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Implement a robust overflows_type() macro to test if a variable or constant value would overflow another variable or type. This can be used as a constant expression for static_assert() (which requires a constant expression[1][2]) when used on constant values. This must be constructed manually, since __builtin_add_overflow() does not produce a constant expression[3]. Additionally adds castable_to_type(), similar to __same_type(), but for checking if a constant value would overflow if cast to a given type. Add unit tests for overflows_type(), __same_type(), and castable_to_type() to the existing KUnit "overflow" test: [16:03:33] ================== overflow (21 subtests) ================== ... [16:03:33] [PASSED] overflows_type_test [16:03:33] [PASSED] same_type_test [16:03:33] [PASSED] castable_to_type_test [16:03:33] ==================== [PASSED] overflow ===================== [16:03:33] ============================================================ [16:03:33] Testing complete. Ran 21 tests: passed: 21 [16:03:33] Elapsed time: 24.022s total, 0.002s configuring, 22.598s building, 0.767s running [1] https://en.cppreference.com/w/c/language/_Static_assert [2] C11 standard (ISO/IEC 9899:2011): 6.7.10 Static assertions [3] https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html 6.56 Built-in Functions to Perform Arithmetic with Overflow Checking Built-in Function: bool __builtin_add_overflow (type1 a, type2 b, Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> Cc: Nathan Chancellor <nathan@kernel.org> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Tom Rix <trix@redhat.com> Cc: Daniel Latypov <dlatypov@google.com> Cc: Vitor Massaru Iha <vitor@massaru.org> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org> Cc: Jani Nikula <jani.nikula@intel.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: linux-hardening@vger.kernel.org Cc: llvm@lists.linux.dev Co-developed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20221024201125.1416422-1-gwan-gyeong.mun@intel.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.