From: "Maciej W. Rozycki" <macro@mips.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: <libc-alpha@sourceware.org>, Alan Modra <amodra@gmail.com>
Subject: Re: [PATCH 2/2] libc-abis: Define ABSOLUTE ABI [BZ #19818][BZ #23307]
Date: Thu, 28 Jun 2018 13:49:00 -0000 [thread overview]
Message-ID: <alpine.DEB.2.00.1806280905490.20622@tp.orcam.me.uk> (raw)
In-Reply-To: <d1ee54d8-9491-28cb-3fcf-b13408d47b6a@redhat.com>
On Wed, 27 Jun 2018, Florian Weimer wrote:
> > > Is this really necessary? It essentially precludes backporting the
> > > fixes.
> > Thank you for your input. Of course bumping up the ABI version is not
> > itself required for the change to work, and all existing working binaries
> > will continue to.
> >
> > Technically it does not preclude backporting either, although of course
> > it is limited by the previous ABI bump, which is (in the reverse order by
> > version/date):
>
> Maybe I misunderstood what you were trying to do here.
>
> Will the EI_ABIVERSION in created binaries increase if the programmer simply
> upgrades binutils? Or will this happen only when particular features are
> used?
Only when this particular feature is required, like with the older ABI
versions defined so far. I've double-checked with binutils and the MIPS
target is the only one actively switching EI_ABIVERSION; all the remaining
targets appear to have the value fixed and I am not going to change that.
This is how the relevant part of the linker update in question looks
like:
Index: binutils/bfd/elfxx-mips.c
===================================================================
--- binutils.orig/bfd/elfxx-mips.c 2018-06-28 00:44:35.780943617 +0100
+++ binutils/bfd/elfxx-mips.c 2018-06-28 00:44:35.913406279 +0100
@@ -16305,13 +16449,14 @@ enum
MIPS_LIBC_ABI_MIPS_PLT,
MIPS_LIBC_ABI_UNIQUE,
MIPS_LIBC_ABI_MIPS_O32_FP64,
+ MIPS_LIBC_ABI_ABSOLUTE,
MIPS_LIBC_ABI_MAX
};
void
_bfd_mips_post_process_headers (bfd *abfd, struct bfd_link_info *link_info)
{
- struct mips_elf_link_hash_table *htab;
+ struct mips_elf_link_hash_table *htab = NULL;
Elf_Internal_Ehdr *i_ehdrp;
i_ehdrp = elf_elfheader (abfd);
@@ -16319,15 +16464,19 @@ _bfd_mips_post_process_headers (bfd *abf
{
htab = mips_elf_hash_table (link_info);
BFD_ASSERT (htab != NULL);
-
- if (htab->use_plts_and_copy_relocs && !htab->is_vxworks)
- i_ehdrp->e_ident[EI_ABIVERSION] = MIPS_LIBC_ABI_MIPS_PLT;
}
+ if (htab != NULL && htab->use_plts_and_copy_relocs && !htab->is_vxworks)
+ i_ehdrp->e_ident[EI_ABIVERSION] = MIPS_LIBC_ABI_MIPS_PLT;
+
if (mips_elf_tdata (abfd)->abiflags.fp_abi == Val_GNU_MIPS_ABI_FP_64
|| mips_elf_tdata (abfd)->abiflags.fp_abi == Val_GNU_MIPS_ABI_FP_64A)
i_ehdrp->e_ident[EI_ABIVERSION] = MIPS_LIBC_ABI_MIPS_O32_FP64;
+ /* Mark that we need support for absolute symbols in the dynamic loader. */
+ if (htab != NULL && htab->use_absolute_zero)
+ i_ehdrp->e_ident[EI_ABIVERSION] = MIPS_LIBC_ABI_ABSOLUTE;
+
_bfd_elf_post_process_headers (abfd, link_info);
}
and then `htab->use_absolute_zero' will be TRUE iff a GOT relocation has
been calculated to actually refer to a specially-created absolute symbol
used to address the issue covered by binutils PR ld/21375.
The flag will be FALSE if code has been relaxed to avoid referring the
GOT (by using immediate zero instead), in which case no absolute symbol
will have been specially created.
Does this explanation clear your concern?
Maciej
next prev parent reply other threads:[~2018-06-28 13:49 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-18 18:06 [PATCH 0/2] Accept absolute symbols whose value is zero [BZ #23307] Maciej W. Rozycki
2018-06-18 18:08 ` [PATCH 2/2] libc-abis: Define ABSOLUTE ABI [BZ #19818][BZ #23307] Maciej W. Rozycki
2018-06-25 20:33 ` Florian Weimer
2018-06-27 22:08 ` Maciej W. Rozycki
2018-06-28 6:59 ` Florian Weimer
2018-06-28 13:49 ` Maciej W. Rozycki [this message]
2018-06-28 13:54 ` Florian Weimer
2018-06-28 14:54 ` Maciej W. Rozycki
2018-06-29 16:29 ` Maciej W. Rozycki
2018-07-03 13:53 ` Carlos O'Donell
2018-07-05 15:42 ` [PATCH v2 " Maciej W. Rozycki
2018-07-05 16:29 ` Carlos O'Donell
2018-07-05 17:10 ` Maciej W. Rozycki
2018-07-05 18:02 ` Carlos O'Donell
2018-06-18 18:08 ` [PATCH 1/2] elf: Accept absolute (SHN_ABS) symbols whose value is zero [BZ #23307] Maciej W. Rozycki
2018-06-25 20:25 ` Florian Weimer
2018-06-29 16:13 ` [committed v2 " Maciej W. Rozycki
2018-06-29 17:41 ` Joseph Myers
2018-06-29 18:05 ` Maciej W. Rozycki
2018-06-25 19:14 ` [PING][PATCH 0/2] Accept absolute " Maciej W. Rozycki
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