According to the Wikipedia page Segmentation fault, a bus error can be caused by unaligned memory access. The article gives an example about how to trigger a bus error. In the example, we have to enable alignment checking to see the bus error. What if we disable such alignment checking?
The program seems to work properly. I have a program access unaligned memory frequently, and it is used by quite a few people, but no one reports bus errors or other weird results to me. If we disable alignment checking, what is the side effect of unaligned memory?
Platforms: I am working on x86/x86-64. I also tried my program by compiling it with “gcc -arch ppc” on a Mac and it works properly.
It may be significantly slower to access unaligned memory (as in, several times slower).
Not all platforms even support unaligned access – x86 and x64 do, but ia64 (Itanium) does not, for example.
A compiler can emulate unaligned access (VC++ does that for pointers declared as
__unalignedon ia64, for example) – by inserting additional checks to detect the unaligned case, and loading/storing parts of the object that straddle the alignment boundary separately. That is even slower than unaligned access on platforms which natively support it, however.