On Tue, Aug 11, 2009 at 11:55 PM, Pavel Roskinproski@gnu.org wrote:
Hello!
The reason OpenBIOS violates the strict aliasing rules so often is because it uses char arrays to represent endian-specific data.
Char arrays may have alignment different from that of the longer types. That's why casting a pointer to such array to a pointer to a longer type and dereferencing it is considered unsafe by the compiler. The compiler assumes that different types would not occupy the same memory unless we tell it not to make such assumption.
Char arrays serve as protection against misusing endian-specific data as host-endian integers. The alternative it to use sparse annotated types, such as __le32. __le32 has the same alignment as u32, but sparse would recognize attempts to use __le32 in arithmetic operations.
I think switching to sparse annotated types would be a good idea whether strict aliasing is disabled or not. It makes the code more readable. It could also fix some hard to find bugs.
Would it be possible and/or useful to use sparse types for cell types?