Re: [uml-devel] Memory corruption/errors?

[Peter <peter.spamcatcher@rimuhosting.com>]

I don't run TT mode UMLs.  So, no I haven't tried that.

I don't know about the sighandler.  The program runs as it was listed. 
It is running on a 'regular' server (Debian, and/or WBL3) with other 
processes running.  And the host servers happen to be running other 
UMLs.  I don't know if that information helps.  (i.e. can a sighandler 
in another process on the UML or on the host cause this problem?)

I'd be happy to try out a skas patch - preferably if it just applied to 
the guest ;)  To see if it fixes things or not.

Regards, Peter


Bodo Stroesser wrote:
> Peter wrote:
> 
>> I don't recall seeing an error where the obs and exp were equal.  I 
>> saw plenty where they were not equal.
>>
>> The code is pretty simple:
>> double observed = a[i];
>> double expected = (double) i;
>> if (observed != expected) {
>>           printf ("failed at i=%u, k=%u (obs %.18g vs exp %.18g)\n",i, 
>> k,observed, expected);
>> };
>>
>> Maybe it is just some unexpected handling on the != operator with 
>> doubles?
>>
>> Are you seeing cases where obs!=exp?  And difference if you run it on 
>> a uni-proc server vs. a smp server?
> 
> No. I just found a problem in SKAS sigcontext handling.
> The fp-registers are not restored correctly. Then, I remembered the 
> problems
> with memtest, which uses floatpoint.
> I modified the test to have sighandlers being started evey 10ms, using
> the fpu in the sighandler. Then, *many* error occured in my "memtest2".
> Without the modification, I couldn't reproduce the problems.
> 
> Two questions:
> 1) are you able to reproduce the problems in TT-mode?
> 2) do you have any idea, why a signal handler using floatpoint should be 
> started,
>    while running the original memtest?
> 
> Have attached my memtest2.c
> 
> Regards
> Bodo
> 
> P.S.: Mail with full description of the problem I've found will follow 
> soon.
> 
>>
>> Regards, Peter
>>
>> Bodo Stroesser wrote:
>>
>>> Carl wrote:
>>>
>>>> Hi,
>>>>
>>>> Running the piece of code from the URL below is generating errors on
>>>> various UML kernels:
>>>>
>>>> http://downloads.rimuhosting.com/memtest.c
>>>>
>>>> Kernels tested are: 2.4.27, 2.4.27-bs1, 2.6.9-bb4.
>>>>
>>>> Different UML host servers have been tried too, and only UMLs 
>>>> running on
>>>> SMP (dual Xeon) servers seem to have the problem (P4s with HT are 
>>>> fine).
>>>>
>>>> Can anyone else reproduce the errors? Any ideas?
>>>>
>>>> Thanks, Carl
>>
>>
>> Do you see messages like this one
>>
>>     "failed at i=17240, k=85 (obs 17240 vs exp 17240)"
>>
>> with obs and exp being equal?
> 
> 
> 
> ------------------------------------------------------------------------
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <signal.h>
> #include <sys/time.h>
> 
> #define N (20*1024)
> 
> void sighdlr(int sig)
> {
>     double a;
> 
>     a = 256;
> 
>     double observed = a;
>     double expected = 257;
> 
>     if ( observed == expected )
> 	printf("Error in sighdlr()\n");
> }
> 
> int
> main (void)
> {
>     size_t i, k;
>     struct itimerval itimer = { { 0, 10000}, { 0, 10000} };
> 
>     signal(SIGALRM, sighdlr);
>     setitimer( ITIMER_REAL, &itimer, NULL);
> 
>     for (k = 1; k < 1000; k++) {
> 	double *a = malloc (N * sizeof (double));
> 	if (a == 0) {
> 	    printf ("malloc failed at k=%u\n", k);
> 	    exit (1);
> 	}
> 
> 	for (i = 0; i < N; i++) {
> 	    a[i] = (double) i;
> 	    double observed = a[i];
> 	    double expected = (double) i;
> 	    if (observed != expected) {
> 		printf ("failed at i=%u, k=%u (obs %.18g vs exp %.18g)\n", i, k,
> 		        observed, expected);
> 	    }
> 	}
> 
> 	for (i = 0; i < N; i++) {
> 	    double observed = a[i];
> 	    double expected = (double) i;
> 	    if (observed != expected) {
> 		printf ("failed at i=%u, k=%u (obs %.18g vs exp %.18g)\n", i, k,
> 		        observed, expected);
> //		exit (1);
> 	    }
> 	}
> 	free (a);
>     }
>     exit (0);
> }


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