[BUG]: Crash due to invalid free during cleanup, if any enum is registerd, due to attempting to `free` a string literal

[adalisk-emikhaylov]

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What version (or hash if on master) of pybind11 are you using?

4f81a12

Problem description

Importing this and then exiting Python causes a crash at

pybind11/include/pybind11/pybind11.h

Line 824 in 4f81a12

std::free(const_cast<char *>(arg.name));

arg.name is "self", and it appears to be a string literal instead of a malloced string.

Said literal is assigned to it at

pybind11/include/pybind11/attr.h

Line 494 in 4f81a12

r->args.emplace_back("self", nullptr, handle(), /*convert=*/true, /*none=*/false);

Editing that function to malloc the string seems to fix the crash.

I've bisected this, the offending commit is 1b7aa0b

---

I'm not sure if it matters, but I'm on CPython 3.10 on Ubuntu 22.04.

Reproducible example code

#include <pybind11/pybind11.h>

enum E {};

PYBIND11_MODULE(example, m)
{
    pybind11::enum_<E> e(m, "E");
}

Is this a regression? Put the last known working version here if it is.

15d9dae

[adalisk-emikhaylov]

@timohl Friendly ping, seems to be introduced by your commit.

[timohl]

Can you also share the python code that causes the crash?
Your reproducible code looks so minimal, that I think there must be something else going on.
My commit is a year old and this looks like a basic enum binding, so I think many others would have noticed this before.

Btw, py::enum_ is deprecated, so if you are looking for a quick replacement, try py::native_enum.

[adalisk-emikhaylov]

Just import example and then exiting Python. I just tested this on a different OS (this time Arch), and it reproduces here too.

Paste the code into 1.cpp, clone pybind into the current directory, and run

g++ 1.cpp `python3-config --libs --cflags` -shared -o example.so -fPIC -Ipybind11/include
python3 -c 'import example'

This gives me

free(): invalid pointer
Aborted                    (core dumped) python3 -c 'import example'

My commit is a year old

Oh, I didn't realize it's 2026 already. 🙂