On Tue, 18 Aug 2020 at 09:25, Greg KH <gre...@linuxfoundation.org> wrote: > > On Tue, Aug 18, 2020 at 09:10:01AM +0200, Ard Biesheuvel wrote: > > On Tue, 18 Aug 2020 at 00:02, Nick Desaulniers <ndesaulni...@google.com> > > wrote: > > > > > > LLVM implemented a recent "libcall optimization" that lowers calls to > > > `sprintf(dest, "%s", str)` where the return value is used to > > > `stpcpy(dest, str) - dest`. This generally avoids the machinery involved > > > in parsing format strings. This optimization was introduced into > > > clang-12. Because the kernel does not provide an implementation of > > > stpcpy, we observe linkage failures for almost all targets when building > > > with ToT clang. > > > > > > The interface is unsafe as it does not perform any bounds checking. > > > Disable this "libcall optimization" via `-fno-builtin-stpcpy`. > > > > > > Unlike > > > commit 5f074f3e192f ("lib/string.c: implement a basic bcmp") > > > which cited failures with `-fno-builtin-*` flags being retained in LLVM > > > LTO, that bug seems to have been fixed by > > > https://reviews.llvm.org/D71193, so the above sha can now be reverted in > > > favor of `-fno-builtin-bcmp`. > > > > > > Cc: sta...@vger.kernel.org # 4.4 > > > > Why does a fix for Clang-12 have to be backported all the way to v4.4? > > How does that meet the requirements for stable patches? > > Because people like to build older kernels with new compliler versions. > > And those "people" include me, who doesn't want to keep around old > compilers just because my distro moved to the latest one... > > We've been doing this for the past 4+ years, for new versions of gcc, > keeping 4.4.y building properly with the bleeding edge of that compiler, > why is clang any different here? >
Fair enough. I am just struggling to match stable-kernel-rules.rst with the actual practices - perhaps it is time to update that document?