rcs blows up on suns (NULL dereferencing)
John Bruner
jdb at mordor.UUCP
Thu Sep 12 03:18:30 AEST 1985
In article <151 at maynard.UUCP> campbell at maynard.UUCP (Larry Campbell) writes:
>A minor point, but dereferencing zero only "works" on Vaxen that are
>running Berkeley Unix (don't know about USG). VMS sets page zero to
>no access; this is one of the few areas where I concede VMS a point
>over Unix. It catches an all-too-common programming error.
I implemented an (optional) new object format with page 0 unmapped in
VAX 4.2BSD. The changes to the kernel and a few user-level programs
(e.g. the linker) are minimal. A program in this format (which I
call Z0MAGIC (0420) or -Z format) will receive a SIGBUS if it attempts
to indirect through NULL. This has been very useful in finding
NULL-dereferencing bugs, both in locally-written code and in
distributed software.
I posted the set of changes to "net.unix-wizards" several months
ago. If you missed them and would like a copy, mail me a note.
--
John Bruner (S-1 Project, Lawrence Livermore National Laboratory)
MILNET: jdb at mordor [jdb at s1-c.ARPA] (415) 422-0758
UUCP: ...!ucbvax!dual!mordor!jdb ...!seismo!mordor!jdb
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