Don't cast to void* and then to another type with a different alignment(DRAFT)

"It is undefined what will happen if a pointer of some type is converted to void*, and then the void* pointer is converted to a type with a stricter alignment requirement" -C99 rationaleV5.10.pdf

Non-compliant code example

char *char_ptr = "example";
int *int_ptr;

int *Function(void *v_pointer){
return pointer;
}
P2 = Function(pointer);

Pointer might be aligned on even boundary, once it is cast to an int some architectures will require it to be on 4 byte boundaries. Pointers are often cast because a void* cannot be dereferenced. Careless coding can result in an arbitrary pointer type being used irregardless of its alignment.

List of common alignments for Microsoft, Borland and GNU compilers to x86

char -1 byte aligned
short -2 byte aligned
int -4 byte aligned
float - 4 byte aligned
double - 8 byte on windows, 4 byte on linux

Compliant code suggestions

-make specific functions (avoid use of void*)

-always use strictest alignment type for arbitary pointers

Risk Assessment

Programs can crash

References

• Bryant, Randal and O'Hallaron, David. 2003 2001 Computer Systems: A Programmer's Perspective. Prentice Hall. ISBN 0-13-034074-X.
• http://www.open-std.org/jtc1/sc22/wg14/www/C99RationaleV5.10.pdf