[LLVMdev] mmap and vm_protect on ARM+Apple systems

[Kaylor, Andrew]

Hi,

Can anyone tell me something about mmap and vm_protect on ARM+Apple systems?

I'm working on a new memory manager implementation for MCJIT and I want to replace calls to Memory::AllocateRWX with calls to Memory::allocateMappedMemory, possibly still with the RWX flags.  However, looking at the Memory::AllocateRWX implementation I see that it's jumping through some hoops in the case where both '__APPLE__' and '__arm__' are defined.

I want to handle two cases:


1)      Allocate memory as RWX, copy JITed code into it and execute it without ever touching the permissions again.

2)      Allocate memory as RW, copy JITed code into it and then set the permissions to RX before executing.

This seems pretty straight-forward with the functions that use mmap and mprotect, but the AllocateRWX implementation leads me to believe that won't work in the ARM+Apple case.  I read some vm_protect documentation, but I can't quite reconcile it with the AllocateRWX implementation.

My goal is to make sure the Memory::allocateMappedMemory and Memory::protectMappedMemory functions will work everywhere.

Any suggestions?

Thanks,
Andy

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