Bug 603398 – sys-devel/gcc: cortex-m multilibs support

• Product: Gentoo Linux
• Status: RESOLVED OBSOLETE

[Description hexum 2016-12-21 22:12:32 UTC]

Created attachment 457054 [details, diff]
arm-embedded-multilib.patch

Patch arm-embedded-multilib.patch for GCC adds cortex-m and cortex-r multilib support.

Got it here.
> Add support for ARM embedded multilibs
> https://gcc.gnu.org/ml/gcc-patches/2015-11/msg03400.html

This patch is made for gcc-6.2. Changes only applied when builded with appropriate with-multilib-list options.
Useful to make crossdev ebuilds suitable for building projects like opencm3.
> crossdev  -s0 --ex-gdb --genv 'EXTRA_ECONF="--with-multilib-list=armv6-m,armv7,armv7-m,armv7e-m,armv7-r,armv7-a,cortex-m7"' --target arm-none-eabi

Upstream did not accept this patch because of lack of related documentation changes.  But it works for me, I have got very latest arm-none-eabi toolchain.

Crossdev developers could be interested in.

[Comment 1 hexum 2017-08-31 21:36:35 UTC]

This was added to upstream

commit f3c3922fb10295a65cbb8cdfda7eced0eda125f8
Author: thopre01 <thopre01@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Tue Nov 22 14:01:57 2016 +0000

    Add multilib support for embedded bare-metal targets
    
    2016-11-22  Thomas Preud'homme  <[e-mail]>


git tag --contains f3c3922fb102
gcc-7_1_0-release
gcc-7_2_0-release


crossdev --g 7.2.0 -s1  --genv 'EXTRA_ECONF="--with-multilib-list=rmprofile"' --target arm-none-eabi

Got an error
/var/tmp/portage/cross-arm-none-eabi/gcc-7.2.0/work/build/gcc/include/stdint.h:9:16: fatal error: stdint.h: No such file or directory
 # include_next <stdint.h>

I'll investigate it later.

[Comment 2 hexum 2018-04-14 16:09:14 UTC]

rmprofile is available in the latest gcc releases and it works fine.
No patching is required anymore.

[Comment 3 Sam James 2023-09-28 11:52:30 UTC]

See also:

commit e61ffcd622d34570b294e7f4a3e922bdc980cd65
Author: Marek Behún <[e-mail]>
Date:   Thu Aug 18 20:01:58 2022 +0200

    toolchain.eclass: build multilibs for ARM's A, R and M architecture profiles

    For ARM targets, with USE=multilib and with CTARGET that does not imply
    any of --with-arch, --with-cpu, --with-mode or --with-float options to
    gcc's configuration (when arm_arch=arm), pass option
    --with-multilib-list=aprofile,rmprofile to gcc's configuration to make
    it build multilibs for A, R and M architecture profiles.

    This makes it possible to have one compiler capable of generating
    correct code (linking correct libgcc/CRT) for various ARM targets: from
    armv6 to armv7, for both soft float and half float, for various FPU
    types.

    Example of arm-none-eabi-gcc -print-libgcc-file-name output for various
    options:
      default:
        /usr/lib/gcc/arm-none-eabi/12.1.1/libgcc.a
      -mcpu=cortex-m0
        /usr/lib/gcc/arm-none-eabi/12.1.1/thumb/v6-m/nofp/libgcc.a
      -march=armv7-m
        /usr/lib/gcc/arm-none-eabi/12.1.1/thumb/v7-m/nofp/libgcc.a
      -march=armv7-a
        /usr/lib/gcc/arm-none-eabi/12.1.1/thumb/v7-a/nofp/libgcc.a
      -march=armv7-a -mhard-float -mfpu=neon
        /usr/lib/gcc/arm-none-eabi/12.1.1/thumb/v7-a+simd/hard/libgcc.a
      -march=armv7-a -mhard-float -mfpu=vfp
        /usr/lib/gcc/arm-none-eabi/12.1.1/thumb/v7-a+fp/hard/libgcc.a

    Signed-off-by: Marek Behún <[e-mail]>
    Signed-off-by: Sam James <[e-mail]>

which we later reverted:

commit 3e6f0d7e573c9141d2f3b5bb284caef999663294
Author: Marek Behún <[e-mail]>
Date:   Thu Aug 18 19:53:10 2022 +0200

    Revert "toolchain.eclass: ensure thumb mode for armv6m"

    This reverts commit 903b71810e0b270a7d494e16e2d799fcd95ae50f.

    The commit caused default libgcc to be built in thumb mode for armv6m
    target, but it broke subsequent compilation of newlib via crossdev.

    The whole reason of this commit was to have the compiler generate
    correct code when libgcc was used in thumb mode, but now this is not
    needed anymore, because now we configure gcc with
    --with-multilib-list=aprofile,rmprofile for CTARGET=arm-* when used with
    multilib, which generates compiler that builds correct binaries for
    -march=armv6-m even if libgcc is used.

    Signed-off-by: Marek Behún <[e-mail]>
    Closes: https://github.com/gentoo/gentoo/pull/26914
    Signed-off-by: Sam James <[e-mail]>

[Comment 4 Sam James 2023-09-28 11:53:45 UTC]

... and (we didn't revert this):

commit 903b71810e0b270a7d494e16e2d799fcd95ae50f
Author: Marek Behún <[e-mail]>
Date:   Mon May 30 13:00:09 2022 +0200

    toolchain.eclass: ensure thumb mode for armv6m

    Currently the eclass ensures thumb mode compilation for libgcc for
    armv7m targets
    with
      [[ ${arm_arch} == armv7? ]] && arm_arch=${arm_arch/7/7-}
      ...
      [[ ${arm_arch} == *-m ]] && confgcc+=( --with-mode=thumb )

    But libgcc should also be compiled in thumb mode for the armv6m target.

    Add the dash as is done for the armv7 case so that --with-mode=thumb
    option is added for armv6m.

    Signed-off-by: Marek Behún <[e-mail]>
    Closes: https://github.com/gentoo/gentoo/pull/25687
    Signed-off-by: Sam James <[e-mail]>