Loading dylib in python fails on macOS Big Sur: `Symbol not found: ___addtf3`

Question

I have trouble when loading a custom mylib.dylib in python3.7 on Mac OS X Big Sur 11.1:

OSError                                   Traceback (most recent call last)
<ipython-input-7-21ad9f6d803b> in <module>
     12 try:
---> 13     mylib = ctypes.CDLL(mylib_path)
     14 except OSError:

~/opt/anaconda3/lib/python3.7/ctypes/__init__.py in __init__(self, name, mode, handle, use_errno, use_last_error)
    363         if handle is None:
--> 364             self._handle = _dlopen(self._name, mode)
    365         else:

OSError: dlopen(mylib.dylib, 6): Symbol not found: ___addtf3
  Referenced from: /usr/local/opt/gcc/lib/gcc/10/libquadmath.0.dylib
  Expected in: flat namespace
 in /usr/local/opt/gcc/lib/gcc/10/libquadmath.0.dylib

However exactly the same mylib.dylib is loading successfully with exactly this python code on Mac OS X 10.15 Catalina. Moreover, exactly the same mylib binary runs successfully on my Big Sur 11.1 when compiled as an executable, not as a shared library.

Detailed step-by-step description:

1. I build a C++ code in a shared library using bazel on Mac OS X Big Sur 11.1:

bazel build :mylib.dylib

BUILD file is:

cc_binary(
    name = "mylib.dylib",
    srcs = ["mylib.cc", "mylib.h", "mylib_external.cc", "mylib_external.h"],
    deps = [
        ...some dependencies...
    ],
    linkshared = 1,
)

.bazelrc file is:

# Basic build settings
build --jobs 128
build --define='absl=1'
build --enable_platform_specific_config

# macOS
build:macos --cxxopt=-std=c++17
build:macos --host_cxxopt=-std=c++17
build:macos --copt=-w

# Sets the default Apple platform to macOS.
build --apple_platform_type=macos

# Allow debugging with XCODE
build --apple_generate_dsym

build:darwin_x86_64 --apple_platform_type=macos
build:darwin_x86_64 --macos_minimum_os=10.12
build:darwin_x86_64 --cpu=darwin_x86_64

2. Then I try to load it in python3.7:

import sys, platform
import ctypes, ctypes.util

mylib_path = ctypes.util.find_library("mylib")
if not mylib_path:
    print("Unable to find the specified library.")
    sys.exit()

try:
    mylib = ctypes.CDLL(mylib_path)
except OSError:
    print("Unable to load the specified library.")
    sys.exit()

And it gives me:

OSError                                   Traceback (most recent call last)
<ipython-input-7-21ad9f6d803b> in <module>
     12 try:
---> 13     mylib = ctypes.CDLL(mylib_path)
     14 except OSError:

~/opt/anaconda3/lib/python3.7/ctypes/__init__.py in __init__(self, name, mode, handle, use_errno, use_last_error)
    363         if handle is None:
--> 364             self._handle = _dlopen(self._name, mode)
    365         else:

OSError: dlopen(mylib.dylib, 6): Symbol not found: ___addtf3
  Referenced from: /usr/local/opt/gcc/lib/gcc/10/libquadmath.0.dylib
  Expected in: flat namespace
 in /usr/local/opt/gcc/lib/gcc/10/libquadmath.0.dylib

A possible solution to the same problem was discussed in this GitHub issue, but for me, changing DYLD_LIBRARY_PATH does not work.

3. I tried to set the path to libgcc_ext.10.4.dylib in libquadmath.0.dylib:

install_name_tool -change /usr/lib/libSystem.B.dylib /usr/local/opt/gcc/lib/gcc/10/libgcc_ext.10.4.dylib /usr/local/opt/gcc/lib/gcc/10/libquadmath.0.dylib

It might help because there is no /usr/lib/libSystem.B.dylib on Big Sur 11.1 (so this file is not used I suppose), but instead it gives me a new error:

OSError                                   Traceback (most recent call last)
<ipython-input-7-21ad9f6d803b> in <module>
     12 try:
---> 13     mylib = ctypes.CDLL(mylib_path)
     14 except OSError:

~/opt/anaconda3/lib/python3.7/ctypes/__init__.py in __init__(self, name, mode, handle, use_errno, use_last_error)
    363         if handle is None:
--> 364             self._handle = _dlopen(self._name, mode)
    365         else:

OSError: dlopen(mylib.dylib, 6): Library not loaded: /usr/local/opt/gcc/lib/gcc/10/libgcc_ext.10.4.dylib
  Referenced from: /usr/local/opt/gcc/lib/gcc/10/libquadmath.0.dylib
  Reason: no suitable image found.  Did find:
    /usr/local/opt/gcc/lib/gcc/10/libgcc_ext.10.4.dylib: mach-o, but wrong filetype
    /usr/local/Cellar/gcc/10.2.0/lib/gcc/10/libgcc_ext.10.4.dylib: mach-o, but wrong filetype

4. I also tried to brew reinstall gcc, before this action there was /usr/local/libSystem.B.dylib instead of flat namespace in the actual issue.

5. There are some related issues: scipy, scipy.special, scipy._fblas, gdal2. Their solutions do not help, because usually, they are about re-installing the packages, and here I have my own package.

6. Eventually, I tried to set CC=clang/g++/g++-10 when building with bazel. Unfortunately, it did not work.

Any suggestions and thoughts would be highly appreciated. Thank you in advance 🙏

Answer 1

Following @n. 'pronouns' m. advice from the comments, I tried to link libgcc_s instead of libSystem:

install_name_tool -change "/usr/lib/libSystem.B.dylib" "/usr/local/opt/gcc/lib/gcc/10/libgcc_s.1.dylib" mylib.dylib

It gave me another error: Symbol not found: ___emutls_get_address from libopenblas. I googled and found this SO answer, and did:

brew link --overwrite gcc

Then the only thing I did is rebuilt the mylib.dylib with bazel with exact the same rules as earlier and it worked! Now the library loads in python without any errors. Thank you so much.