arch/sim: replace macOS C++ constructor runtime hack with post-link patch

[xiaoxiang781216]

Summary

Replace the macOS sim C++ global constructor runtime hack (sim_macho_init.c)
with a post-link Mach-O section patching scheme so dyld no longer auto-runs
constructors before NuttX is initialized.

Impact

• Area: arch/sim (macOS host only). Linux behavior is unchanged.

Testing

• Build host: macOS (Ventura VM)
• Target: sim:nsh with CONFIG_HAVE_CXX=y / CONFIG_HAVE_CXXINITIALIZE=y
• Verified via standalone test (test_sinit7) that the C++ constructor is
  deferred past main() and is only invoked when explicitly called through
  the _sinit[]/_einit[] loop in lib_cxx_initialize().

Details

1. Link with -Wl,-ld_classic,-no_fixup_chains to keep the classic
   __mod_init_func pointer format (prevents ld64 from converting it to
   __init_offsets).
2. Post-link, run patch_macho_initsection.py (python3 + lief) to patch
   the Mach-O section type flags from MOD_INIT_FUNC_POINTERS /
   INIT_FUNC_OFFSETS to REGULAR, so dyld skips them.
3. Use the Mach-O auto-generated boundary symbols
   section$start$__DATA_CONST$__mod_init_func /
   section$end$__DATA_CONST$__mod_init_func, mapped via __asm() labels in
   arch/sim/include/arch.h to the common _sinit[]/_einit[] names used
   by lib_cxx_initialize().
4. Delete the old sim_macho_init.c runtime hack and the macOS-specific
   macho_call_saved_init_funcs() path in lib_cxx_initialize.c.

Dependency: pip install lief on the build host when
CONFIG_HAVE_CXXINITIALIZE=y.

[Copilot]

Pull request overview

This PR replaces the macOS simulator C++ constructor deferral mechanism with post-link Mach-O section patching, so dyld does not run constructors before NuttX initialization.

Changes:

• Removes the old runtime Mach-O constructor interception path.
• Adds macOS linker flags and post-build patching for Mach-O init sections.
• Maps macOS Mach-O section boundary symbols to _sinit / _einit.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
libs/libc/misc/lib_cxx_initialize.c	Uses the common _sinit / _einit constructor loop for macOS too.
arch/sim/src/sim/posix/sim_macho_init.c	Removes the previous runtime constructor-saving hack.
arch/sim/src/sim/CMakeLists.txt	Adds macOS link options and a post-build Mach-O patch command.
arch/sim/src/patch_macho_initsection.py	Adds the LIEF-based Mach-O section type patcher.
arch/sim/src/Makefile	Adds macOS linker flags and invokes the patcher in make builds.
arch/sim/include/arch.h	Adds macOS-specific _sinit / _einit asm symbol mappings.

---

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[toku-mac]

Hello. Regarding arch/sim/src/sim/CMakeLists.txt.

  add_custom_command(
    TARGET nuttx
    POST_BUILD
    COMMAND
      ${Python3_EXECUTABLE}
      ${CMAKE_CURRENT_SOURCE_DIR}/../patch_macho_initsection.py
      $<TARGET_FILE:nuttx>
    COMMENT "Patching Mach-O init section type flags")
endif()

add_custom_command(TARGET ...) can only be used in the directory where the target was created.
Since the nuttx executable is created in the top-level CMakeLists.txt, attaching a POST_BUILD command to it from here would not work.
Please use a custom target hooked into nuttx_post instead.

  add_custom_target(
    sim_patch_macho_initsection ALL
    COMMAND
      ${Python3_EXECUTABLE}
      ${CMAKE_CURRENT_SOURCE_DIR}/../patch_macho_initsection.py
      $<TARGET_FILE:nuttx>
    DEPENDS nuttx
    COMMENT "Patching Mach-O init section type flags")
  add_dependencies(nuttx_post sim_patch_macho_initsection)
endif()

[toku-mac]

about arch/sim/src/patch_macho_initsection.py.
On macOS 11 and later with Apple Silicon, binary re-signing is required.

Writing the file invalidates the ad-hoc signature that ld attached at link time, which causes the kernel to SIGKILL the process at exec.

import argparse
import subprocess
import sys

    if patched:
        fat.write(args.binary)

        if sys.platform == "darwin":
            subprocess.run(
                ["codesign", "--force", "--sign", "-", args.binary],
                check=True,
            )

    return 0

[xiaoxiang781216]

@toku-mac I have added you to my repo collaborator, please run the below command in your local nuttx git:

git remote add xiaoxiang781216 git@github.com:xiaoxiang781216/incubator-nuttx.git
git fetch xiaoxiang781216
git branch --track macos xiaoxiang781216/macos
git checkout macos
do the change you want
git commit --amend -s
git push -f xiaoxiang781216

since it's simpler to modify and update this patch by you directly.