Re: [Gems-users] memory accesses

[Dan Gibson <degibson@xxxxxxxx>]

I would not be entirely surprised if the seg fault occurs BEFORE ruby 
receives the request.
Your address 0x7FFF00000000 is undergoing translation. It becomes a TLB 
miss, which quickly is realized as a segfault because (virtual address) 
0x7FFF00000000 is not mapped in your virtual address space. Since 
physical address 0x7FFF00000000 is never accessed (as nothing ever 
translates to that address), your printf's in Ruby are never invoked.
Regards,
Dan

Sevin Fide wrote:

> Hello All,
>
> I've got a device module in Simics 2.2.19 which is
> mapped at 0x7FFF00000000. I'd like to log the accesses
> to this device in Ruby. Here is a code snippet from my
> test program:
>
> #define LOCATION 0x7FFF00000000ULL
>
>  int offset = 0;
>  volatile unsigned long long *myDevice = (unsigned
> long long *) LOCATION;
>
>  printf("Reading offset %d\n", offset);
>  printf("myDevice[%d]=%d\n", offset,
> myDevice[offset]);  
>
> I put some printf statements (see below) in
> module/ruby.c - ruby_operate and simics/commands.C -
> memorytracer_possible_cache_miss and
> memorytracer_observe_memory.
>
> if (mem_trans->s.physical_address ==
> 0x7FFF00000000ULL)
> print something
>
> Before I get anything printed in Simics console, I get
> a segmentation fault on the simulated host. I'd
> presume the memory request would be sent to Ruby first
> and then seg fault as the location is out of the
> assigned address range. If that's not the case, then
> Ruby never receives the access request to my LOCATION.
> Could you please help me with understanding the steps
> in memory accesses?
>
> Thanks a lot!
>
> Sevin
>
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