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As explained by Nick in the original issue: the kernel usually does a good job of providing library helpers that have similar semantics as their ordinary userspace libc equivalents, but -ffreestanding disables such libcall optimization and other related features in the compiler, which can lead to unexpected things such as CONFIG_FORTIFY_SOURCE not working (!). However, due to the desire for better control over unaligned accesses with respect to CONFIG_ARCH_STRICT_ALIGN, and also for avoiding the GCC bug https://gcc.gnu.org/PR109465, we do want to still disable optimizations for the memory libcalls (memcpy, memmove and memset for now). Use finer-grained -fno-builtin-* toggles to achieve this without losing source fortification and other libcall optimizations. Closes: https://github.com/ClangBuiltLinux/linux/issues/1897 Reported-by: Nathan Chancellor <nathan@kernel.org> Suggested-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: WANG Xuerui <git@xen0n.name> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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.