Alignment problems

From	jacob navia <jacob@spamsink.net>
Newsgroups	comp.lang.c
Subject	Alignment problems
Date	2011-12-01 01:05 +0100
Organization	lccwin
Message-ID	<jb6gbf$58a$1@speranza.aioe.org> (permalink)

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I am trying to test the containers library in different environments

One of those is SUN sparc, that crashes when a double is accessed
in an address not multiple of 8. I got an access to an old one:

: ~/ccl ; uname -a
SunOS 5.9 Generic_118558-25 sun4u sparc SUNW,Sun-Fire-V210

Now, I have a list container with elements that
have this structure:

typedef struct _ListElement {
     struct _ListElement *Next;
     char Data[MINIMUM_ARRAY_INDEX]; // Generic storage...
} ListElement;


If I store double data in the "Data" member the machine will
crash since apparently it is a 32 bit SPARC, and the start of Data
is NOT aligned to an eight byte boundary.

One solution (albeit very ugly) is:

typedef struct _ListElement {
     struct _ListElement *Next;
     double alignment1;
     char Data[MINIMUM_ARRAY_INDEX]; // Generic storage...
} ListElement;

This works. The compiler will correctly align "Data" and I
can safely store doubles into it. But this solutions is VERY
expensive since for EACH element I am spending 8 bytes
in alignment...

Is there another solution?

The "Data" member MUST be the last since it is a variable length
structure.


Thanks in advance for any pointers.

jacob

P.S. If anyone knows that system, gcc warns me

warning: implicit declaration of function 'snprintf'

I do include stdio.h...

What else should I include for getting snprintf?
Note that the link works, the function exists.
My compile options are:

gcc -std=c99 -I. -g -DUNIX  -c  sequential.c

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Alignment problems jacob navia <jacob@spamsink.net> - 2011-12-01 01:05 +0100
  Re: Alignment problems Ian Collins <ian-news@hotmail.com> - 2011-12-01 13:15 +1300
  Re: Alignment problems pacman@kosh.dhis.org (Alan Curry) - 2011-12-01 02:57 +0000
  Re: Alignment problems gordonb.hpln0@burditt.org (Gordon Burditt) - 2011-11-30 21:27 -0600
  Re: Alignment problems jacob navia <jacob@spamsink.net> - 2011-12-01 13:38 +0100
    Re: Alignment problems pacman@kosh.dhis.org (Alan Curry) - 2011-12-01 20:38 +0000
      Re: Alignment problems jacob navia <jacob@spamsink.net> - 2011-12-01 21:50 +0100
        Re: Alignment problems Ian Collins <ian-news@hotmail.com> - 2011-12-02 10:27 +1300
          Re: Alignment problems Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-12-04 00:23 +0000
            Re: Alignment problems Ian Collins <ian-news@hotmail.com> - 2011-12-04 13:31 +1300
        Re: Alignment problems ImpalerCore <jadill33@gmail.com> - 2011-12-01 14:34 -0800
  Re: Alignment problems "BartC" <bc@freeuk.com> - 2011-12-01 13:46 +0000
    Re: Alignment problems Keith Thompson <kst-u@mib.org> - 2011-12-01 14:15 -0800
      Re: Alignment problems David Thompson <dave.thompson2@verizon.net> - 2012-01-19 02:44 -0500
  Re: Alignment problems "James" <no@spam.invalid> - 2011-12-01 19:43 -0800
  Re: Alignment problems "Brain" <Brian@myhome.com> - 2011-12-04 02:47 -0600
    Re: Alignment problems Keith Thompson <kst-u@mib.org> - 2011-12-04 08:26 -0800
      Re: Alignment problems Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-12-08 00:12 +0200
        Re: Alignment problems Keith Thompson <kst-u@mib.org> - 2011-12-07 22:31 -0800
          Re: Alignment problems lovecreatesbeauty <lovecreatesbeauty@gmail.com> - 2011-12-08 21:43 -0800
            Re: Alignment problems Keith Thompson <kst-u@mib.org> - 2011-12-09 01:31 -0800
              Re: Alignment problems Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-12-09 14:15 +0200

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