Re: [PATCH 6/6] x86: Fix -Os build (BZ #29576)

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, Oct 5, 2022 at 10:38 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 05/10/22 14:21, H.J. Lu wrote:
> > On Wed, Oct 5, 2022 at 7:10 AM Carlos O'Donell <carlos@redhat.com> wrote:
> >>
> >> On Wed, Sep 21, 2022 at 10:51:08AM -0300, Adhemerval Zanella via Libc-alpha wrote:
> >>> The compiler might transform __stpcpy calls (which are routed to
> >>> __builtin_stpcpy as an optimization) to strcpy and x86_64 strcpy
> >>> multiarch implementation does not build any working symbol due
> >>> ISA_SHOULD_BUILD not being evaluated for IS_IN(rtld).
> >>
> >> Ohhhhhh... that is interesting. This changes the strcpy used in rtld for
> >> all x86_64 build options, and I'm going to ACK this, but we may need to
> >> revisit this if it shows up in a profile.
> >
> > Will this lead to both strcpy and stpcpy in ld.so? Currently there is only
> > stpcpy in ld.so.
>
> I think that is expected behavior if compiler creates a reference for a
> supported string function in the loader (rtld build pulls the
> implementation).

strcpy is only generated in dl-profile.os:

   text    data     bss     dec     hex filename
   2716       0      72    2788     ae4 dl-profile.os (-O2)
   2265       0      72    2337     921 dl-profile.os (-Os)
   1840       0       0    1840     730  strcpy.os

Should we compile dl-profile.c with -O2 with

CFLAGS-dl-profile.c += $(if $(findstring -Os,$(+cflags)), -O2)

It will create a smaller ld.so.

> >
> >> CC'ing HJ here in case he wants to comment as a machine maintainer.
> >>
> >> LGTM.
> >>
> >> No regressions on x86_64.
> >>
> >> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
> >> Tested-by: Carlos O'Donell <carlos@redhat.com>
> >>
> >>> Checked on x86_64-linux-gnu.
> >>> ---
> >>>  sysdeps/x86_64/multiarch/rtld-strcpy.S | 18 ++++++++++++++++++
> >>>  1 file changed, 18 insertions(+)
> >>>  create mode 100644 sysdeps/x86_64/multiarch/rtld-strcpy.S
> >>>
> >>> diff --git a/sysdeps/x86_64/multiarch/rtld-strcpy.S b/sysdeps/x86_64/multiarch/rtld-strcpy.S
> >>> new file mode 100644
> >>> index 0000000000..19439c553d
> >>> --- /dev/null
> >>> +++ b/sysdeps/x86_64/multiarch/rtld-strcpy.S
> >>> @@ -0,0 +1,18 @@
> >>> +/* Copyright (C) 2022 Free Software Foundation, Inc.
> >>> +   This file is part of the GNU C Library.
> >>> +
> >>> +   The GNU C Library is free software; you can redistribute it and/or
> >>> +   modify it under the terms of the GNU Lesser General Public
> >>> +   License as published by the Free Software Foundation; either
> >>> +   version 2.1 of the License, or (at your option) any later version.
> >>> +
> >>> +   The GNU C Library is distributed in the hope that it will be useful,
> >>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> >>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> >>> +   Lesser General Public License for more details.
> >>> +
> >>> +   You should have received a copy of the GNU Lesser General Public
> >>> +   License along with the GNU C Library; if not, see
> >>> +   <https://www.gnu.org/licenses/>.  */
> >>> +
> >>> +#include "../strcpy.S"
> >>
> >> OK. Uses Makeconfig:sysd-rules-patterns to capture rtld-*.
> >>
> >>> --
> >>> 2.34.1
> >>>
> >>
> >
> >



-- 
H.J.