Q43319: C: exec and spawn (P_OVERLAY) Will Fail When Bound

Article: Q43319
Product(s): See article
Version(s): 5.10   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | O_OS2SDK | mspl13_c
Last Modified: 15-JAN-1990

The Microsoft C run-time library functions exec and spawn (with a
P_OVERLAY attribute) do not work correctly when executed in a bound
application under DOS. This is briefly documented on Page 24 of the
"Microsoft C for MS OS/2 and MS-DOS Operating Systems: Version 5.1
Update" manual. The execution will fail with the program returning the
following error message:

   run-time error R6006
   - bad format on exec

This occurs only when the dual-mode program is running under DOS. A
spawn with the P_WAIT attribute will work properly.

Examining the DosExecPgm() API reveals that there is no option to
overlay the currently executing program. OS/2's protection scheme does
not support overwriting the code segment; therefore, to exec another
program, it is necessary to actually spawn the program in a different
area of memory and terminate the current process.

To create a bound program that uses overlays, not only would a
remapping of the FAPI function be necessary, but also a complete
reprogramming to allow for loading over the current code segment. At
this time, BIND does not support this.

The following functions do not work properly when executed under DOS
in a bound application:

   execl    execle  execlp   execlpe   execv    execve   execvp
   execvpe  spawnl  spawnl   spawnle   spawnlp  spawnlpe spawnv
   spawnve  spawnvp spawnvpe

Note: The spawn functions fail only with the P_OVERLAY attribute.

The following program will fail to spawn PROG.EXE from DOS:

/* Program:  spawn.c                                      */
/*                                                        */
/* Compile and bind from OS/2 with:                       */
/*                                                        */
/*         cl /Lp spawn.c                                 */
/*         bind spawn /c/lib/api.lib /c/lib/doscalls.lib  */

#include <stdio.h>
#include <process.h>

void main(void)
{
  spawnl(P_OVERLAY,"c:\\tmp\\prog.exe","prog",NULL);
}

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.