Re: V2 [PATCH] gas: Generate a new section for SHF_GNU_RETAIN

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

On Fri, Dec 4, 2020 at 8:43 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Fri, Dec 4, 2020 at 7:29 AM Jozef Lawrynowicz
> <jozef.l@mittosystems.com> wrote:
> >
> > On Fri, Dec 04, 2020 at 05:52:54AM -0800, H.J. Lu wrote:
> > > For
> > >       .globl  foo2
> > >       .section        .data.foo,"aR"
> > >       .align 4
> > >       .type   foo2, @object
> > >       .size   foo2, 4
> > > foo2:
> > >       .long   2
> > >       .globl  foo1
> > >       .section        .data.foo
> > >       .align 4
> > >       .type   foo1, @object
> > >       .size   foo1, 4
> > > foo1:
> > >       .long   1
> > >
> > > generate a new section if the SHF_GNU_RETAIN bit doesn't match.
> > >
> > >       * config/obj-elf.c (SEC_ASSEMBLER_SHF_MASK): New.
> > >       (get_section_by_match): Also check if SEC_ASSEMBLER_SHF_MASK of
> > >       sh_flags matches.  Rename info to sh_info.
> > >       (obj_elf_change_section): Rename info to sh_info.
> > >       (obj_elf_section): Rename info to sh_info.  Set sh_flags for
> > >       SHF_GNU_RETAIN.
> > >       * config/obj-elf.h (elf_section_match): Rename info to sh_info.
> > >       Add sh_flags.
> > >       * testsuite/gas/elf/elf.exp: Run section27.
> > >       * testsuite/gas/elf/section24b.d: Updated.
> > >       * testsuite/gas/elf/section27.d: New file.
> > >       * testsuite/gas/elf/section27.s: Likewise.
> > > ---
> > >  gas/config/obj-elf.c               | 21 ++++++++++++------
> > >  gas/config/obj-elf.h               |  3 ++-
> > >  gas/testsuite/gas/elf/elf.exp      |  1 +
> > >  gas/testsuite/gas/elf/section24b.d | 10 ++++++---
> > >  gas/testsuite/gas/elf/section27.d  | 14 ++++++++++++
> > >  gas/testsuite/gas/elf/section27.s  | 34 ++++++++++++++++++++++++++++++
> > >  6 files changed, 73 insertions(+), 10 deletions(-)
> > >  create mode 100644 gas/testsuite/gas/elf/section27.d
> > >  create mode 100644 gas/testsuite/gas/elf/section27.s
> >
> > I just want to check that we are OK with the fact that a .section
> > directive without any flags will always use the default flags, even if
> > the section previously had the 'R' flag set. I suppose this is just
> > standard behavior and how the .section directive has always behaved.
>
> Correct.
>
> > $ cat asm-tester.s
> > .section .data.foo,"awR"
> > .word 0
> > .section .data.foo
> > .word 0
> > $ as asm-tester.s -o tester.o
> > $ readelf --wide -S tester.o
> > ...
> >   [ 4] .data.foo         PROGBITS        0000000000000000 000040 000002 00 WAR  0   0  1
> >   [ 5] .data.foo         PROGBITS        0000000000000000 000042 000002 00  WA  0   0  1
> > ...
> >
> > Also, I think the following change should be added, since the OR'ing of
> > SHF_GNU_RETAIN flag between sections, from the original patch, is now
> > redundant.
> >
> > diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
> > index 54d42d9ecb..9ac53e4d0e 100644
> > --- a/gas/config/obj-elf.c
> > +++ b/gas/config/obj-elf.c
> > @@ -806,17 +806,9 @@ obj_elf_change_section (const char *name,
> >                 as_bad (_("changed section attributes for %s"), name);
> >             }
> >           else
> > -           {
> > -             /* Don't overwrite a previously set SHF_GNU_RETAIN flag for the
> > -                section.  The entire section must be marked retained.  */
> > -             if ((elf_tdata (stdoutput)->has_gnu_osabi & elf_gnu_osabi_retain)
> > -                 && ((elf_section_flags (old_sec) & SHF_GNU_RETAIN)))
> > -               attr |= SHF_GNU_RETAIN;
> > -
> > -             /* FIXME: Maybe we should consider removing a previously set
> > -                processor or application specific attribute as suspicious ?  */
> > -             elf_section_flags (sec) = attr;
> > -           }
> > +           /* FIXME: Maybe we should consider removing a previously set
> > +              processor or application specific attribute as suspicious ?  */
> > +           elf_section_flags (sec) = attr;
> >
> >           if ((flags & SEC_MERGE) && old_sec->entsize != (unsigned) entsize)
> >             as_bad (_("changed section entity size for %s"), name);
> >
>
> Fixed.
>
> Here is the updated patch.  OK for master?
>
> Thanks.
>

Hi Alan, Nick,

Can you take a look at this

https://sourceware.org/pipermail/binutils/2020-December/114407.html

Thanks.

-- 
H.J.