Basic ABI: SysV i386

Out-of-Process Method Invocation:
   Caller:
      eax: pointer to parameter info block (PIB)

      Call the 32-bit address stored at 0x7fff0000 to invoke the method.
      
      Upon return:
      ebx, esi, edi, ebp, esp: preserved
      eax: pointer to exception, or NULL if none.
           If there is an exception, the user part of the syscall
           function will search for an exception handling function
           that covers the calling address.  If none is found,
           it will assume that it is a language without exception
           handling, and return the exception to the caller in eax.
      ecx: length of exception segment, if any
      edx: may be clobbered
      
   Callee:
      eax: pointer to PIB
      edx: pointer to caller information struct, if such was
           requested

      Jump to the 32-bit address stored at 0x7fff0004 to return.
      
      Upon return:
      eax: pointer to exception, or NULL if none.
      ecx: length of exception segment, if any
      ebx, esi, edi, ebp, esp: should be preserved
      edx: may be clobbered