include/minix/compiler.h

   1 /* Definitions for compiler-specific features. */
   2
   3 #ifndef _MINIX_COMPILER_H
   4 #define _MINIX_COMPILER_H
   5
   6 /*===========================================================================*
   7  *                          Compiler overrides                               *
   8  *===========================================================================*/
   9 /* ACK */
  10 #ifdef __ACK__
  11 #include <minix/compiler-ack.h>
  12 #endif
  13
  14 /*===========================================================================*
  15  *                             Default values                                *
  16  *===========================================================================*/
  17 /*
  18  * cdecl calling convention expects the callee to pop the hidden pointer on
  19  * struct return. For example, GCC and LLVM comply with this (tested on IA32).
  20  */
  21 #ifndef BYTES_TO_POP_ON_STRUCT_RETURN
  22 #define BYTES_TO_POP_ON_STRUCT_RETURN $4
  23 #endif
  24
  25 /*
  26  * cdecl calling convention requires to push arguments on the stack in a
  27  * reverse order to easily support variadic arguments. Thus, instead of
  28  * using the proper stdarg.h macros (that nowadays are
  29  * compiler-dependant), it may be tempting to directly take the address of
  30  * the last argument and considering it as the start of an array. This is
  31  * a shortcut that avoid looping to get all the arguments as the CPU
  32  * already pushed them on the stack before the call to the function.
  33  *
  34  * Unfortunately, such an assumption is strictly compiler-dependant and
  35  * compilers are free to move the last argument on the stack, as a local
  36  * variable, and return the address of the location where the argument was
  37  * stored, if asked for. This will break things as the rest of the array's
  38  * argument are stored elsewhere (typically, a couple of words above the
  39  * location where the argument was stored).
  40  *
  41  * Conclusion: if unsure on what the compiler may do, do not make any
  42  * assumption and use the right (typically compiler-dependant) macros.
  43  */
  44
  45 #ifndef FUNC_ARGS_ARRAY
  46 #define FUNC_ARGS_ARRAY 0
  47 #endif
  48
  49 #endif /* _MINIX_COMPILER_H */