Segmentation Fault

[Christian Lande]

Hi all,

can anybody help me with the following code:

#include <stdio.h>
#include <emmintrin.h>
#define M 2
int main () {
int i;
__m128d *s, ts, td;

double *p = malloc(M*sizeof (*p)); //A
// double p[2]; //B

if (p==NULL) return 0;

p[0]=p[1]=1.0;

printf("%.3f %.3f\n", p[0], p[1]);

s = (__m128d *)p; //D
if (s != p) return 0;
ts = *s;
td = _mm_add_pd(ts, ts);
*s = td; //C

printf("%.3f %.3f\n", p[0], p[1]);
}

Line "C" causes a Segmentation Fault and I don't know why. If I replace line
"A" with line "B" it works correctly. Something must be wrong with line "D"
maybe somebody knows what?

Thanks for any help,
ChL

PS: I'm using an Intel Compiler icc version 8.0 on a Xeon machine compiling
with the command "icc test.c -o test -march=pentium4" .

[Mark A. Odell]

Re: Segmentation Fault

"Christian Lande" <IIZUXMKQOEHH@s pammotel.com> wrote in
news:cb9lot$fn2 $04$1@news.t-online.com:
[color=blue]
> Hi all,
>
> can anybody help me with the following code:
>
> #include <stdio.h>
> #include <emmintrin.h>
> #define M 2
> int main () {
> int i;
> __m128d *s, ts, td;
>
> double *p = malloc(M*sizeof (*p)); //A
> // double p[2]; //B
>
> if (p==NULL) return 0;
>
> p[0]=p[1]=1.0;
>
> printf("%.3f %.3f\n", p[0], p[1]);
>
> s = (__m128d *)p; //D[/color]

What the heck is __m128d? Hint: it's not ISO C so how can we help you
here?


--
- Mark ->
--

[Christian Lande]

Re: Segmentation Fault

"Mark A. Odell" <odellmark@hotm ail.com> wrote:
[color=blue]
> What the heck is __m128d? Hint: it's not ISO C so how can we help you
> here?[/color]

yes, you are right, it's not ISO C, sorry. But I don't know any other
position where to ask such a question and I'm sure here are some people who
know the answer.

If you are interested in what is __m128d, you can look here
http://msdn.microsoft.com/library/de...lrf__m128d.asp
e.g. Some other compilers (like Intel icc for linux and windows) implement
it in the same way.

Thx for your answer,
ChL

[Darrell Grainger]

Re: Segmentation Fault

On Tue, 22 Jun 2004, Christian Lande wrote:
[color=blue]
> Hi all,
>
> can anybody help me with the following code:
>
> #include <stdio.h>
> #include <emmintrin.h>[/color]

Have no idea what this header is. Without an explanation this could have
some impact.
[color=blue]
> #define M 2
> int main () {
> int i;
> __m128d *s, ts, td;[/color]

What is __m128d? This is not a standard data type.
[color=blue]
> double *p = malloc(M*sizeof (*p)); //A[/color]

First use of malloc without prototype. You need to add an #include
<stdlib.h> to your program.
[color=blue]
> // double p[2]; //B
>
> if (p==NULL) return 0;
>
> p[0]=p[1]=1.0;
>
> printf("%.3f %.3f\n", p[0], p[1]);
>
> s = (__m128d *)p; //D[/color]

Here I still have no idea what __m128d is and how it will affect things.
[color=blue]
> if (s != p) return 0;[/color]

This tells me that the implicit conversion and explicit conversion must be
the same to get passed this point. Is sizeof *p == sizeof *s? If not then
what is going on here?
[color=blue]
> ts = *s;
> td = _mm_add_pd(ts, ts);
> *s = td; //C[/color]

Is this definitely C? The use of C++ style comments makes me wonder. If it
is C, sizeof *p < sizeof *s could cause a crash here. Or are you assuming
that sizeof p[0] + sizeof p[1] == sizeof *s?

If that is the case, why not use a union that contains pointers to
doubles and a pointer to a __m128d. It would be more clear and the
compiler might catch something you are missing.
[color=blue]
> printf("%.3f %.3f\n", p[0], p[1]);[/color]

P.S. if main returns an int, where is your return statement?
[color=blue]
> }
>
> Line "C" causes a Segmentation Fault and I don't know why. If I replace line
> "A" with line "B" it works correctly. Something must be wrong with line "D"
> maybe somebody knows what?
>
> Thanks for any help,
> ChL
>
> PS: I'm using an Intel Compiler icc version 8.0 on a Xeon machine compiling
> with the command "icc test.c -o test -march=pentium4" .
>
>
>[/color]

--
Send e-mail to: darrell at cs dot toronto dot edu
Don't send e-mail to vice.president@ whitehouse.gov

