[Bug c/33720] New: A negative value in OpenMP clause num_threasds is not detected at runtime

[Bug c/33720] New: A negative value in OpenMP clause num_threasds is not detected at runtime

[geir at cray dot com]

The 'num_threads' clause in a OpenMP pragma is not being checked to see if it
is a positive integer.  An error should be return if it is not.

The OpenMP API Version 2.5 May 2005 on p. 28 lines 29-30 offers the following
restriction:

" * ... The num_threads expression must evaluate to a positive integer value."


$ cat bug2883.c
/* derived from ISU's RTED_OpenMP/C/Col3_Env_and_Claus_Errs/c_C_1_1_a.c test */
#include <omp.h>
#include <stdio.h>
#include <math.h>
int main() {
  double s, pi;
  int n_thread;
  int actual_num_threads;
  omp_set_num_threads(4);

  s = 0;
  pi = 4.0*atan(1.0);
  n_thread = (int) (sin(-0.25*pi)*10.0);

  printf("pi % 12.4f n_thread %d \n", pi, n_thread);
#pragma omp parallel default(none) shared(actual_num_threads)
num_threads(n_thread)
 {
#pragma omp single
   {
     actual_num_threads = omp_get_num_threads();
   }
 }

 printf("actual_num_threads = %d\n", actual_num_threads);
 return 0;
}

$ gcc -o x -fopenmp bug2883.c -lm
$ ./x 
pi       3.1416 n_thread -7

libgomp: Out of memory allocating 34359738400 bytes
$


-- 
           Summary: A negative value in OpenMP clause num_threasds is not
                    detected at runtime
           Product: gcc
           Version: 4.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: geir at cray dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

[Bug libgomp/33720] A negative value in OpenMP clause num_threasds is not detected at runtime

[bkoz at gcc dot gnu dot org]

------- Comment #1 from bkoz at gcc dot gnu dot org  2007-10-09 23:27 -------

I guess this is from:
http://rted.public.iastate.edu/OpenMP/homepage.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

[Bug libgomp/33720] A negative value in OpenMP clause num_threads is not detected at runtime

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2007-11-12 19:37 -------
I'm not sure we should do anything about this.
We have a warning if the compiler can detect non-positive value at compile
time,
but we certainly can't ever issue any diagnostic at runtime for num_threads
0 (because the implementation uses that value to mean no num_threads clause was
present) and I'm not convinced the runtime library needs to be verbose to
stderr.  So e.g. silently assuming just one thread is IMHO better than doing
gomp_fatal in there.  You shouldn't expect any particular behavior from program
which triggers undefined behavior.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

[Bug libgomp/33720] A negative value in OpenMP clause num_threads is not detected at runtime

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2008-08-07 02:55 -------
(In reply to comment #2)
> I'm not sure we should do anything about this.
> We have a warning if the compiler can detect non-positive value at compile
> time,
> but we certainly can't ever issue any diagnostic at runtime for num_threads
> 0 (because the implementation uses that value to mean no num_threads clause was
> present) and I'm not convinced the runtime library needs to be verbose to
> stderr.  So e.g. silently assuming just one thread is IMHO better than doing
> gomp_fatal in there.  You shouldn't expect any particular behavior from program
> which triggers undefined behavior.

But in this case the value is negative, not zero, and it seems that gomp_fatal
is already being called:

libgomp: Out of memory allocating 34359738400 bytes

It will be better to print the cause of that "out of memory" error, that is,
that the number of threads was negative.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org,
                   |                            |jakub at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

[Bug libgomp/33720] A negative value in OpenMP clause num_threads is not detected at runtime

[manu at gcc dot gnu dot org]

------- Comment #4 from manu at gcc dot gnu dot org  2009-07-31 15:11 -------
Geir, have you run the testcase with other compilers? What is the result?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

[Bug libgomp/33720] A negative value in OpenMP clause num_threads is not detected at runtime

[geir at cray dot com]

------- Comment #5 from geir at cray dot com  2009-09-14 19:59 -------
(In reply to comment #4)
> Geir, have you run the testcase with other compilers? What is the result?
> 

Changed test cast to use 2 threads ("omp_set_num_threads(2);")

