[PATCH v4 02/15] ARC: ABI Implementation

[Joseph Myers]

On Thu, 12 Mar 2020, Vineet Gupta via Libc-alpha wrote:

> diff --git a/sysdeps/arc/bits/endianness.h b/sysdeps/arc/bits/endianness.h
> new file mode 100644
> index 000000000000..8f17ca84b485
> --- /dev/null
> +++ b/sysdeps/arc/bits/endianness.h
> @@ -0,0 +1,15 @@
> +#ifndef _BITS_ENDIANNESS_H
> +#define _BITS_ENDIANNESS_H 1
> +
> +#ifndef _BITS_ENDIAN_H
> +# error "Never use <bits/endian.h> directly; include <endian.h> instead."
> +#endif
> +
> +/* ARC has selectable endianness.  */
> +#ifdef __BIG_ENDIAN__
> +# define __BYTE_ORDER __BIG_ENDIAN
> +#else
> +# define __BYTE_ORDER __LITTLE_ENDIAN
> +#endif

Elsewhere you say the port is little-endian only.  In such cases we 
generally have an error somewhere if you attempt to build glibc for the 
other endianness, to avoid an other-endian configuration accidentally 
building but not working and having a broken ABI.  For example, see what 
Nios II does: sysdeps/nios2/bits/endianness.h handles both endiannesses, 
but sysdeps/nios2/configure.ac produces an error for big-endian.

> +/* PLT jump into resolver passes PC of PLTn, while _dl_fixup expects the
> +   address of corresponding .rela.plt entry.  */
> +
> +#ifdef __A7__
> +# define ARC_PLT_SIZE	12
> +#else
> +# define ARC_PLT_SIZE	16
> +#endif

Is this some sort of ABI difference between two incompatible ABIs?  (The 
ABI document you pointed to only seems to mention 12-byte PLT entries.)

> +#define reloc_index						\
> +({								\
> +  unsigned long int plt0 = D_PTR (l, l_info[DT_PLTGOT]);	\
> +  unsigned long int pltn = reloc_arg;				\
> +  /* Exclude PL0 and PLT1.  */					\

Should PL0 be PLT0 here?

> +  unsigned long int idx = (pltn - plt0)/ARC_PLT_SIZE - 2;	\

Missing spaces around '/'.

> diff --git a/sysdeps/arc/gmp-mparam.h b/sysdeps/arc/gmp-mparam.h
> new file mode 100644
> index 000000000000..5580551483c8
> --- /dev/null
> +++ b/sysdeps/arc/gmp-mparam.h
> @@ -0,0 +1,23 @@
> +/* gmp-mparam.h -- Compiler/machine parameter header file.
> +
> +Copyright (C) 2017-2020 Free Software Foundation, Inc.
> +
> +This file is part of the GNU MP Library.
> +
> +The GNU MP 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 MP 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 MP Library; see the file COPYING.LIB.  If not, see
> +<https://www.gnu.org/licenses/>.  */
> +
> +#include <sysdeps/generic/gmp-mparam.h>
> +
> +#define IEEE_DOUBLE_BIG_ENDIAN 0

Plenty of architectures that have, or support, little-endian floating 
point do not have gmp-mparam.h at all.  IEEE_DOUBLE_BIG_ENDIAN is only 
used to define union ieee_double_extract, which is nowhere used in glibc.  
So I don't think you need this header at all (and it shows up the scope 
for a more general cleanup possible for other ports, I suspect only the 
x32 and mips64 versions of this header, the ones that define 
_LONG_LONG_LIMB for ILP32 configurations with 64-bit registers, are the 
only non-generic ones that do anything useful - but you don't need to do 
that cleanup).

-- 
Joseph S. Myers
joseph@codesourcery.com