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(gcc-295.info)Constructing Calls

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Constructing Function Calls
===========================

   Using the built-in functions described below, you can record the
arguments a function received, and call another function with the same
arguments, without knowing the number or types of the arguments.

   You can also record the return value of that function call, and
later return that value, without knowing what data type the function
tried to return (as long as your caller expects that data type).

`__builtin_apply_args ()'
     This built-in function returns a pointer of type `void *' to data
     describing how to perform a call with the same arguments as were
     passed to the current function.

     The function saves the arg pointer register, structure value
     address, and all registers that might be used to pass arguments to
     a function into a block of memory allocated on the stack.  Then it
     returns the address of that block.

`__builtin_apply (FUNCTION, ARGUMENTS, SIZE)'
     This built-in function invokes FUNCTION (type `void (*)()') with a
     copy of the parameters described by ARGUMENTS (type `void *') and
     SIZE (type `int').

     The value of ARGUMENTS should be the value returned by
     `__builtin_apply_args'.  The argument SIZE specifies the size of
     the stack argument data, in bytes.

     This function returns a pointer of type `void *' to data describing
     how to return whatever value was returned by FUNCTION.  The data
     is saved in a block of memory allocated on the stack.

     It is not always simple to compute the proper value for SIZE.  The
     value is used by `__builtin_apply' to compute the amount of data
     that should be pushed on the stack and copied from the incoming
     argument area.

`__builtin_return (RESULT)'
     This built-in function returns the value described by RESULT from
     the containing function.  You should specify, for RESULT, a value
     returned by `__builtin_apply'.