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From: jwright@cfht.hawaii.edu (Jim Wright)
Newsgroups: comp.sys.hp
Subject: Re: X11R4: Problem executing xgc(demo) and xrn6.8(comp.sources.x)
Message-ID: <jwright.649751983@quonset>
Date: 4 Aug 90 06:39:43 GMT
References: <2297@s3.ireq.hydro.qc.ca>
Sender: news@uhccux.uhcc.Hawaii.Edu
Lines: 47

lamarche@ireq.hydro.qc.ca writes:
>I have compiled X11R4 (original tapes) on my hp360 machine 
>running HP-UX 7.0. Everything went fine. Then I compiled
>xrn (6.8) from comp.sources.x, everything went fine also.
>When I run xgc ( in mit/demo ) or xrn both programs abort.
>I get the message:
>	Error: Cannot perform realloc
>Does anyone have an idea of a solution to this problem?

I was able to beat this same bug, with lots of email help from some folks
at HP.  (Sorry, can't find names right now.)  The "problem" is that X may
call one of the alloc() routines with a request for zero bytes of memory,
but expects to get a valid pointer back.  I consider this a bug in X and
not in HP's alloc.

To fix this, you have to define the pre-processor symbol MALLOC_0_RETURNS_NULL
and recompile *ALL* of X as well as all of your applications.  This worked
wonders for me.  Below are a bits from two pertinent files.

/*---------------- extract from site.def file ----------------*/
STD_DEFINES = -Wc,-Nd4000,-Ns3000 -DMALLOC_0_RETURNS_NULL -DSYSV

/*---------------- extract from X11/Xlibos.h -----------------*/

/*** char *malloc(), *realloc(), *calloc(), *alloca(); *** FIXED - jrw ***/
void *malloc(), *realloc(), *calloc(), *alloca();

/*
 * Note that some machines do not return a valid pointer for malloc(0), in
 * which case we provide an alternate under the control of the
 * define MALLOC_0_RETURNS_NULL.  This is necessary because some
 * Xlib code expects malloc(0) to return a valid pointer to storage.
 */
#ifdef MALLOC_0_RETURNS_NULL
# define Xmalloc(size) malloc(((size) > 0 ? (size) : 1))
# define Xrealloc(ptr, size) realloc((ptr), ((size) > 0 ? (size) : 1))
# define Xcalloc(nelem, elsize) calloc(((nelem) > 0 ? (nelem) : 1), (elsize))
#else
# define Xmalloc(size) malloc((size))
# define Xrealloc(ptr, size) realloc((ptr), (size))
# define Xcalloc(nelem, elsize) calloc((nelem), (elsize))
#endif

--
Jim Wright
jwright@quonset.cfht.hawaii.edu
Canada-France-Hawaii Telescope Corp.