Re: [PATCH v3 3/9] s390/string: Add -ffreestanding compile option to string.o

[Heiko Carstens <hca@linux.ibm.com>]

On Tue, Jun 09, 2026 at 02:23:23PM +0200, Juergen Christ wrote:
> > Use -ffreestanding for string.o to avoid that the compiler generates
> > calls into themselves for standard library functions like memset().
> > 
> > Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> > ---
> >  arch/s390/boot/Makefile | 5 +++++
> >  arch/s390/lib/Makefile  | 5 +++++
> >  2 files changed, 10 insertions(+)
> > 
> > diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
> > index a1e719a79d38..e1f82d118bc9 100644
> > --- a/arch/s390/boot/Makefile
> > +++ b/arch/s390/boot/Makefile
> > @@ -25,6 +25,11 @@ KBUILD_CFLAGS += $(call cc-option, -Wno-default-const-init-unsafe)
> >  
> >  CFLAGS_sclp_early_core.o += -I$(srctree)/drivers/s390/char
> >  
> > +# string.o implements standard library functions like memset/memcpy etc.
> > +# Use -ffreestanding to ensure that the compiler does not try to "optimize"
> > +# them into calls to themselves.
> > +CFLAGS_string.o = -ffreestanding
> > +
> 
> Other places use simply expanded variables instead of recursively
> expanded variables for CFLAGS or LDFLAGS.  Is this an issue here?

I just copied the above from the generic lib/Makefile, since I didn't
want to make our logic more special.

> Otherwise, -ffreestanding turns on -fno-builtin which then turns off
> -ftree-loop-distribute-patterns which would detect the
> memset/memcpy/memmove loops in GCC.  So that is one way to make sure
> this does not happen.
> 
> Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>

Thanks!