Article: Q65818
Product(s): See article
Version(s): 6.00 | 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | s_quickc | mspl13_c
Last Modified: 24-OCT-1990
The following inline assembly code produces a NULL pointer assignment
when compiled with the compact or large memory models. The code should
store the ss:sp in the huge pointer tsrstack. However, the code
generated assumes that the variables will be in the segment referenced
by the DS register. This is not a correct assumption for a compact or
large memory model program. Thus, the values are moved into DGROUP
causing the R6001 NULL pointer assignment message.
This is NOT a compiler error. With inline assembly, the compiler makes
no changes to the code. Therefore, there is no segment override added
to the code to allow for tsrstack residing in another segment (in this
case FAR_DATA). It is the developer's responsibility to make sure that
the correct code is used for each memory model.
Sample Code
-----------
char _huge * tsrstack;
void main (void)
{
_asm MOV WORD PTR tsrstack[0], sp
_asm MOV WORD PTR tsrstack[2], ss
}
This program was extracted from the larger example program ALARM.C,
which is accessible through online help.