RE: Alignment of stack traces

["Boehm, Hans" <hans_boehm at hp dot com>]

My patch was actually trying to deal with the fact that pointers and jlongs
may not be the same size.  But yours is simpler, and I prefer it.  Here's a
slightly revised version that fixes a problem with a forward reference to p.
It built and passed a superficial test on Linux/X86.

I would vote for putting it in both branches now, and reverting it in the
development tree if we decide to do something more substantial.

Hans

Index: natThrowable.cc
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/lang/natThrowable.cc,v
retrieving revision 1.8
diff -r1.8 natThrowable.cc
68c68
<       // ???  Might this cause a problem if the byte array isn't aligned?
---
>       // We copy the array below to deal with alignment issues.
86,87c86,89
<   void **p = (void **)elements (stackTrace);
<   int depth = stackTrace->length / sizeof p[0];
---
>   int depth = stackTrace->length / sizeof(void *);
>   void *p[depth];
> 
>   memcpy (p, elements (stackTrace), stackTrace->length);


> -----Original Message-----
> From: Andrew Haley [mailto:aph@redhat.com]
> Sent: Thursday, March 01, 2001 12:26 PM
> To: Boehm, Hans
> Cc: 'Jeff Sturm'; Bryce McKinlay; 'java@gcc.gnu.org'
> Subject: RE: Alignment of stack traces
> 
> 
> Boehm, Hans writes:
>  > Are there enough other uses for this that it's worth doing?
>  > 
>  > Java primitive arrays almost fit the bill here, except 
> that there's no way
>  > to say "an array of pointer-sized integers.  Java object 
> arrays would work,
>  > but add extra scanning time.
>  > 
>  > For now I'm using an array of Java longs, which doesn't 
> appear to have
>  > broken anything on Itanium.  But I haven't even rebuilt on X86 yet.
> 
> An array of Java longs ought to do it, but it may not always work; a
> pointer doesn't have to be the same size as a jlong.
> 
> The cleanest way to fix this is probably to copy the data from the
> byte array to an array of pointers when it's time to print the stack
> trace.  The difference in efficiency is so marginal as not to be worth
> worrying about.
> 
> Is this OK?
> 
> Andrew.
> 
> 2001-03-01  Andrew Haley  <aph@redhat.com>
> 
> 	* java/lang/natThrowable.cc (printRawStackTrace): Copy the
> 	stackTrace buffer to a correctly aligned pointer array.
>  
> Index: java/lang/natThrowable.cc
> ===================================================================
> RCS file: /cvs/gcc/gcc/libjava/java/lang/natThrowable.cc,v
> retrieving revision 1.8
> diff -u -r1.8 natThrowable.cc
> --- natThrowable.cc	2000/12/22 06:19:24	1.8
> +++ natThrowable.cc	2001/03/01 20:23:04
> @@ -83,8 +83,9 @@
>    if (!stackTrace)
>      return;
>  
> -  void **p = (void **)elements (stackTrace);
>    int depth = stackTrace->length / sizeof p[0];
> +  void *p[depth];
> +  memcpy (p, elements (stackTrace), stackTrace->length);
>  
>    _Jv_name_finder finder (_Jv_ThisExecutable ());
>  
>