[Irrwahn Grausewitz]

Re: Segmentation Fault

"Christian Lande" <IIZUXMKQOEHH@s pammotel.com> wrote:[color=blue]
>Hi all,
>
>can anybody help me with the following code:
>
>#include <stdio.h>
>#include <emmintrin.h>[/color]

As Mark already pointed out, by including this header you left
the realm of portable standard C.
[color=blue]
>#define M 2
>int main () {
> int i;
> __m128d *s, ts, td;
>
> double *p = malloc(M*sizeof (*p)); //A[/color]

You forgot to #include <stdlib.h> before calling malloc; this might
well be the reason for the problem.
[color=blue]
>// double p[2]; //B
>
> if (p==NULL) return 0;
>
> p[0]=p[1]=1.0;
>
> printf("%.3f %.3f\n", p[0], p[1]);
>
> s = (__m128d *)p; //D
> if (s != p) return 0;
> ts = *s;
> td = _mm_add_pd(ts, ts);
> *s = td; //C
>
> printf("%.3f %.3f\n", p[0], p[1]);
>}
>
>Line "C" causes a Segmentation Fault and I don't know why.[/color]

If including stdlib.h didn't fix the code, here's another possible
cause for the segfault: if an object of type __m128d (whatever that
is) requires more memory than p points to, you write to memory your
program doesn't own in line "C".

<snip>

Regards
--
Irrwahn Grausewitz (irrwahn33@free net.de)
welcome to clc: http://www.ungerhu.com/jxh/clc.welcome.txt
clc faq-list : http://www.faqs.org/faqs/C-faq/faq/
clc OT guide : http://benpfaff.org/writings/clc/off-topic.html

[Dan Pop]

Re: Segmentation Fault

In <cb9lot$fn2$04$ 1@news.t-online.com> "Christian Lande" <IIZUXMKQOEHH@s pammotel.com> writes:
[color=blue]
>#include <stdio.h>
>#include <emmintrin.h>[/color]

???
[color=blue]
>#define M 2
>int main () {
> int i;
> __m128d *s, ts, td;[/color]

I assume __m128d is an 128-bit (16 byte) type.
[color=blue]
> double *p = malloc(M*sizeof (*p)); //A
>// double p[2]; //B
>
> if (p==NULL) return 0;
>
> p[0]=p[1]=1.0;
>
> printf("%.3f %.3f\n", p[0], p[1]);
>
> s = (__m128d *)p; //D
> if (s != p) return 0;[/color]
^^^^^^
Is the compiler silently accepting this line? It doesn't look like
__m128d is merely an alias for double and you can't compare pointers to
different types.
[color=blue]
> ts = *s;[/color]

If this works, then //C should, in principle, work, too.
[color=blue]
> td = _mm_add_pd(ts, ts);
> *s = td; //C[/color]

The only explanation for a failure here after the success of "ts = *s;"
is that the _mm_add_pd(ts, ts) call invoked undefined behaviour.
[color=blue]
> printf("%.3f %.3f\n", p[0], p[1]);
>}
>
>Line "C" causes a Segmentation Fault and I don't know why. If I replace line
>"A" with line "B" it works correctly.[/color]

This replacement generates a different stack layout, so it may be a red
herring.
[color=blue]
>Something must be wrong with line "D" maybe somebody knows what?[/color]

In this case, "ts = *s;" should have generated the crash. But this
didn't happen, so the pointer value is OK.
[color=blue]
>Thanks for any help,
>ChL
>
>PS: I'm using an Intel Compiler icc version 8.0 on a Xeon machine compiling
>with the command "icc test.c -o test -march=pentium4" .[/color]

Your code is not standard C code and your problem has nothing to do
with standard C.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Dan.Pop@ifh.de

[Christian Lande]

Re: Segmentation Fault

Ok, thanks to all of you for reading and trying to help, meanwhile I solved
the problem.

It was because of the fact, that this __m128d-type was defined with an
alignment of every 16 Bytes, so I got the problem because of my reserved
double field has an alignment of every 8 Bytes.

Because of your comments that this is not the right group, can you give me a
hint where to ask for such things, please? These problems occouring from
time to time and I've allways the same problem not knowing where to ask for.

