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

[Bodo Stroesser <bstroesser@fujitsu-siemens.com>]

[-- Attachment #1: Type: text/plain, Size: 1888 bytes --]

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?


[-- Attachment #2: memtest2.c --]
[-- Type: text/plain, Size: 1138 bytes --]

#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);
}