Re: [PATCH 1/4] Makefile: add -fno-builtin-stpcpy

[Nick Desaulniers]

On Mon, Aug 17, 2020 at 3:31 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>
> On 2020-08-17 15:02, Nick Desaulniers 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`.
> >
>
> stpcpy() and (to a lesser degree) mempcpy() are fairly useful routines
> in general. Perhaps we *should* provide them?

Sorry, I forgot to provide context of the previous thread, which is
worth a read.  To answer this question specifically (or at least for
stpcpy), the answer from the previous thread was (via Kees): "No;
please no more unbounded string.h routines":
https://lore.kernel.org/lkml/202008150921.B70721A359@keescook/
-- 
Thanks,
~Nick Desaulniers