++ b/Makefile @@ -562,7 +562,7 @@ KBUILD_AFLAGS := -D__ASSEMBLY__ -fno-PIE 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) \ -- 2.38.1
