Wizards' War [a war of magic numbers :-)]

[Brandon Allbery]

Expires:

Quoted from <3061 at sun.uucp> ["Re: Magic Numbers (and incredible stupidity in "cpio")"], by guy at sun.uucp (Guy Harris)...
+---------------
| > Executables using ``standard'' binary formats, i.e. a.out (PDP-11, Z8000)
| > and b.out (MC68000) use the standard magic numbers 0405, 0407, 0410, 0411.
| > Non-standard formats, like Xenix x.out (0x0206) and COFF (flames to
| > /dev/null; most systems are [ab].out) use distinctive magic numbers.
| 
| Well, VAX UNIX (32V, 4.xBSD, System III, Version 8?) also uses those magic
| numbers (with 413 added for demand paged executables on 4.xBSD), and
| probably lots of other 4.xBSD systems (Sun's does).  Does "most" mean "most
| UNIX implementations" or "most boxes running UNIX"?
+---------------

Most UN*X implementations. . .  By ``distinctive'', I meant that the magic
numbers are a dead giveaway of the OS; an executable beginning with 0x0206 is
*always* for Xenix, while 0407 could be *any* version of ``standard'' Un*x.

+---------------
| COFF seems to invert this, since the "file header" indicates what machine
| it's intended for. . . and the "UNIX header" has the 0405, 0407, 0410, 0411,
| and 0413. . . which indicates the format of the image but is machine-
| independent (modulo byte ordering).  Then again, the "file header" magic
| number seems to indicate something about the format of the executable....
+---------------

Even worse than I thought.  Xenix headers were the most portable ones I've
ever heard of or seen; I wish everyone would use x.out. . .

+---------------
| > .......... System V archives begin with the magic ``number'' "!<arch>\n".
| 
| System V, Release 2 archives, anyway; System V Release 1 had a portable
| archive format which was different from the 4.xBSD one which was the first
| one to use the "!<arch>\n" magic "number".
+---------------

Figures.  But I have no experience with V.1; we're upgrading from sys3 to
V.2.2 (and I can't wait to bring up Gnu Emacs!  :-)).

+---------------
| > Cpio archives also have magic numbers in them, but at the archive-member
| > level.
| 
| No, it has a magic number at the beginning - 070707....
+---------------

Hmmm. . . the Plexus manual shot down in flames again.  Thanks; I can at
least correct cpio(5).

+---------------
| ... "gee, we've finally caught up with 'tar' when it comes to portability"
| "cpio -c" archive.
+---------------

Bah.  For compatibility we use dd conv=swap < /dev/rmt0 | tar xvf - anyway.
Although I may use ansitar instead (if I can get around it backspacing on
raw magtape, which the P/60 can't do).

+---------------
| (Flame off, until next time a collection of stupidities this gross comes to
| light.)
| 
| 	Guy Harris
+---------------

``It won't be long now. . .''  :-)

--Brandon
-- 

			Lord Charteris (thurb)

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