Show x64 calling convention, demo'd with a call to memset(). GCC's memset is a builtin function, to disable it, use -fno-builtin. Refer to http://en.wikipedia.org/wiki/X86_calling_conventions#System_V_AMD64_ABI_convention

test_memset.c

#include <string.h>

int main() {
  memset(0x42, 42, 37);
  return 0;
}

test_memset.objdump.out

0000000000400498 <main>:
  400498:       55                      push   %rbp
  400499:       48 89 e5                mov    %rsp,%rbp
  40049c:       ba 25 00 00 00          mov    $0x25,%edx
  4004a1:       be 2a 00 00 00          mov    $0x2a,%esi
  4004a6:       bf 42 00 00 00          mov    $0x42,%edi
  4004ab:       e8 e8 fe ff ff          callq  400398 <memset@plt>
  4004b0:       b8 00 00 00 00          mov    $0x0,%eax
  4004b5:       c9                      leaveq 
  4004b6:       c3                      retq   

# arguments in left-to-right order:
# RDI, RSI, RDX