Segmentation fault with MinGW-w64 due to `-lucrt`

The minimal reproducer:

``` cython
# hello.pyx
from libc.stdio cimport printf

def say_hello():
    printf("Hello %d world!\n", 42)
```

``` python
# setup.py
from setuptools import setup
from Cython.Build import cythonize

setup(
    ext_modules=cythonize("hello.pyx"),
)
```

Build and run it in msys2 environment:

``` shell
$ python -c 'import sys; print(sys.version)'
3.10.9 (tags/v3.10.9:1dd9be6, Dec  6 2022, 20:01:21) [MSC v.1934 64 bit (AMD64)]

$ CC=/mingw64/bin/gcc python setup.py build_ext -i
...

$ python -X dev -c 'import hello; hello.say_hello()'
Windows fatal exception: access violation

Current thread 0x0000140c (most recent call first):
  File "<string>", line 1 in <module>
zsh: segmentation fault  python -X dev -c 'import hello; hello.say_hello()'
```

This is because mingw64-gcc links msvcrt by default [[1]](https://www.msys2.org/docs/environments/), but distutils links ucrt, which causes incompatibility.

It was introduced in #41 and was reported in #109 a year ago. Simply removing `"ucrt"` can fix this.

-----

For the relationship between msvcrt and ucrt on MinGW-w64, [this post](https://sourceforge.net/p/mingw-w64/mailman/message/36621319/) talked about it clearly.

**tl; dr: `-lucrt` never works for gcc.** On msys2 mingw64 environment, it causes segfault; On msys2 ucrt64 environment, it's a noop. It's not msys2-specific, in fact all MinGW-w64 gcc builds are the same. I have tested on w64devkit and cygwin, the results are at the bottom.

In MinGW-w64, `libmsvcrt.a` is just an alias, which varies with `--with-default-msvcrt` in the configuration step. By default, it's `msvcrt`, which means `libmsvcrt.a` is an alias for `libmsvcrt-os.a`. Most MinGW-w64 builds are configured like this, so does msys2 mingw64 environment.[[2]](https://github.com/msys2/MINGW-packages/blob/1a329c6a0a6e7ca577c93f74ef52fa65012c2462/mingw-w64-crt-git/PKGBUILD#L73) In this case, the compiled executable will dynamically link to `msvcrt.dll`. `--with-default-msvcrt` can also be set to `ucrt`, which is msys2 ucrt64 environment does, means `libmsvcrt.a` is an alias for `libucrt.a`, and the compiled executable will dynamically link to `ucrtbase.dll`.

``` shell
$ sha256sum /mingw64/lib/lib{msvcrt*,ucrt.a}
b7c701c34572d672f19ddb6dbd4d28c5f8ea9d08391184a76edc65b7ca2e3811 */mingw64/lib/libmsvcrt.a
b7c701c34572d672f19ddb6dbd4d28c5f8ea9d08391184a76edc65b7ca2e3811 */mingw64/lib/libmsvcrt-os.a
3385e765d960fa88a833e5be96a07d8ea1fc4772de5992576e7f7f4eff952da1 */mingw64/lib/libucrt.a

$ sha256sum /ucrt64/lib/lib{msvcrt*,ucrt.a}
3bc0a7a52d0b45c39f2b399e4b5843320246bb6c136c78dc738d8143a7d7664c */ucrt64/lib/libmsvcrt.a
988e3f3f60af32dad4991d05ac4d46e55bfee4b257ea6bb38b38b91d1d57bd77 */ucrt64/lib/libmsvcrt-os.a
3bc0a7a52d0b45c39f2b399e4b5843320246bb6c136c78dc738d8143a7d7664c */ucrt64/lib/libucrt.a
```

In both cases, libgcc is implicitly linked with `-lmsvcrt` (remember, it's an alias).

``` shell
$ gcc -dumpspecs | grep -B 1 msvcrt
*libgcc:
%{mthreads:-lmingwthrd} -lmingw32      %{static|static-libgcc:-lgcc -lgcc_eh}  %{!static:    %{!static-libgcc:      %{!shared:        %{!shared-libgcc:-lgcc -lgcc_eh}        %{shared-libgcc:-lgcc_s -lgcc}       }      %{shared:-lgcc_s -lgcc}     }   }     -lmoldname -lmingwex %{!mcrtdll=*:-lmsvcrt} %{mcrtdll=*:-l%*} -lkernel32
```

So, on msys2 mingw64 environment, libgcc is always linked to msvcrt.dll. If `-lucrt` is passed, the C program will link to ucrtbase.dll, which is incompatible with libgcc and will cause segmentation faults. On msys2 ucrt64 environment, obviously, ucrt is linked implicitly, so it's not necessary to pass `-lucrt`.