Thx,
ChL

[Dan Pop]

Re: Segmentation Fault

In <c7sgd0tr6oensk 7lnnfn5mrfj6es2 fnd6t@4ax.com> Irrwahn Grausewitz <irrwahn33@free net.de> writes:
[color=blue]
>"Christian Lande" <IIZUXMKQOEHH@s pammotel.com> wrote:[color=green]
>>Hi all,
>>
>>can anybody help me with the following code:
>>
>>#include <stdio.h>
>>#include <emmintrin.h>[/color]
>
>As Mark already pointed out, by including this header you left
>the realm of portable standard C.
>[color=green]
>>#define M 2
>>int main () {
>> int i;
>> __m128d *s, ts, td;
>>
>> double *p = malloc(M*sizeof (*p)); //A[/color]
>
>You forgot to #include <stdlib.h> before calling malloc; this might
>well be the reason for the problem.[/color]

If he did, indeed, the compiler should have complained: a diagnostic is
required.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Dan.Pop@ifh.de

[CBFalconer]

Re: Segmentation Fault

Christian Lande wrote:[color=blue]
>
> can anybody help me with the following code:
>
> #include <stdio.h>
> #include <emmintrin.h>[/color]

unknown header.
[color=blue]
> #define M 2
> int main () {[/color]

int main (void) is better
[color=blue]
> int i;
> __m128d *s, ts, td;[/color]

illegal identifier __m128d. Reserved for implementation
[color=blue]
>
> double *p = malloc(M*sizeof (*p)); //A
> // double p[2]; //B[/color]

// comments are ill advised in newsgroups, require C99 compiler.
You probably don't have one. Use /* ... */ instead.
[color=blue]
>
> if (p==NULL) return 0;
>
> p[0]=p[1]=1.0;
>
> printf("%.3f %.3f\n", p[0], p[1]);
>
> s = (__m128d *)p; //D[/color]

Again, unideclared and illegal identifier. Bad comment.
[color=blue]
> if (s != p) return 0;[/color]

Why should it be? They point to different types.
[color=blue]
> ts = *s;[/color]

ts is of type blah, s of type pointer to blah (I won't sink to
typing __m128d). Even more things must be undefined by now.
[color=blue]
> td = _mm_add_pd(ts, ts);[/color]

Another illegal identifier, also undefined.
[color=blue]
> *s = td; //C
>
> printf("%.3f %.3f\n", p[0], p[1]);
> }
>
> Line "C" causes a Segmentation Fault and I don't know why. If I
> replace line "A" with line "B" it works correctly. Something must
> be wrong with line "D" maybe somebody knows what?
>
> Thanks for any help,
> ChL
>
> PS: I'm using an Intel Compiler icc version 8.0 on a Xeon machine
> compiling with the command "icc test.c -o test -march=pentium4" .[/color]

If that matters you are off topic.

--
Chuck F (cbfalconer@yah oo.com) (cbfalconer@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!

[CBFalconer]

Re: Segmentation Fault

Christian Lande wrote:[color=blue]
>[/color]
.... snip ...[color=blue]
>
> Because of your comments that this is not the right group, can
> you give me a hint where to ask for such things, please? These
> problems occouring from time to time and I've allways the same
> problem not knowing where to ask for.[/color]

Your best bet is to stick to pure ISO standard portable C and
eschew system specific extensions. The end convenience will pay
for itself many times over.

If this is not possible you should, in this case, look for a
newsgroup with 'Microsoft' in its name. In that case you should
also isolate your non-portable code to a file or two.

--
Chuck F (cbfalconer@yah oo.com) (cbfalconer@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!

[Barry Schwarz]

Re: Segmentation Fault

On Tue, 22 Jun 2004 18:13:00 +0200, "Christian Lande"
<IIZUXMKQOEHH@s pammotel.com> wrote:
[color=blue]
>Hi all,
>
>can anybody help me with the following code:
>
>#include <stdio.h>
>#include <emmintrin.h>
>#define M 2
>int main () {
> int i;
> __m128d *s, ts, td;
>
> double *p = malloc(M*sizeof (*p)); //A
>// double p[2]; //B
>
> if (p==NULL) return 0;
>
> p[0]=p[1]=1.0;
>
> printf("%.3f %.3f\n", p[0], p[1]);
>
> s = (__m128d *)p; //D
> if (s != p) return 0;[/color]

Doesn't your compiler generate a diagnostic for this? The two pointer
types are incompatible unless __m128d is just a typedef for double.
[color=blue]
> ts = *s;
> td = _mm_add_pd(ts, ts);
> *s = td; //C[/color]

What is the sizeof(__m128d) ? If it is larger than 2*sizeof(double )
you are attempting to write to memory you don't own.
[color=blue]
>
> printf("%.3f %.3f\n", p[0], p[1]);
>}
>
>Line "C" causes a Segmentation Fault and I don't know why. If I replace line
>"A" with line "B" it works correctly. Something must be wrong with line "D"[/color]

If it is the size problem mentioned above, line C will overwrite other
variables in your program but at least you own that memory.

However, both overwrites invoke undefined behavior so it really won't
work even if it appears to.
[color=blue]
>maybe somebody knows what?[/color]

With line A, line D cannot be the problem because the value returned
from malloc is guaranteed to be properly aligned for any type,
including __m128d. With line B, we don't know if p will be properly
aligned.

