Date: Mon, 16 Apr 2012 14:28:50 +0200 From: Sebastian Huber <sebastian.huber@embedded-brains.de> To: freebsd-hackers@freebsd.org, freebsd-arm@freebsd.org Subject: XDR Library and Short Enums Message-ID: <4F8C1082.3020801@embedded-brains.de>
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Hi,
the XDR library implementation of xdr_enum() is currently:
/*
* XDR enumerations
*/
bool_t
xdr_enum(XDR *xdrs, enum_t *ep)
{
enum sizecheck { SIZEVAL }; /* used to find the size of an enum */
/*
* enums are treated as ints
*/
/* LINTED */ if (sizeof (enum sizecheck) == sizeof (long)) {
return (xdr_long(xdrs, (long *)(void *)ep));
} else /* LINTED */ if (sizeof (enum sizecheck) == sizeof (int)) {
return (xdr_int(xdrs, (int *)(void *)ep));
} else /* LINTED */ if (sizeof (enum sizecheck) == sizeof (short)) {
return (xdr_short(xdrs, (short *)(void *)ep));
} else {
return (FALSE);
}
}
The enum_t is defined as:
typedef int32_t enum_t;
This is problematic with short enums (variable sized enums). I case of short
enums sizeof (enum sizecheck) would be 1. The ARM EABI lets you a choice
between two alternatives described in the document issued by ARM. See also
section 7.1.3 "Enumerated Types"
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042d/IHI0042D_aapcs.pdf
How would you implement and use the XDR library with short enums? The
xdr_enum() can be easily changed to:
/*
* XDR enumerations
*/
bool_t
xdr_enum(XDR *xdrs, enum_t *ep)
{
/*
* enums are treated as ints
*/
/* LINTED */ if (sizeof (enum_t) == sizeof (long)) {
return (xdr_long(xdrs, (long *)(void *)ep));
} else /* LINTED */ if (sizeof (enum_t) == sizeof (int)) {
return (xdr_int(xdrs, (int *)(void *)ep));
} else /* LINTED */ if (sizeof (enum_t) == sizeof (short)) {
return (xdr_short(xdrs, (short *)(void *)ep));
} else {
return (FALSE);
}
}
The problem is in the XDR library usage. An example is this (rpc_msg.h):
enum msg_type {
CALL=0,
REPLY=1
};
How would you fix this? What about
enum msg_type {
CALL=0,
REPLY=1,
_MSG_TYPE_INVALID = 0xffffffff
};
?
--
Sebastian Huber, embedded brains GmbH
Address : Obere Lagerstr. 30, D-82178 Puchheim, Germany
Phone : +49 89 18 90 80 79-6
Fax : +49 89 18 90 80 79-9
E-Mail : sebastian.huber@embedded-brains.de
PGP : Public key available on request.
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