[LLVMdev] [PATCH] Fix for bug in JIT exception table allocation (no test yet)

[Michael Muller]

Eric Christopher wrote:
> 
> On Aug 21, 2012, at 2:12 PM, Michael Muller <mmuller at enduden.com> wrote:
> 
> > 
> > Hi, I found a bug in the code that generates exception tables, I've attached
> > what I think is the correct fix.
> > 
> > When you run out of space writing to a buffer, the buffer management code
> > simply stops writing at the end of the buffer.  It is the responsibility of
> > the caller to verify that it has stayed in bounds and perform a retry with
> > a larger memory estimate if not.  The function writing code does this, but
> > the exception table code following it does not.  The end result is that
> > exception table pointers can get registered pointing to invalid data, causing
> > seg-faults when an exception is thrown.
> > 
> > I haven't implemented a test case that reproduces the problem, but I will do
> > so.  (I've verified the problem and the fix in the scope of a much larger
> > system) I'm open to suggestions as to how best to test it, I'm currently
> > thinking of trying to create a highly contrived situation to force exception
> > tables to be written at the end of a buffer that won't be long enough.
> 
> I'm actually somewhat curious at this point why it doesn't emit the tables before
> deciding it's done with the function. That'd make it possible to move all of
> the eh table code earlier in the method and use retryWith... instead of the loop.

It looks like it might be using a different slab for the function, though I'm
not quite sure why.  I'll investigate further when I get back to it.  Making
it part of the function's "transaction" seemed cleaner to me as well.

> 
> -eric
> 


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