If you really want help, you are going to have to give us all the
non-standard details. What is type __m128d? What does _mm_add_pd do?


<<Remove the del for email>>

[Ulrich Eckhardt]

Re: Segmentation Fault

Christian Lande wrote:[color=blue]
> #include <emmintrin.h>
> #define M 2
> __m128d *s, ts, td;
>
> double *p = malloc(M*sizeof (*p)); //A
> // double p[2]; //B
>
> if (p==NULL) return 0;
>
> p[0]=p[1]=1.0;
>
> printf("%.3f %.3f\n", p[0], p[1]);
>
> s = (__m128d *)p; //D
> if (s != p) return 0;
> ts = *s;
> td = _mm_add_pd(ts, ts);
> *s = td; //C
>
> printf("%.3f %.3f\n", p[0], p[1]);
> }
>
> Line "C" causes a Segmentation Fault and I don't know why.
> If I replace line "A" with line "B" it works correctly.
> Something must be wrong with line "D" maybe somebody knows what?[/color]

Casts are always wrong, only that they sometimes are the only cure. Here
however, you say that it should interpret the address 'p' as a '__m128d*'.
'd' only holds so much storage, so why don't you first make sure that
there is enough?

$include <assert.h>
assert( (sizeof *s) <= (M * (sizeof *p)));

The fact that it does seem to work with 'B' activated is just luck. Try
adding another var after p, and output its value before and after 'C'. The
stack area was already allocated to your process, but that doesn't mean
you are allowed to use it. The heap is allocated more exactly to fit your
needs, crossing these bounds therefore earlier causes the segmentation
fault.

Oh, while you are at it, could you please remove everything that is not
necessary to demonstrate your problem, e.g. the call to _mm_add_pd()?

Uli

--
FAQ: http://ma.rtij.nl/acllc-c++.FAQ.html

[Ulrich Eckhardt]

Re: Segmentation Fault

Darrell Grainger wrote:[color=blue]
> On Tue, 22 Jun 2004, Christian Lande wrote:[color=green]
>> *s = td; //C[/color]
>
> Is this definitely C? The use of C++ style comments makes me wonder.[/color]

C allows those comments. It didn't always allow them, but it does now (and
many compilers have been accepting it for some time).

Uli

[Ravi Uday]

Re: Segmentation Fault

Comments inline..

"Christian Lande" <IIZUXMKQOEHH@s pammotel.com> wrote in message news:<cb9lot$fn 2$04$1@news.t-online.com>...[color=blue]
> Hi all,
>
> can anybody help me with the following code:
>
> #include <stdio.h>
> #include <emmintrin.h>[/color]

Never heard of this header. System specific headers are not discussed
here..
[color=blue]
> #define M 2
> int main () {
> int i;
> __m128d *s, ts, td;[/color]

/* whats this __m128d ... its not a C datatype that i've known. */[color=blue]
>
> double *p = malloc(M*sizeof (*p)); //A
> // double p[2]; //B
>
> if (p==NULL) return 0;
>
> p[0]=p[1]=1.0;
>
> printf("%.3f %.3f\n", p[0], p[1]);
>
> s = (__m128d *)p; //D[/color]

/* Unless you tell us whats __m128d stands for how can we know
whats happ ?*/
[color=blue]
> if (s != p) return 0;
> ts = *s;
> td = _mm_add_pd(ts, ts);[/color]

/* mm_add_pd.. where is this defined ! I think its in this function
the culprit is, there is some inconsistency in the params you have
passed. Did you make a typo !!!! */[color=blue]
> *s = td; //C
>
> printf("%.3f %.3f\n", p[0], p[1]);
> }[/color]

Since main is declared as function that returns 'int' before exiting
the function, call return with 0/EXIT_FAILURE..e tc..
[color=blue]
>
> Line "C" causes a Segmentation Fault and I don't know why. If I replace line
> "A" with line "B" it works correctly. Something must be wrong with line "D"
> maybe somebody knows what?
>
> Thanks for any help,
> ChL
>[/color]

Its better you post here a compilable code for us to run/exec and test
your program. By this we can make our statements/suggestions clear and
crisp.

[Christian Lande]

Re: Segmentation Fault

"CBFalconer " <cbfalconer@yah oo.com> wrote:
[color=blue]
> If this is not possible you should, in this case, look for a
> newsgroup with 'Microsoft' in its name.[/color]

I don't understand this suggestion. What should the code in a
'Microsoft'-Group, it was coded for a Xeon with Red Hat Linux?
[color=blue]
> In that case you should
> also isolate your non-portable code to a file or two.[/color]

For what reason? In most groups attachments are not not gladly seen.

Thx for your answer,
ChL