[ECOS] Packed on a Arm Evaulation Board

[ECOS] Packed on a Arm Evaulation Board

[jens.ohlund]

Hi!

I'm having a problem, I can't find out how to align data on even bytes.

That is, if I create a struct with 4 uint8 (unsigned char) I want the struct to be 8 bytes in size.

Why ? It's a requirment for a jvm I try to run. I've tried with __attribute__ ((packed)), which I thought worked when I tried to
make a struct with one byte, one short and one interger.
But I had lots of "funny" errors so I checked it up a bit more just to se that that 2 unsigned chars used only 16 bit together, not
16 bits EACH.

Anybody got any idea how I should do instead ?

yours
Jens Ohlund

RE: [ECOS] Packed on a Arm Evaulation Board

[Gary Thomas]

Try

  struct ABC { ...whatever... } __attribute__ ((aligned(1), packed));

On 20-Jun-00 jens.ohlund@secrc.abb.se wrote:
> Hi!
> 
> I'm having a problem, I can't find out how to align data on even bytes.
> 
> That is, if I create a struct with 4 uint8 (unsigned char) I want the struct to be 8 bytes in
> size.
> 
> Why ? It's a requirment for a jvm I try to run. I've tried with __attribute__ ((packed)), which I
> thought worked when I tried to
> make a struct with one byte, one short and one interger.
> But I had lots of "funny" errors so I checked it up a bit more just to se that that 2 unsigned
> chars used only 16 bit together, not
> 16 bits EACH.
> 
> Anybody got any idea how I should do instead ?
> 
> yours
> Jens Ohlund
> 
> 
> 

Re: [ECOS] Packed on a Arm Evaulation Board

[Jonathan Larmour]

Gary Thomas wrote:
> 
> Try
> 
>   struct ABC { ...whatever... } __attribute__ ((aligned(1), packed));

I've found from experience that you can't mix the aligned and packed
attributes. Also the aligned attribute only describes the alignment of the
structure, not of the fields inside it (For Gary's benefit, read the thread
subject "eCos 1.3.5 branch" around 4th/5th May from our internal lists).

Individual members of a struct can also
have __attribute__((packed)) on them, e.g. from gcc.info:

Here is a structure in which the field `x' is packed, so that it
immediately follows `a':  

  struct foo
  { 
    char a;
    int x[2] __attribute__ ((packed));
  };

Jifl
-- 
Red Hat, 35 Cambridge Place, Cambridge, UK. CB2 1NS  Tel: +44 (1223) 728762
"Plan to be spontaneous tomorrow."  ||  These opinions are all my own fault

Re: [ECOS] Packed on a Arm Evaulation Board

[Jesper Skov]

Try this:

  struct snejs
  {
    char bokstav1 __attribute__ ((aligned(2));
    char bokstav2 __attribute__ ((aligned(2));
    char bokstav3 __attribute__ ((aligned(2));
    char bokstav4 __attribute__ ((aligned(2));
    short siffra1 __attribute__ ((aligned(2));
    long siffra2;
  } mojs __attribute__ ((packed);


Jesper

Re: [ECOS] Packed on a Arm Evaulation Board

[Sergei Organov]

Try this:

struct snejs
{
  char bokstav1 __attribute__((aligned(2));
  char bokstav2 __attribute__((aligned(2));
  char bokstav3 __attribute__((aligned(2));
  char bokstav4 __attribute__((aligned(2));
  short siffra1;
  long siffra2;
} mojs;

or even this:

struct snejs
{
  char bokstav1; char foo1;
  char bokstav2; char foo2;
  char bokstav3; char foo3;
  char bokstav4;
  short siffra1;
  long siffra2;
} mojs;


jens.ohlund@secrc.abb.se writes:
> Hi !
>
> Well, didn't work. The code looks like:
>   struct snejs
>   {
>     char bokstav1;
>     char bokstav2;
>     char bokstav3;
>     char bokstav4;
>     short siffra1;
>     long siffra2;
>   } mojs;
>
> And I tried to put the __attribute__ before snejs and after mojs, I tried to
> change the aligned(1) to aligned(2) as well.
>
> yours Jens
>
>
>
>
>
> ecos-discuss-owner@sourceware.cygnus.com 2000-06-20 16:36
>
>
> To: jens.ohlund@secrc.abb.se cc: ecos-discuss@sourceware.cygnus.com Subject:
> RE: [ECOS] Packed on a Arm Evaulation Board
>
> Security Level:?  Internal
>
>
> Try
>
>   struct ABC { ...whatever... } __attribute__ ((aligned(1), packed));
>
> On 20-Jun-00 jens.ohlund@secrc.abb.se wrote:
> > Hi!
> >
> > I'm having a problem, I can't find out how to align data on even bytes.
> >
> > That is, if I create a struct with 4 uint8 (unsigned char) I want the struct
> >to be 8 bytes in size.
> >
> > Why ? It's a requirment for a jvm I try to run. I've tried with
> >__attribute__ ((packed)), which I thought worked when I tried to make a
> >struct with one byte, one short and one interger.  But I had lots of "funny"
> >errors so I checked it up a bit more just to se that that 2 unsigned chars
> >used only 16 bit together, not 16 bits EACH.
> >
> > Anybody got any idea how I should do instead ?
> >
> > yours Jens Ohlund
> >
> >
> >

RE: [ECOS] Packed on a Arm Evaulation Board

[jens.ohlund]

Hi !

Well, didn't work. The code looks like:
  struct snejs
  {
    char bokstav1;
    char bokstav2;
    char bokstav3;
    char bokstav4;
    short siffra1;
    long siffra2;
  } mojs;

And I tried to put the __attribute__  before snejs and after mojs, I tried to change the aligned(1) to aligned(2) as well.

yours
Jens





ecos-discuss-owner@sourceware.cygnus.com
2000-06-20 16:36


To:   jens.ohlund@secrc.abb.se
cc:   ecos-discuss@sourceware.cygnus.com
Subject:  RE: [ECOS] Packed on a Arm Evaulation Board

Security Level:?         Internal


Try

  struct ABC { ...whatever... } __attribute__ ((aligned(1), packed));

On 20-Jun-00 jens.ohlund@secrc.abb.se wrote:
> Hi!
>
> I'm having a problem, I can't find out how to align data on even bytes.
>
> That is, if I create a struct with 4 uint8 (unsigned char) I want the struct to be 8 bytes in
> size.
>
> Why ? It's a requirment for a jvm I try to run. I've tried with __attribute__ ((packed)), which I
> thought worked when I tried to
> make a struct with one byte, one short and one interger.
> But I had lots of "funny" errors so I checked it up a bit more just to se that that 2 unsigned
> chars used only 16 bit together, not
> 16 bits EACH.
>
> Anybody got any idea how I should do instead ?
>
> yours
> Jens Ohlund
>
>
>