The macros in this section control how arguments are passed on the stack. See the following section for other macros that control passing certain arguments in registers.
intshould actually be passed as an
int. In addition to avoiding errors in certain cases of mismatch, it also makes for better code on certain machines.
#define PUSH_ROUNDING(BYTES) (BYTES)will suffice. But on other machines, instructions that appear to push one byte actually push two bytes in an attempt to maintain alignment. Then the definition should be
#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
current_function_outgoing_args_size. No space will be pushed onto the stack for each call; instead, the function prologue should increase the stack frame size by this amount. Defining both
ACCUMULATE_OUTGOING_ARGSis not proper.
FINAL_REG_PARM_STACK_SPACE (const_size, var_size)
REG_PARM_STACK_SPACEwill only be called for libcall functions, the current function, or for a function being called when it is known that such stack space must be allocated. In each case this value can be easily computed. When deciding whether a called function needs such stack space, and how much space to reserve, GNU CC uses these two macros instead of
ACCUMULATE_OUTGOING_ARGSis defined, this macro controls whether the space for these arguments counts in the value of
REG_PARM_STACK_SPACEis defined, but the stack parameters don't skip the area specified by it. Normally, when a parameter is not passed in registers, it is placed on the stack beyond the
REG_PARM_STACK_SPACEarea. Defining this macro suppresses this behavior and causes the parameter to be passed on the stack in its natural location.
RETURN_POPS_ARGS (fundecl, funtype, stack-size)
FUNCTION_DECLthat describes the declaration of the function. From this you can obtain the DECL_MACHINE_ATTRIBUTES of the function. funtype is a C variable whose value is a tree node that describes the function in question. Normally it is a node of type
FUNCTION_TYPEthat describes the data type of the function. From this it is possible to obtain the data types of the value and arguments (if known). When a call to a library function is being considered, fundecl will contain an identifier node for the library function. Thus, if you need to distinguish among various library functions, you can do so by their names. Note that "library function" in this context means a function used to perform arithmetic, whose name is known specially in the compiler and was not mentioned in the C code being compiled. stack-size is the number of bytes of arguments passed on the stack. If a variable number of bytes is passed, it is zero, and argument popping will always be the responsibility of the calling function. On the Vax, all functions always pop their arguments, so the definition of this macro is stack-size. On the 68000, using the standard calling convention, no functions pop their arguments, so the value of the macro is always 0 in this case. But an alternative calling convention is available in which functions that take a fixed number of arguments pop them but other functions (such as
printf) pop nothing (the caller pops all). When this convention is in use, funtype is examined to determine whether a function takes a fixed number of arguments.