[LLVMdev] MallocInst/CallInst bitcast,

[Chris Lattner]

On Oct 16, 2009, at 11:21 AM, Daniel Waterworth wrote:

> Thanks very much. I only have one more question, (hopefully), which  
> is, is there a better way of finding the direction of stack growth  
> other than:

That's a somewhat reasonable, but fragile way to go.  Make sure to  
mark StackCmp with attribute(noinline).  Don't be too surprised if it  
doesn't work on some compiler.  I don't know a better way to do it  
though.

-Chris

>
> static bool StackCmp(void *ptr) {
>   volatile int a;
>   return (void *)&a > ptr;
> }
>
> bool FindStackDirection() {
>   volatile int a;
>   return StackCmp((void *)&a);
> }
>
> Preferably one which isn't destroyed by optimization.
>
> Thanks again,
>
> Daniel
>
> 2009/10/16 Chris Lattner <clattner at apple.com>
>
> On Oct 16, 2009, at 4:43 AM, Daniel Waterworth wrote:
>
>> Never mind, I used ExecutionEngine's InstallLazyFunctionCreator and  
>> DisableSymbolSearching to cause malloc and free calls to be handled  
>> by my logging functions. Sorry for the unnecessary list mail.
>
> No problem, this is a better way to go.  The MallocInst and FreeInst  
> instructions are about to be removed from LLVM IR.  Malloc and free  
> will be represented normal 'call' instructions.
>
>> Is it possible to find out the size and beginning pointer of the  
>> current stack frame, from a function operating outside of the  
>> virtual machine, but called by a function within it?
>
> I don't think so.  Typically, applications that need this sort of  
> thing get the address of the function and then do a fuzzy  
> disassembly of the prolog.
>
> -Chris
>
>>
>> Thanks,
>>
>> Daniel
>>
>> 2009/10/16 Daniel Waterworth <da.waterworth at googlemail.com>
>> Hello,
>>
>> I'm writing a virtual machine that functions as a sandbox based on  
>> llvm. In order to prevent programs from accessing memory that has  
>> not been allocated to them, I want to replace calls to malloc and  
>> free with calls to a logged functions that will record the memory  
>> that is being allocated to the program. Is it possible to cast/ 
>> convert a MallocInst or FreeInst to a CallInst?
>>
>> Thanks,
>>
>> Daniel
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20091016/9bdd1ac6/attachment.html>