Alignment issues on sparc in convert_bitmap in wrc/newstruc.c

[Warren_Baird at cimmetry.com]

I've got a solution to some of the alignment problems in wrc for
sparc-solaris, but I wanted to bounce them off the -devel list before
submitting a patch.  I'm going to describe the problem first, and then
my solution to it.

Sparc-solaris machines are a little pickier about byte alignment than
x86-linux machines are (don't know about x86-solaris - haven't played
with it).  Basically things like ints need to be aligned on word
boundaries, or else you get a bus error when you try to access them.
The following code fragment:

  struct myStruct {
        int a;
        int b;
  };

  int main() {
    int tmp = (int) malloc(sizeof(struct myStruct)+2);
    tmp += 2;
    struct myStruct *myS = (struct myStruct *) tmp;
    myS->a = 0x12345678;
    return 0;
  }

Causes a bus error on the assignment into myS->a.  Commenting out the
tmp += 2 line of course solves the problem.

Unfortunately this kind of thing is happening in a few places in
wrc/newstruc.c - in calls to convert_bitmap.  The actual bitmap data
is 22 bytes into the raw data from the resource file.  The raw data is
properly aligned on a word boundary, but the bitmap data isn't.  The
current process is to call convert_bitmap on the data, and then
memcopy/memmove it into it's final resting place.  The final resting
place *is* word-aligned.

The solution I've taken in my code is to reverse the order - first I
memcopy/memmove the bitmap data, and *then* I call convert_bitmap.
This seems to solve the problems on sparc-solaris, and I can't see how
it could hurt on Linux (but I haven't had a chance to test it on Linux
yet).

Does this make sense?  Does anyone have a better suggestion?

Warren