From:"The GCC devs decided to unilaterally change the Linux x86 ABI [1] [2] [3] [4]. I'm not sure when this happened, but I think it first became a common problem with GCC 4.1. Previously the Linux x86 ABI was the "SysV i386 ABI", which stated that the stack is aligned to a 4-byte boundary on function entry. GCC now assumes by default that the stack is aligned to a 16-byte boundary. This is an very controversial issue with the GCC devs saying they have changed the ABI, and many other people considering the SysV ABI to be the real ABI and GCC to be buggy. GCC Bugzilla is full of flamewars. GCC devs have said "GCC chose to change the unwritten standard for the ABI in use for IA32 GNU/Linux" and "The ABI is undocumented; that is reality" [3]"