How do I set 64-bit alignment for gcc from the command line?

Question

In the man page I only found 8, 16 and 32 bits.

Answer 1

Use the -falign-* options: -falign-functions, -falign-labels, -falign-jumps.

Or, on i386/x86_64, if it's the stack boundary you want to keep aligned, use -mpreferred-stack-boundary=6 (2^6 = 64).