On Mon, Oct 12, 2015 at 11:11 AM, Abhishek Aggarwal <abhiinnit...@gmail.com> wrote: > I was befuddled by the following 3 assembly instructions (generated > right in the beginning of 'main' function): > lea 0x4(%esp), %ecx > and 0xfffffff0, %esp > pushl -0x4(%ecx) > > I am not able to understand the purpose of these 3 instructions. Can > anyone explain me about them? I didn't observe these 3 instructions > when I compiled the same code with '-m64' switch instead of '-m32'.
This is for aligning the stack to 16 bytes. IIRC, the x86 ABI on Linux does not mandate a stack alignment greater than 4 bytes (or 8 -- not sure about the exact number), whereas the one for x86_64 does.
