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Mail Archives: djgpp/1997/11/17/14:21:48

Date: Mon, 17 Nov 1997 20:20:28 +0100 (GMT)
From: "X DOT PONS AT UAB DOT ES" <ILGES AT cc DOT uab DOT es>
Subject: system calls generate Segm.Viol. on NT
To: djgpp AT delorie DOT com
Message-id: <01IQ4NN88GG200LLZ6@cc.uab.es>
Organization: Universitat Autonoma de Barcelona
MIME-version: 1.0

Dear programmers,

This code perfectly runs on DOS, Windows 3.1x DOS-box and
Windows 95 DOS-box, but it crashes on a NT 4.0 (NTFS). It simply
runs a "dir c:\\" command froma a system() call and stores the
output to a file in the c: root.

=== START OF CODE ===
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
FILE *pf;
int c;

	if (system("dir c:\\ > c:\\somefile.txt"))
	  { printf("\n\asystem() error"); return 1; }

   if ((pf=fopen("c:\\somefile.txt", "rt"))==NULL)
     { puts ("\n\aCannot open file..."); return 1; }

   while ((c=getc(pf))!=EOF)
	   putchar(c);

   fclose(pf);

	return 0;
}
=== END OF CODE ===
If the command line is "dir c:\\" instead of "dir c:\\ > c:\\somefile.txt"
it also crashes, so the redirector '>' does not seem the responsible.
On the other hand, putting this line on a BAT and running it from a
system also crashes.

More details:

  1/ Sometimes it does not crash the first time it is executed,
     but if you simply rerun the program, it crashes every time
     until the DOS box is closed.

  2/ When this code is compiled in BC 3.x (16-bit) or in
     Borland C++ 5.02 (32-bit WIN32 application), it runs
     perfectly and does not produce any change in the free
     memory.

  3/ The symify help for the output is as follows.

      Exiting due to signal SIGSEGV
      General Protection Fault at eip=00003b94
      eax=fff40000 ebx=00000000 ecx=000001f9 edx=fff40000 esi=00004000 edi=0000000b
      ebp=00053070 esp=00053060 cs=01cf ds=01d7 es=01d7 fs=019f gs=01df ss=01d7
      Call frame traceback EIPs:
        0x00003b94   _malloc+308
        0x00003b11   _malloc+177
        0x000079b7   __flsbuf+159
        0x00002a4d   _putchar+25
        0x000015fc   _main+108
        0x00001b47   ___crt1_startup+115

  4/ The "mem /c" command reports that 16 bytes have been loosed after
     a DJ program runs on our NT console (but NOT on other O.S.), but
     it happens on any program, even the "Hello world".

     ** Normal situation: ********

      Memoria convencional :

        Nombre             Tamano en decimal      Tamano en Hex
      -------------      ---------------------   -------------
        MSDOS              11344      ( 11.1K)         2C50
        KBD                 3280      (  3.2K)          CD0
        HIMEM               1248      (  1.2K)          4E0
        COMMAND             3440      (  3.4K)          D70
        KB16                6096      (  6.0K)         17D0
        FREE                 112      (  0.1K)           70
        FREE                 544      (  0.5K)          220
        FREE              629088      (614.3K)        99960

      Total libre :       629744      (615.0K)

      Memoria superior :

        Nombre             Tamano en decimal      Tamano en Hex
      -------------      ---------------------   -------------
        SYSTEM            163824      (160.0K)        27FF0
        MOUSE              12528      ( 12.2K)         30F0
        MSCDEXNT             464      (  0.5K)          1D0
        REDIR               2672      (  2.6K)          A70
        DOSX               38864      ( 38.0K)         97D0
 >> !   FREE                 544      (  0.5K)          220
        FREE              108640      (106.1K)        1A860

      Total libre :       109184      (106.6K)

      Bytes disponibles para programas (Convencional+Sup.):     738928   (721.6K)
      Tamano del mayor programa:                                629088   (614.3K)
      Mayor bloque de memoria superior disponible:              108640   (106.1K)

         1048576 bytes totales de memoria extendida contigua
               0 bytes disponibles de memoria extendida contigua
          931840 bytes de memoria XMS disponible
                 MS-DOS est  residente en HMA

     ** After "Hello world" execution: ********

      Memoria convencional :

        Nombre             Tamano en decimal      Tamano en Hex
      -------------      ---------------------   -------------
        MSDOS              11344      ( 11.1K)         2C50
        KBD                 3280      (  3.2K)          CD0
        HIMEM               1248      (  1.2K)          4E0
        COMMAND             3440      (  3.4K)          D70
        KB16                6096      (  6.0K)         17D0
        FREE                 112      (  0.1K)           70
        FREE                 544      (  0.5K)          220
        FREE              629088      (614.3K)        99960

      Total libre :       629744      (615.0K)

      Memoria superior :

        Nombre             Tamano en decimal      Tamano en Hex
      -------------      ---------------------   -------------
        SYSTEM            163824      (160.0K)        27FF0
        MOUSE              12528      ( 12.2K)         30F0
        MSCDEXNT             464      (  0.5K)          1D0
        REDIR               2672      (  2.6K)          A70
        DOSX               38864      ( 38.0K)         97D0
 >> !   FREE                  48      (  0.0K)           30
 >> !   FREE                 480      (  0.5K)          1E0
        FREE              108640      (106.1K)        1A860

      Total libre :       109168      (106.6K)

      Bytes disponibles para programas (Convencional+Sup.):     738912   (721.6K)
      Tamano del mayor programa:                                629088   (614.3K)
      Mayor bloque de memoria superior disponible:              108640   (106.1K)

         1048576 bytes totales de memoria extendida contigua
               0 bytes disponibles de memoria extendida contigua
          931840 bytes de memoria XMS disponible
                 MS-DOS est  residente en HMA


     Note that the first FREE block has been broken in two
     pieces but they lack 16 bytes. Sorry if this is not
     relevant, it is only a symptom thas is strange for
     us (running DJ applications on DOS, Windows 3 or 95
     leaves the memory in the same "distribution").


Any idea on how to run other programs or internal commands from
a DJGPP program? We have already tried:
  - system("command /C dir c:\\ > somefile.txt");
  - to put the "dir c:\\ > somefile.txt" string on a file.BAT
    and then call system(file.BAT);
  - spawnl(P_WAIT) instead of system().
  - system("start /W command /C dir c:\\ > somefile.txt");
without success. :-((((


Thanks for any help!

Joan Maso and Xavier Pons


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