Ok, I'll check this.
a snippet of a complete code will help greatly :)
~d
On Monday 02 February 2004 19:44, G Halkes wrote:
> I tried it with the mspgcc 3.2.2 release that is
> currently in the download section at sourceforge with
> the gcc 3.2.2 sources, but since setting the
> STRICT_ALIGNMENT macro to 1 solves the problems, and
> all the versions in CVS of the header file that I
> looked at (including the latest for gcc 3.4) have it
> set to 0, I think you will find the same behaviour
> with all versions of the compiler.
>
> This opinion is based on the description of the macro
> I quoted earlier.
>
> G. Halkes
>
> --- Dmitry <[email protected]> wrote:
> > hm....
> > which gcc's version/build?
> > ~d
> >
> > On Monday 02 February 2004 18:10, G Halkes wrote:
> > > Hi,
> > >
> > > What I ment was, if you use the following code:
> > >
> > > struct unaligned {
> > > char first;
> > > int second;
> > > } __attribute__((packed));
> > >
> > > union test {
> > > struct unaligned data;
> > > char cdata[3];
> > > };
> > >
> > > void function() {
> > > union test test;
> > > int data, tmp;
> > > test.cdata[0] = 0x1;
> > > test.cdata[1] = 0x2;
> > > test.cdata[2] = 0x3;
> > >
> > > data = test.data.second;
> > > memcpy(&tmp, &test.data.second, 2);
> > > }
> > >
> > > data will contain the value 0x201, and not the
> >
> > value
> >
> > > 0x302 as it should. The same goes for tmp (try it.
> >
> > I
> >
> > > did and got the wrong results). The reason the
> >
> > memcpy
> >
> > > goes wrong is because it is replaced by a single
> >
> > word
> >
> > > move instead of two byte moves.
> > >
> > > When I built gcc with the STRICT_ALIGNMENT macro
> >
> > set
> >
> > > to 1, I got the value 0x302 which is correct.
> > >
> > > G. Halkes
> > >
> > > PS: I used a printf routine to output the results
> >
> > to a
> >
> > > serial port to see the result. I removed it from
> >
> > the
> >
> > > code because it isn't standard. Just in case your
> > > wondering.
> > >
> > > >for built-ins gcc takes into account alignement.
> > > > So, if gcc knows, that something aligned by 2 it
> > >
> > > uses >world operations,
> > >
> > > > otherwise byte ones.
> > > >
> > > > Packed does not mean the structure misaligned.
> > > > It depends on data types of the structure.
> > > > For example:
> > > >
> > > > struct {
> > > > char a;
> > > > int b;
> > > > };
> > > >
> > > > isn't aligned by world boundary.
> > > >
> > > > struct { int a,b}
> > > > aligned.
> > > >
> > > > Even more -- if the structure aligned and its
> >
> > size
> >
> > > is >not even, gcc will use
> > >
> > > > world operations for thhis structure size()-1
> >
> > and
> >
> > > >byte operation for a last
> > > > byte of it.
> > >
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