C++ :: Data Alignment Across Different Platforms

Basically, I'm working on a code that has its own allocator class. In the backend, the class uses malloc() to create huge blocks of memory aligned to sizeof(void*).

Apparently, in certain special circumstances, sizeof(void*) will be 4 when the data actually needs to be aligned to 8 bytes. If the memory isn't aligned to 8 bytes, there will be heap corruption and a bus error will occur. One such case is on HP-UX; we forced the alignment to 8 bytes on that platform. According to the commit log, HP-UX has a minimum struct size of 8 bytes and that's why it has to be aligned to 8 bytes (but I can't confirm if this is actually true).

We're running into these same problems when compiling on MIPS, MIPSel, and SPARC (all 32-bit builds).

(Side thought just now as I wrote that: seems like RISC processors don't allow unaligned access while x86 processors do. It looks like these build failures on MIPS and SPARC were while trying to build 32-bit on 64-bit hardware, could this be the problem?)

Anyway, the ultimate question and goal here is to find out how to detect this magical minimum alignment size, if not sizeof(void*).