[llvm-commits] [llvm] r57846 - in /llvm/trunk: include/llvm/System/Memory.h lib/System/Unix/Memory.inc lib/System/Win32/Memory.inc lib/Target/ARM/ARMJITInfo.cpp

[Jim Grosbach]

On Oct 21, 2008, at 9:24 AM, Evan Cheng wrote:
>>> Is this code Mac OS X specific? Is "push" accepted by all the
>>> assemblers?
>>>
>>
>> It's standard, but relatively recent (sometime in the last few years,
>> depending on toolchain) for the mnemonic to be recognized in ARM
>> state. How concerned are we about older assemblers?
>
> I think we should use mnemonic that are as widely accepted as
> possible. I believe the original author did test the callback routine
> on his target. We should be careful not to break it.
>

Sounds good. I'll tweak it this morning.

> Having the stub making a system
> call to change memory privilege just seem icky to me. My basic idea is
> to allocate a chunk RX memory for code (like what's being done now)
> and a chunk of RW memory for data and anything that's going to be
> changed during execution (i.e. putting addresses of lazily compiled
> functions there). This will require a larger scale rewrite so it's not
> something that should be planned for the near future.
>

No disagreement here. I played with that for a while, but it gets  
pretty hairy, especially with lazy compilation. I backed off and chose  
to get it working first, even with the ugly syscalls. Not that in re- 
writing the stub we're writing not just an address, but an  
instruction, for example. The meta-data for the memory blocks are  
another tricky spot.

Doing something about this stuff would require a new, or at least  
significantly re-worked, JIT Memory Manager, possibly one that's  
target specific. As you say, a pretty significant refactoring and  
probably outside the scope of what we want to look at right now.