[Bug 1914849] Re: mprotect fails after MacOS 11.2 on arm mac

[hikalium]

I hit the same problem and did some initial investigation with
Toshifumi.

Here is a more exhaustive test program I wrote based on the post on the
Apple Developer Forums and the result shows that very interesting
behavior of mmap and mprotect since macOS 11.2.

https://gist.github.com/hikalium/75ae822466ee4da13cbbe486498a191f

I and my friend confirmed that all mmap & following mprotect calls with
any protection bit combinations are succeeded up to 11.1 on M1 Mac but
starting from 11.2 mprotect starts failing if we call mmap with
PROT_WRITE + PROT_EXEC. (Surprisingly, mmap itself is not failing even
on those patterns.)

It looks like the allocation of code gen buffer in QEMU uses this combination 
at mmap call:
https://github.com/qemu/qemu/blob/master/accel/tcg/translate-all.c#L1294

So maybe we need to specify PROT_NONE instead on the initial mmap and
change it appropriately afterwards to make it working on M1 Mac after
11.2.

(We tried to fix it but we have no sufficient knowledge about tcg...
Could you take a look into it?)

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https://bugs.launchpad.net/bugs/1914849

Title:
  mprotect fails after MacOS 11.2 on arm mac

Status in QEMU:
  New

Bug description:
  I got the following error when I ran qemu on arm mac(MacOS 11.2).

  ```
  $ ./qemu-system-x86_64
  qemu-system-x86_64: qemu_mprotect__osdep: mprotect failed: Permission denied
  **
  ERROR:../tcg/tcg.c:844:tcg_region_init: assertion failed: (!rc)
  Bail out! ERROR:../tcg/tcg.c:844:tcg_region_init: assertion failed: (!rc)
  [1]    34898 abort      ./qemu-system-x86_64
  ```

  I tested the same version of qemu on intel mac(MacOS 11.2), but it
  works fine.

  And my friend told me that they did not have this error with MacOS
  11.1.

  So, I think it is CPU architecture or an OS version dependent error.

  
  Environment:

  Qemu commit id: d0dddab40e472ba62b5f43f11cc7dba085dabe71
  OS: MacOS 11.2(20D64)
  Hardware: MacBook Air (M1, 2020)

  
  How to build:

  ```
  mkdir build/
  cd build/
  ../configure --target-list=aarch64-softmmu,x86_64-softmmu
  make
  ```

  
  How to reproduce:

  ```
  ./qemu-system-x86_64
  ```

  
  Error message:

  ```
  $ ./qemu-system-x86_64
  qemu-system-x86_64: qemu_mprotect__osdep: mprotect failed: Permission denied
  **
  ERROR:../tcg/tcg.c:844:tcg_region_init: assertion failed: (!rc)
  Bail out! ERROR:../tcg/tcg.c:844:tcg_region_init: assertion failed: (!rc)
  [1]    34898 abort      ./qemu-system-x86_64
  ```

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