Function Calls

For external functions, it is necessary to:

1. Set up the arguments for the function call.

2. Call the function.

3. Retrieve the result and do any necessary final actions.

A function call involves the following:

1. Load arguments into registers:
   • First integer argument in %edi

   • For string literal, address in %rdi using leaq (Load Effective Address, Quad):

     
      leaq  .LC4(%rip),%rdi  # addr literal .LC4
     

   • First floating argument in %xmm0

2. Execute a call instruction[PLT is the Procedure Linkage Table for dynamically linked procedures.]:

   
      call   sin@PLT
   

3. Floating results are returned in %xmm0. Integer results are returned in %eax or %rax.