For gcc, if you want the program to link to ucrt properly on a MinGW-w64 `--with-default-msvcrt=msvcrt` environment, the only way is to dump gcc's specs and modify it (by `gcc -dumpspecs`, which has been metioned in that post). [imba-tjd/mingw64ccompiler is doing the right thing.](https://github.com/imba-tjd/mingw64ccompiler/blob/b78a5baba0ddf6121044174d65774cdbe66b4b46/mingw64ccompiler.py#L71-L77)

By the way, even the simplest C hello world compiled with `gcc -lucrt` behaves the same here.

-----

<details>

<summary>click to expand</summary>

First, generate `hello.c` from `hello.pyx` with cython:

``` shell
$ cython -3 hello.pyx
```

## msys2 mingw64 prefix

### without `-lucrt`

``` shell
$ /mingw64/bin/gcc -shared "-IC:/Program Files/Python310/include" hello.c "-LC:/Program Files/Python310" "-LC:/Program Files/Python310/Libs" -lpython310 -o hello.pyd

$ python -X dev -c 'import hello; hello.say_hello()'
Hello 42 world!

$ objdump -p hello.pyd | grep 'DLL Name'
        DLL Name: KERNEL32.dll
        DLL Name: msvcrt.dll
        DLL Name: python310.dll
```

### with `-lucrt`

``` shell
$ /mingw64/bin/gcc -shared "-IC:/Program Files/Python310/include" hello.c -lucrt "-LC:/Program Files/Python310" "-LC:/Program Files/Python310/Libs" -lpython310 -o hello.pyd

$ python -c 'import hello; hello.say_hello()'
zsh: segmentation fault  python -c 'import hello; hello.say_hello()'

$ objdump -p hello.pyd | grep 'DLL Name'
        DLL Name: KERNEL32.dll
        DLL Name: msvcrt.dll
        DLL Name: api-ms-win-crt-environment-l1-1-0.dll
        DLL Name: api-ms-win-crt-heap-l1-1-0.dll
        DLL Name: api-ms-win-crt-runtime-l1-1-0.dll
        DLL Name: api-ms-win-crt-stdio-l1-1-0.dll
        DLL Name: api-ms-win-crt-time-l1-1-0.dll
        DLL Name: python310.dll
```

## msys2 ucrt64 prefix

### without `-lucrt`

``` shell
$ /ucrt64/bin/gcc -shared "-IC:/Program Files/Python310/include" hello.c "-LC:/Program Files/Python310" "-LC:/Program Files/Python310/Libs" -lpython310 -o hello.pyd

$ python -c 'import hello; hello.say_hello()'
Hello 42 world!

$ objdump -p hello.pyd | grep 'DLL Name'
        DLL Name: KERNEL32.dll
        DLL Name: api-ms-win-crt-environment-l1-1-0.dll
        DLL Name: api-ms-win-crt-heap-l1-1-0.dll
        DLL Name: api-ms-win-crt-runtime-l1-1-0.dll
        DLL Name: api-ms-win-crt-stdio-l1-1-0.dll
        DLL Name: api-ms-win-crt-string-l1-1-0.dll
        DLL Name: api-ms-win-crt-time-l1-1-0.dll
        DLL Name: python310.dll
```

### with `-lucrt`

``` shell
$ /ucrt64/bin/gcc -shared "-IC:/Program Files/Python310/include" hello.c -lucrt "-LC:/Program Files/Python310" "-LC:/Program Files/Python310/Libs" -lpython310 -o hello.pyd

$ python -c 'import hello; hello.say_hello()'
Hello 42 world!

$ objdump -p hello.pyd | grep 'DLL Name'
        DLL Name: KERNEL32.dll
        DLL Name: api-ms-win-crt-environment-l1-1-0.dll
        DLL Name: api-ms-win-crt-heap-l1-1-0.dll
        DLL Name: api-ms-win-crt-runtime-l1-1-0.dll
        DLL Name: api-ms-win-crt-stdio-l1-1-0.dll
        DLL Name: api-ms-win-crt-string-l1-1-0.dll
        DLL Name: api-ms-win-crt-time-l1-1-0.dll
        DLL Name: python310.dll
```

## w64devkit 1.17.0

- home page: https://github.com/skeeto/w64devkit
- download: https://github.com/skeeto/w64devkit/releases/download/v1.17.0/w64devkit-mini-1.17.0.zip

``` shell
$ sha256sum x86_64-w64-mingw32/lib/libmsvcrt.a x86_64-w64-mingw32/lib/libmsvcrt-os.a x86_64-w64-mingw32/lib/libucrt.a
e136d6158cf573080aba84c6a910824cc97ba00a966372af06a3e799c0ed5500  x86_64-w64-mingw32/lib/libmsvcrt.a
e136d6158cf573080aba84c6a910824cc97ba00a966372af06a3e799c0ed5500  x86_64-w64-mingw32/lib/libmsvcrt-os.a
931553676e70104c98e95bcbfd063f1ab24ab9a1ab5cc7d0161c686940550e38  x86_64-w64-mingw32/lib/libucrt.a
```

