Checking for the Truncation of 64-bit Values

When you port to a 64-bit architecture such as V9, your data may be truncated. The truncation could happen implicitly, by assignment, at initialization, or by an explicit cast. The difference of two pointers is the typedef ptrdiff_t, which is a 32-bit integer type in 32-bit mode, and a 64-bit integer type in 64-bit mode. The truncation of a long to a smaller size integral type generates a warning as in the following example.

example% cat test1.c
int x[10];

int diff = &x[10] - &x[5]; //warn

example% CC -c -xarch=v9 -Qoption ccfe -xport64=full test1.c
"test1.c", line 3: Warning: Conversion of 64-bit type value to "int" causes truncation.
1 Warning(s) detected.
example%

Use -xport64=implicit to disable truncation warnings in 64bit compilation mode when an explicit cast is the cause of data truncation.

example% CC -c -xarch=v9 -Qoption ccfe -xport64=implicit test1.c
"test1.c", line 3: Warning: Conversion of 64-bit type value to "int" causes truncation.
1 Warning(s) detected.
example%

Another common issue that arises from porting to a 64-bit architecture is the truncation of a pointer. This is always an error in C++. An operation such as casting a pointer to an int which causes such a truncation results in an error diagnostic in V9 when you specify -xport64.

example% cat test2.c
char* p;
int main() {
  p =(char*) (((unsigned int)p) & 0xFF); // -xarch=v9 error
  return 0;
}
example% CC -c -xarch=v9 -Qoption ccfe -xport64=full test2.c
"test2.c", line 3: Error: Cannot cast from char* to unsigned.
1 Error(s) detected.
example%