ye@henri.ucsb.edu (Hong Ye) (03/19/91)
Following piece of code looks to be perfectly innocent. It runs perfectly on Sun-3 indeed. But it produces weird results on Sun-4 and DEC2100. I guess the compiler on Sun-4 or DEC uses a different calling convention. Could anybody tell me what I am doing wrong? Please reply through mail. #include <stdio.h> #define argA 0xAAAAAAAA #define argB 0xBBBBBBBB #define argC 0xCCCCCCCC main() { printf("Original:\n"); printf("\t%08X\n\t%08X\n\t%08X\n",argA,argB,argC); fake_printf(argA,argB,argC,0); } /* main */ fake_printf(args) int args; { internal_printf(&args); } /* fake_printf */ internal_printf(args) int *args; { printf("Inside Printf:\n"); while (*args) { printf("\t%08X\n",*args); args++; } } /* internal_printf */
basile@soleil.cea.fr (Basile STARYNKEVITCH) (03/28/91)
Your code is implicitly built on the assumption that arguments are passed on a stack (such as Mc680x0 machines, eg. Sun3s). Actually this is false on many RISC machines, such as Sun4s. On SPARC machines, arguments are passed in registers (each calling frame is actually a set of registers - there are 32 sets of 24 (overlapping) registers), so calls (especially to leaf routines) is really fast. The system flushs the register set to the (memory) stack when it is full. On Vaxen, a calling frame is supported by hardware (on the calling stack). By the way, your code is neither lint nor Ansi-C (or C++) compliant. For this reason, varargs (with setjmp, etc) facilities are peculiar to each compiler&machine (and their interface should be and is normalized in Ansi-C or K&R-C or C++). On Sun3, varargs are plain C (machine and compiler dependant) macros. On Sun4, varargs use special identifiers __builtin_va_alist & __builtin_va_arg_incr (see /usr/include/varargs.h) known by the compiler. On Vaxen, varargs call a special routine (assembly coded in libc.a). By the way, C is lacking of the varargs reciprocial: calling a routine (given by its adress) with a variable sized list of arguments. More specifically, i'm seeking for a "varapply" capability to call a routine whose argument list is known at run time - e.g. given by a null terminated array of (argument size, argument adress) tuples. Basile STARYNKEVITCH Commissariat a l' Energie Atomique DRN/DMT/SERMA C.E. Saclay 91191 GIF/YVETTE CEDEX France email: basile@soleil.saclay.cea.fr