Clang has never correctly compiled the FORTIFY_SOURCE defenses due to
a couple bugs:
Eliding inlines with matching __builtin_* names
https://bugs.llvm.org/show_bug.cgi?id=50322
Incorrect __builtin_constant_p() of some globals
https://bugs.llvm.org/show_bug.cgi?id=41459
In the process of making improvements to the FORTIFY_SOURCE defenses, the
first (silent) bug (coincidentally) becomes worked around, but exposes
the latter which breaks the build. As such, Clang must not be used with
CONFIG_FORTIFY_SOURCE until at least latter bug is fixed (in Clang 13),
and the fortify routines have been rearranged.
Update the Kconfig to reflect the reality of the current situation.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/lkml/CAKwvOd=A+ueGV2ihdy5GtgR2fQbcXjjAtVxv3=cPjffpebZB7A@mail.gmail.com
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