### without `-lucrt`

``` shell
$ gcc -shared "-IC:/Program Files/Python310/include" hello.c "-LC:/Program Files/Python310" "-LC:/Program Files/Python310/Libs" -lpython310 -o hello.pyd

$ python -c 'import hello; hello.say_hello()'
Hello 42 world!

$ objdump -p hello.pyd | grep 'DLL Name'
        DLL Name: KERNEL32.dll
        DLL Name: msvcrt.dll
        DLL Name: python310.dll
```

### with `-lucrt`

``` shell
$ gcc -shared "-IC:/Program Files/Python310/include" hello.c -lucrt "-LC:/Program Files/Python310" "-LC:/Program Files/Python310/Libs" -lpython310 -o hello.pyd

$ python -c 'import hello; hello.say_hello()'
zsh: segmentation fault  python -c 'import hello; hello.say_hello()'

$ objdump -p hello.pyd | grep 'DLL Name'
        DLL Name: KERNEL32.dll
        DLL Name: msvcrt.dll
        DLL Name: api-ms-win-crt-environment-l1-1-0.dll
        DLL Name: api-ms-win-crt-heap-l1-1-0.dll
        DLL Name: api-ms-win-crt-runtime-l1-1-0.dll
        DLL Name: api-ms-win-crt-stdio-l1-1-0.dll
        DLL Name: api-ms-win-crt-time-l1-1-0.dll
        DLL Name: python310.dll
```

## cygwin mingw64-gcc

- home page: https://cygwin.com/
- package name: `mingw64-x86_64-gcc-core`
- package version: `11.3.0-1`

``` shell
$ sha256sum /usr/x86_64-w64-mingw32/sys-root/mingw/lib/lib{msvcrt*,ucrt.a}
da55e191ae4ef503db42d36e400ca3dcc8f66e608f762e6a725aca9441088c38 */usr/x86_64-w64-mingw32/sys-root/mingw/lib/libmsvcrt.a
da55e191ae4ef503db42d36e400ca3dcc8f66e608f762e6a725aca9441088c38 */usr/x86_64-w64-mingw32/sys-root/mingw/lib/libmsvcrt-os.a
672f28150c81fb070f5688334f6f2f011f7120ab79f857cc2ccd9ac21e8f49bb */usr/x86_64-w64-mingw32/sys-root/mingw/lib/libucrt.a
```

### without `-lucrt`

``` shell
$ x86_64-w64-mingw32-gcc -shared "-IC:/Program Files/Python310/include" hello.c "-LC:/Program Files/Python310" "-LC:/Program Files/Python310/Libs" -lpython310 -o hello.pyd

$ python -c 'import hello; hello.say_hello()'
Hello 42 world!

$ objdump -p hello.pyd | grep 'DLL Name'
        DLL Name: KERNEL32.dll
        DLL Name: msvcrt.dll
        DLL Name: python310.dll
```

### with `-lucrt`

``` shell
$ x86_64-w64-mingw32-gcc -shared "-IC:/Program Files/Python310/include" hello.c -lucrt "-LC:/Program Files/Python310" "-LC:/Program Files/Python310/Libs" -lpython310 -o hello.pyd

$ python -c 'import hello; hello.say_hello()'
zsh: segmentation fault  python -c 'import hello; hello.say_hello()'

$ objdump -p hello.pyd | grep 'DLL Name'
        DLL Name: KERNEL32.dll
        DLL Name: msvcrt.dll
        DLL Name: api-ms-win-crt-environment-l1-1-0.dll
        DLL Name: api-ms-win-crt-heap-l1-1-0.dll
        DLL Name: api-ms-win-crt-runtime-l1-1-0.dll
        DLL Name: api-ms-win-crt-stdio-l1-1-0.dll
        DLL Name: api-ms-win-crt-time-l1-1-0.dll
        DLL Name: python310.dll
```

</details>

-----

CC @imba-tjd 

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Segmentation fault with MinGW-w64 due to `-lucrt` #196

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Uh oh!

Segmentation fault with MinGW-w64 due to -lucrt #196

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msys2 mingw64 prefix

without -lucrt

with -lucrt

msys2 ucrt64 prefix

without -lucrt

with -lucrt

w64devkit 1.17.0

without -lucrt

with -lucrt

cygwin mingw64-gcc

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Segmentation fault with MinGW-w64 due to `-lucrt` #196

without `-lucrt`

with `-lucrt`

without `-lucrt`

with `-lucrt`

without `-lucrt`

with `-lucrt`

without `-lucrt`

with `-lucrt`