Unexpected reloc type 0x00020001 on CentOS7

[nehaljwani]

Steps to reproduce:

$ sudo docker run -v /path/to/mold/install:/root/prefix --rm -it --net host centos:7 /bin/bash

# Install dependencies
$ yum install gcc-c++ python3-devel -y

# Source code for python3 module
$ cat <<EOF > Py_module.cc 
#include <Python.h>

static struct PyModuleDef moduledef = {
    PyModuleDef_HEAD_INIT, /* m_base */
    "pycore",              /* m_name */
    nullptr,               /* m_doc */
    -1,                    /* m_size */
    nullptr,               /* m_methods */
    nullptr,               /* m_slots */
    nullptr,               /* m_traverse */
    nullptr,               /* m_clear */
    nullptr                /* m_free */
};

PyMODINIT_FUNC PyInit_pycore(void)
{
    PyObject* module = PyModule_Create(&moduledef);
    if (module == nullptr)
    {
        return nullptr;
    }

    return module;
}
EOF

# Compile the object file
$ g++ -I/usr/include/python3.6m -fPIC -std=c++11 -o pycore.o -c Py_module.cc

# Generate shared library using mold
$ g++ -B$PWD/prefix/bin -shared -Wl,-soname,pycore.so -o pycore.so pycore.o
$ readelf -p .comment pycore.so 

String dump of section '.comment':
  [     0]  mold 0.9.6 (06c237838c9bde07820f0ad38c5421536dad4701; compatible with GNU ld and GNU gold)
  [    5b]  GCC: (GNU) 4.8.5 20150623 (Red Hat 4.8.5-44)

# Try to import it (fails!)
$ python3
Python 3.6.8 (default, Nov 16 2020, 16:55:22) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pycore
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: /pycore.so: undefined symbol: libstdc++.so.6

# Link and import it without mold (success!)
$ g++ -shared -Wl,-soname,pycore.so -o pycore.so pycore.o
$ python3
Python 3.6.8 (default, Nov 16 2020, 16:55:22) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pycore
>>> 

# Link again with mold, import with python2 just for fun (better error)
$ g++ -B$PWD/prefix/bin -shared -Wl,-soname,pycore.so -o pycore.so pycore.o
$ python
Python 2.7.5 (default, Nov 16 2020, 22:23:17) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import pycore
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: ./pycore.so: unexpected reloc type 0x00020001
>>> 

# Version of ld.so
$ rpm -qf /lib64/ld-linux-x86-64.so.2 
glibc-2.17-324.el7_9.x86_64

[nehaljwani]

Attaching statically linked mold (for use on glibc2.12+ , kernel 2.6.32+) for convenience: mold.gz

[rui314]

Thank you for your report! It looks dlopen() fails with any mold-generated shared object files on CentOS 7. Investigating...

[rui314]

I believe the above change fixed the issue. Could you verify?

[nehaljwani]

Verified. Thank you for the prompt fix!