Re: [PATCH v2] lib/string.c: implement stpcpy

Arvind Sankar
2020-08-16T15:03:14Z

On Sun, Aug 16, 2020 at 07:22:35AM +0200, Sedat Dilek wrote:
> On Sun, Aug 16, 2020 at 2:19 AM 'Fangrui Song' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > Adding a definition without a declaration for stpcpy looks good.
> > Clang LTO will work.
> >
> > (If the kernel does not want to provide these routines,
> > is http://git.kernel.org/linus/6edfba1b33c701108717f4e036320fc39abe1912
> > probably wrong? (why remove -ffreestanding from the main Makefile) )
> >
>
> We had some many issues in arch/x86 where *FLAGS were removed or used
> differently and had to re-add them :-(.
>
> So if -ffreestanding is used in arch/x86 and was! used in top-level
> Makefile - it makes sense to re-add it back?
> ( I cannot speak for archs other than x86. )
>
> - Sedat -

-ffreestanding disables _all_ builtins and libcall optimizations, which
is probably not desirable. If we added it back, we'd need to also go
back to #define various string functions to the __builtin versions.

Though I don't understand the original issue, with -ffreestanding,
sprintf shouldn't have been turned into strcpy in the first place.

32-bit still has -ffreestanding -- I wonder if that's actually necessary
any more?

Why does -fno-builtin-stpcpy not work with clang LTO? Isn't that a
compiler bug?

Thanks.