  PGI 9.0-3

$ pgcc -mp bug2883.c
$ ./a.out
pi       3.1416 n_thread -7
Error: omp_set_num_threads value (-7) is invalid
$

  Pathscale 3.2.99:

$ pathcc -mp bug2883.c
$ ./a.out
pi       3.1416 n_thread -7
actual_num_threads = 1
$

  Intel/11.1.046:

$ icc -openmp bug2883.c
$ ./a.out
pi       3.1416 n_thread -7
actual_num_threads = 2
$

  Cray 7.1.3:

$ cc -target=native bug2883.c
$ ./a.out
pi       3.1416 n_thread -7
actual_num_threads = 2
$

$


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

[Bug libgomp/33720] A negative value in OpenMP clause num_threads is not detected at runtime

[geir at cray dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

--- Comment #6 from Geir Johansen <geir at cray dot com> ---
Fails in GCC 4.8.0:

$ gcc --version
gcc (GCC) 4.8.0 20130322 (Cray Inc.)
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gcc -o x -fopenmp bug2883.c -lm
$ ./x
pi       3.1416 n_thread -7

libgomp: Out of memory allocating 481036337712 bytes
$

[Bug libgomp/33720] A negative value in OpenMP clause num_threads is not detected at runtime

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I still believe it is not needed to slow down the runtime library with checks
for invalid programs.  Negative num_threads is undefined behavior, just don't
do it.

[Bug libgomp/33720] A negative value in OpenMP clause num_threads is not detected at runtime

[manu at gcc dot gnu.org]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="UTF-8", Size: 4302 bytes --]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

--- Comment #8 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #7)
> I still believe it is not needed to slow down the runtime library with
> checks for invalid programs.  Negative num_threads is undefined behavior,
> just don't do it.

Perhaps the check could be added with the new -fsanitize=undefined?
>From gcc-bugs-return-424664-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Wed Jun 19 20:46:09 2013
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From: "zsojka at seznam dot cz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/57655] New: [4.8/4.9 Regression] ICE: in create_pre_exit, at mode-switching.c:418 with -mno-fp-ret-in-387 -mvzeroupper -mxop and __builtin_ilogbl()
Date: Wed, 19 Jun 2013 20:46:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idW655

            Bug ID: 57655
           Summary: [4.8/4.9 Regression] ICE: in create_pre_exit, at
                    mode-switching.c:418 with -mno-fp-ret-in-387
                    -mvzeroupper -mxop and __builtin_ilogbl()
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz

Created attachment 30324
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id0324&actioníit
reduced testcase

Compiler output:
$ gcc -mno-fp-ret-in-387 -mvzeroupper -mxop testcase.c
testcase.c: In function 'foo':
testcase.c:5:1: internal compiler error: in create_pre_exit, at
mode-switching.c:418
 }
 ^
0x1178ceb create_pre_exit
        /mnt/svn/gcc-trunk/gcc/mode-switching.c:404
0x1178ceb optimize_mode_switching
        /mnt/svn/gcc-trunk/gcc/mode-switching.c:493
0x1178ceb rest_of_handle_mode_switching
        /mnt/svn/gcc-trunk/gcc/mode-switching.c:779
0xc97d17 rest_of_handle_insert_vzeroupper
        /mnt/svn/gcc-trunk/gcc/config/i386/i386.c:2599
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.

$ gcc -v
Using built-in specs.
COLLECT_GCC=/mnt/svn/gcc-trunk/binary-latest/bin/gcc
COLLECT_LTO_WRAPPER=/mnt/svn/gcc-trunk/binary-200176-lto-fortran-checking-yes-rtl-df/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /mnt/svn/gcc-trunk//configure --enable-checking=yes,rtl,df
--enable-languages=c,c++,lto,fortran
--prefix=/mnt/svn/gcc-trunk/binary-200176-lto-fortran-checking-yes-rtl-df/
--without-cloog --without-ppl
Thread model: posix
gcc version 4.9.0 20130618 (experimental) (GCC)

Tested revisions:
r200211 - ICE
4.8 r198018 - ICE
4.7 r198018 - OK

[Bug libgomp/33720] A negative value in OpenMP clause num_threads is not detected at runtime

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=33720

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-12-29

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.