This affects code where multiple structs or unions are assigned by successive = operators in one expression, e.g. "s1=s2=s3". The middle struct assignment(s) would use the ~Move2 or ~LongMove2 helper functions (for <64k or >=64k moves, respectively). These functions are supposed to leave the destination pointer on the stack so it can be used as the source of a subsequent move, but they both had bugs where they could modify dest and leave that modified value on the stack, which would cause subsequent moves to use the wrong source location. In the case of ~Move2, this only happened if the size was odd.
Here is a program that demonstrated the problems with both functions:
#pragma memorymodel 1
#include <stdio.h>
struct S1 {
char s[80000];
} a,b,c;
int main(void) {
struct S2 {
int x,y;
char z;
} d,e,f;
c.s[66000] = 123;
f.y = 5678;
a = b = c;
d = e = f;
printf("%i %i %i\n", a.s[66000], b.s[66000], c.s[66000]);
printf("%i %i %i\n", d.y, e.y, f.y);
}
Stephen Heumann
Kelvin Sherlock
mikew50