>> Come on, having me preparing bootable CF card image for a gizmo I'm not
>> familiar with is unrealistic. Don't you have anything you can compile
>> 10-lines C code and some assembler to add to?
>
> Well you mentioned tests on x86 in your paper, I thought you
> do have some minimal test setup ready for it.
No. For following reason. Originally idea was to attempt to gather "OS
noise". I mean entropy would come from interrupts, interaction with say
DMA, etc. Therefore no explicit attempts to perform the experiment
"outside" OS were made. Besides it would be impossible for me to set it
up in most cases (because normally access is remote non-privileged). But
having observed it in OS-free environment made me wonder...
> No problem to compile
> something here, I just do not want to run it under an operating
> system that sets the hardware who knows how (disabling
> ints is not enough if something is trying to do a DMA
> or something).
Arguably OS only adds entropy, and it appears to be rather little on
idle system. So just running it under low load is good enough.
>> "but ARM" might be too "weak" requirement. OPENSSL_instrument_bus is
>> dependent on presence of clflush instruction which is normally available
>> with SSE2. Does your Geode support it? It's exposed in /proc/cpuinfo
>> under Linux. And of course rdtsc.
>
> Yes, the processor does have tsc and clflush.
>
> FWIW on the ARMs I have I am able to manipulate/disable cache
> (on some there is no cache) and to read a counter ticking
> synchronously with the processor clock.
I know that newer ARM even allows you to make tick counter accessible to
user-land and there is even a way to flush cache line, but it's all
privileged operations and I work under assumption that code runs in
user-land. Therefore OPENSSL_instrument_bus is reduced to return 0; on ARM.
> What data do you need? OPENSSL_instrument_bus with 128k probes
> taken?
Yes, as simple as
#include <stdio.h>
#define N (128*1024)
main()
{ int i,n;
static int arr[N];
memset(arr,0,sizeof(arr));
n=OPENSSL_instrument_bus(arr,N);
for (i=0;i<n;i++)
printf("%d\n",arr[i]);
}
would do. I also collect for n=OPENSSL_instrument_bus2(arr,N,0);...
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