Re: JIT test crash

[Michael Goffioul]

On Thu, Aug 2, 2012 at 8:54 PM, Michael Goffioul <address@hidden> wrote:

On Thu, Aug 2, 2012 at 6:42 PM, Max Brister <address@hidden> wrote:

On Thu, Aug 2, 2012 at 8:36 AM, Michael Goffioul

<address@hidden> wrote:
> On Thu, Aug 2, 2012 at 1:57 PM, Max Brister <address@hidden> wrote:

>>[snip] 

>>
>> The output with OCTAVE_JIT_DEBUG looks correct to me.
>>
>> I have attached the patch for llvm 3.1.
>
>
> I applied it, but it didn't change anything (the generated assembly looks
> exactly the same). If I'm reading this [1] correctly (XF86SubTarget
> constructor), the stack alignment was already set to 4 anyway. And in [2],
> in X86_32TargetMachine constructor, the native stack alignment is also
> specified on 4 bytes (trailing "-S32" at line 45).
>
> Michael.
>
> [1]
> https://github.com/earl/llvm-mirror/blob/master/lib/Target/X86/X86Subtarget.cpp
> [2]
> https://github.com/earl/llvm-mirror/blob/master/lib/Target/X86/X86TargetMachine.cpp

Actually, that makes sense. In order to use the sse instruction, we
really want the stack to 16 byte aligned I think. Can you try changing
the stack alignment to 16 bytes instead of 4?

No luck. I've modified your patch to read:

opts.StackAlignmentOverride = 16

For your information, I've attached the generated assembly for the 4-bytes and 16-bytes case. The code still crashes, but at an earlier location. Now it crashes at the MOVAPD call (address 02D300BC). If you compare with the 4-bytes case, the latter uses MOVUPD instead, so it doesn't crash. Also if you compare the 2 files, you see that in the 16-bytes case, all stack offsets are multiple of 16 bytes, but I don't see any code to realign the stack on a 16-bytes boundary.

The bottom line is: within the generated code, the stack is kept aligned on 16-bytes, but as there's no forced realignment, it entirely depends on the stack alignment on function entry.

Any update, ideas or suggestions?

Michael.