I'm in the process of writing a memory allocator for a project of mine; needless to say, GCC is one of the targeted compilers. I find myself having to think about what memory alignment rules to guarantee for pointers returned from my allocator. I know that some subset of instructions on some architectures work much faster when operating on properly aligned data. Furthermore, I know that other such instructions flat out fail to work if operating on improperly aligned data. The question is: does GCC use such instructions? I don't want to return poorly aligned data from my alloc() function and have GCC try to use an aligned-only instruction it, resulting in things exploding at runtime. __alignof__ seems like it might be of some help: http://gcc.gnu.org/onlinedocs/gcc-4.3.3/gcc/Alignment.html#Alignment But unfortunately it doesn't tell me what the _strictest_ alignment rule is, which is what I need to know to write a generic memory allocator. Does GCC document or otherwise make known what minimum alignment it expects on each platform? I wish I could detect this automatically at build time; or during ./configure time (it's an autotools projects). Thanks for reading, -Patrick
