On Thu, Oct 30, 2025 at 2:42 AM Alexandre Oliva <[email protected]> wrote:
>
> On Oct 27, 2025, Richard Biener <[email protected]> wrote:
>
> > So on x86-64-linux this is a cross configuration?
>
> It's one of those cross-natives corner cases.
>
> > Or is this able to bootstrap itself but then resulting in a 32bit host
> > compiler?
>
> Yeah, it can bootstrap. (It needs an additional tweak to fix multilibs
> in libgnat.)
If bootstrap is used, it is the same as i686-linux with
--with-multilib-list=m32,m64.
> But the interesting use case for this is the non-bootstrap case.
If it is the case, why not use x86-64-linux --with-abi=m32?
> A variant of this change that enables multilibs, and that could be more
> interesting to bootstrap, can also bootstrap starting with an
> x86_64-linux-gnu compiler with -m64 added to BOOT_CFLAGS, along with an
> -L flag to find the 64-bit libstdc++, but you hit post-bootstrap
> incompatibilities building e.g. fixincludes (and gnattools?) between the
> 64-bit libiberty (and other bootstrapped libraries), and the 32-bit
> outputs from the bootstrapped compiler used to build the post-bootstrap
> host tools.
>
> Non-bootstrapped builds don't hit this incompatibility, because the
> initial 64-bit compiler, rather than the just-built one, is used to
> build these host tools.
>
> Here's an incremental change, also by Olivier Hainque, that enables
> biarch -m32-defaulting x86_64-linux-gnum32.
>
>
> [PATCH] Turn x86_64-m32 configurations into biarch defaulting to m32
>
> diff --git a/gcc/config.gcc b/gcc/config.gcc
> index 8d96ef00005ad..7c85d04184b88 100644
> --- a/gcc/config.gcc
> +++ b/gcc/config.gcc
> @@ -689,8 +689,7 @@ x86_64-*-*)
> exit 1
> esac
> case ${with_multilib_list} in
> - default | m32)
> - with_multilib_list=m32
> + default | *m32*)
> ;;
> *)
> echo "Invalid multilib list for m32 target"
> @@ -714,6 +713,7 @@ x86_64-*-*)
> tm_file="i386/biarchx32.h ${tm_file}"
> ;;
> 32 | m32)
> + tm_file="i386/biarch32.h ${tm_file}"
> ;;
> *)
> echo "Unknown ABI used in --with-abi=$with_abi"
> diff --git a/gcc/config/i386/biarch32.h b/gcc/config/i386/biarch32.h
> new file mode 100644
> index 0000000000000..116cd68acc838
> --- /dev/null
> +++ b/gcc/config/i386/biarch32.h
> @@ -0,0 +1,29 @@
> +/* Make configure files to produce biarch compiler defaulting to 64bit mode.
> + This file must be included very first, while the OS specific file later
> + to overwrite otherwise wrong defaults.
> + Copyright (C) 2001-2025 Free Software Foundation, Inc.
> + Contributed by Bo Thorsen <[email protected]>.
> +
> +This file is part of GCC.
> +
> +GCC is free software; you can redistribute it and/or modify
> +it under the terms of the GNU General Public License as published by
> +the Free Software Foundation; either version 3, or (at your option)
> +any later version.
> +
> +GCC 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 General Public License for more details.
> +
> +Under Section 7 of GPL version 3, you are granted additional
> +permissions described in the GCC Runtime Library Exception, version
> +3.1, as published by the Free Software Foundation.
> +
> +You should have received a copy of the GNU General Public License and
> +a copy of the GCC Runtime Library Exception along with this program;
> +see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> +<http://www.gnu.org/licenses/>. */
> +
> +#define TARGET_64BIT_DEFAULT 0
> +#define TARGET_BI_ARCH 3
> diff --git a/gcc/config/i386/i386-options.cc b/gcc/config/i386/i386-options.cc
> index dadcf7664c632..443041789555b 100644
> --- a/gcc/config/i386/i386-options.cc
> +++ b/gcc/config/i386/i386-options.cc
> @@ -2018,22 +2018,35 @@ ix86_option_override_internal (bool main_args_p,
> #ifdef TARGET_BI_ARCH
> else
> {
> -#if TARGET_BI_ARCH == 1
> - /* When TARGET_BI_ARCH == 1, by default, OPTION_MASK_ABI_64
> - is on and OPTION_MASK_ABI_X32 is off. We turn off
> - OPTION_MASK_ABI_64 if OPTION_MASK_ABI_X32 is turned on by
> - -mx32. */
> - if (TARGET_X32_P (opts->x_ix86_isa_flags))
> - opts->x_ix86_isa_flags &= ~OPTION_MASK_ABI_64;
> -#else
> - /* When TARGET_BI_ARCH == 2, by default, OPTION_MASK_ABI_X32 is
> - on and OPTION_MASK_ABI_64 is off. We turn off
> - OPTION_MASK_ABI_X32 if OPTION_MASK_ABI_64 is turned on by
> - -m64 or OPTION_MASK_CODE16 is turned on by -m16. */
> - if (TARGET_LP64_P (opts->x_ix86_isa_flags)
> - || TARGET_16BIT_P (opts->x_ix86_isa_flags))
> - opts->x_ix86_isa_flags &= ~OPTION_MASK_ABI_X32;
> -#endif
> + switch (TARGET_BI_ARCH)
> + {
> + case 1:
> + /* When TARGET_BI_ARCH == 1, by default, OPTION_MASK_ABI_64
> + is on and OPTION_MASK_ABI_X32 is off. We turn off
> + OPTION_MASK_ABI_64 if OPTION_MASK_ABI_X32 is turned on by
> + -mx32. */
> + if (TARGET_X32_P (opts->x_ix86_isa_flags))
> + opts->x_ix86_isa_flags &= ~OPTION_MASK_ABI_64;
> + break;
> +
> + case 2:
> + /* When TARGET_BI_ARCH == 2, by default, OPTION_MASK_ABI_X32 is
> + on and OPTION_MASK_ABI_64 is off. We turn off
> + OPTION_MASK_ABI_X32 if OPTION_MASK_ABI_64 is turned on by
> + -m64 or OPTION_MASK_CODE16 is turned on by -m16. */
> + if (TARGET_LP64_P (opts->x_ix86_isa_flags)
> + || TARGET_16BIT_P (opts->x_ix86_isa_flags))
> + opts->x_ix86_isa_flags &= ~OPTION_MASK_ABI_X32;
> +
> + case 3:
> + /* When TARGET_BI_ARCH == 3, by default, OPTION_MASK_ABI_X32 and
> + OPTION_MASK_ABI_64 are both off. */
> + break;
> +
> + default:
> + gcc_unreachable();
> + }
> +
> if (TARGET_64BIT_P (opts->x_ix86_isa_flags)
> && TARGET_IAMCU_P (opts->x_target_flags))
> sorry ("Intel MCU psABI isn%'t supported in %s mode",
>
>
> --
> Alexandre Oliva, happy hacker https://blog.lx.oliva.nom.br/
> Free Software Activist FSFLA co-founder GNU Toolchain Engineer
> More tolerance and less prejudice are key for inclusion and diversity.
> Excluding neuro-others for not behaving ""normal"" is *not* inclusive!
--
H.J.
