>
> > root@analogic.com (Richard B. Johnson)
> > In the following include file, cmsg_data[0] is not properly declared.
> > We need to declare the first element in an array of unknown size. ANSI
> > allows cmsg_data[1], but not cmsg_data[0]. I have recompiled the kernel
> > with this change and everything is okay. I also recompiled several
> > network programs that use sockets and they compile and work.
> >
> > [erroneous patch deleted]
>
> Hum. You'll also need to fix all the length calculations that use
> sizeof(struct cmsghdr). See net/core/scm.c
>
If true, the first element of the unknown length string (the data) should
not be in that stucture. Look at the problems.........
struct foo {
char a[100];
short b[100];
long c[100];
char d[1];
} zap;
struct bar {
char a[100];
short b[100];
long c[100];
char d[0]; /* Like the original header */
} zim;
main()
{
printf("zim = %d\n", sizeof(zim));
printf("zap = %d\n", sizeof(zap));
}
The output of this program is NOT what one would expect.....
zim = 700
zap = 704
There is a 4-byte difference!! Hint. I deliberately put elements in the
order which will force a bad alignment so the compiler defaults to
filling in the holes. Using a zero-sized array will cause many problems
with portability, asside from the fact that it is "illegal". Since
much of the network code has been rewritten (and improved), it would be
a shame to not fix these reference problems.
Cheers,
Dick Johnson
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Richard B. Johnson
Project Engineer
Analogic Corporation
Voice : (508) 977-3000 ext. 3754
Fax : (508) 532-6097
Modem : (508) 977-6870
Ftp : ftp@boneserver.analogic.com
Email : rjohnson@analogic.com, johnson@analogic.com
Penguin : Linux version 2.1.15 on an i586 machine.
Warning : It's hard to remain at the trailing edge of technology.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-