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@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/lkml/202210190108.ESC3pc3D-lkp@intel.com/
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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) \
projects / linux-stable / commitdiff