lebrun@LL.MIT.EDU (Steven F. LeBrun) (02/11/91)
I am working on a SUN 4/370 Sparc computer running SunOS 4.0 and using the
GNU GCC Compiler version 1.39. I am developing code that uses the ANSI
method for passing variable length argument lists to functions. Since neither
the SUN CC compiler or the GCC compiler supplies the <stdarg.h> header file,
I wrote my own. My version of <stdarg.h> works well in most cases but there
is one function where I cannot get it to work. It appears that the arguments
are not being passed on the stack as expected. All evidence indicates
that the stdarg.h macros are accessing the section of the stack that should
contain the arguments only there are no arguments there.
The GCC documentation states that `GNU CC is normally configured to use the
same function calling convention normally in use on the target system.'
I am looking for information on the SUN's or GNU GCC's function calling
convention for C functions, especially any case that would cause the arguments
not to passed on the stack. I am also looking for information on whether
there is any GNU GCC option that will force the arguments to be passed on
the stack.
Please send any responses directly to me using my Internet Address since I
do not have access to the comp.lang.c newsgroup. I have enclosed sections of
the afflicted code including my version of <stdarg.h>. I thank you in advance
for any help that you may give.
-------------------------------------------------------------------------------
The code from my version of <stdarg.h>:
#if !defined(STDARG_H)
#define STDARG_H included
typedef char* va_list;
#define va_start(ap,alast) ap = (va_list) (((int) &alast) + sizeof(alast))
#define va_arg(ap, atype) *( (atype *) \
((ap = (va_list) \
((((int) ap) + sizeof(atype) + 0x03) & ~0x03)) \
- sizeof(atype)))
#define va_end(ap)
#endif /* If !defined(STDARG_H) */
NOTE: The `+ 0x03) & ~0x03' in va_arg() performs 4-byte boundry alignment.
This is different from the way it is done in the SUN's version of
<varargs.h> and it takes care of any argument that is smaller than
four bytes that is placed on the stack as an int.
-------------------------------------------------------------------------------
The following is the prototype of the misbehaving function:
int Get_OBJECT (LORDS_RETURN *, OBJECT_TABLE *, int, ... );
where LORDS_RETURN and OBJECT_TABLE are user defined types.
+--------------------------------------------------------------------------+
| Steven F. LeBrun MIT Lincoln Laboratory, Group 91 |
| Millstone Hill Radar |
| lebrun@ll.mit.edu (Internet) Westford, MA 01886 |
| lebruns@betel (internal) Phone:(617)-981-5742, FAX:(617)-981-5636 |
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