Unreachable code
Description of problem:
There is always a false condition in the function `alloc_code_gen_buffer_splitwx_memfd` in the file `tcg/region.c`. If `buf_rw == NULL` we go to the mark __fail__:

https://gitlab.com/qemu-project/qemu/-/blob/master/tcg/region.c?ref_type=heads#L580-L583

But the value of `buf_rx` is __`MAP_FAILED`__:

https://gitlab.com/qemu-project/qemu/-/blob/master/tcg/region.c?ref_type=heads#L577

And this line will never be reached:

https://gitlab.com/qemu-project/qemu/-/blob/master/tcg/region.c?ref_type=heads#L601

Found by Linux Verification Center (portal.linuxtesting.ru) with SVACE.

Author A. Voronin.