[llvm-dev] Memory mapping assumptions in RuntimeDyld

[Kai Peter Nacke via llvm-dev]

Thanks! That explains it.

Lang Hames <lhames at gmail.com> wrote on 02.10.2020 20:04:15:

> From: Lang Hames <lhames at gmail.com>
> To: Kai Peter Nacke <kai.nacke at de.ibm.com>
> Cc: LLVM Developers Mailing List <llvm-dev at lists.llvm.org>
> Date: 02.10.2020 20:04
> Subject: [EXTERNAL] Re: Memory mapping assumptions in RuntimeDyld
> 
> Hi Kai, Is this true, or do I miss something? Sorry if this is a 
> trivial question!...  
> 
> This Message Is From an External Sender
> 
> This message came from outside your organization.
> 
> Hi Kai,

> Is this true, or do I miss something? Sorry if this is a trivial 
question!
> 
> That's correct, and not at all. :)
> 
> RuntimeDyld does not support the small code model: It requires code 
> to be compiled with the large code model so that references can 
> cover the entire address space.
> 
> There is a newer JIT linker, JITLink, which removes this 
> restriction. There is a MachO implementation for AArch64, but no ELF
> or COFF implementation yet. Once that is written we should be able 
> to support small code model in the JIT.
> 
> -- Lang.
> 
> On Fri, Oct 2, 2020 at 10:02 AM Kai Peter Nacke <kai.nacke at de.ibm.com> 
wrote:
> Hi!
> 
> Implementing the Memory::allocateMappedMemory() function on z/OS, I see 
a 
> failure in the AArch64 COFF test case.
> The test case has 3 sections. For each section, 
> Memory::allocateMappedMemory() is called to reserve memory.
> If the distance between the pointers gets too large, then the test case 
> fails. It can be reliable produced with
> a distance of 1MB between the pointers. An easy way to simulate this is 
to 
> increase the number of memory bytes
> requested by 1MB (e.g. adding NumBytes += (1<<20); at begin of the 
> method). Then the check if a relocation is correctly
> resolved fails.
> My current understanding is that the kernel is more or less free to 
choose 
> the address of the mapped memory, so this
> situation can arise. Is this true, or do I miss something? Sorry if this 

> is a trivial question!
> 
> Best regards,
> Kai
> 
> Kai Nacke
> IT Architect
> 
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