[llvm-dev] Memory mapping assumptions in RuntimeDyld

[Lang Hames via llvm-dev]

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
>
> IBM Deutschland GmbH
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