Path: utzoo!attcan!uunet!super!rminnich
From: rminnich@super.ORG (Ronald G Minnich)
Newsgroups: comp.arch
Subject: Re: Putting libc.a into a segment
Message-ID: <27624@super.ORG>
Date: 15 Jun 90 16:28:43 GMT
References: <383@garth.UUCP> <1990Jun2.134157.14516@oracle.com> <27411@metropolis.super.ORG> <3466@auspex.auspex.com>
Sender: news@super.ORG
Reply-To: rminnich@super.UUCP (Ronald G Minnich)
Organization: Supercomputing Research Center, Bowie, Md.
Lines: 44

In article <3466@auspex.auspex.com> guy@auspex.auspex.com (Guy Harris) writes:
>	1) if you jump into the middle of a function in "libc", it's
>	   either because a) the linker is malfunctioning, b) you
>	   overwrote code (unlikely given that it's generally
>	   write-protected) or smashed a function pointer, or c) because
>	   you were *trying* to.  In all those cases, the same thing can
>	   happen with static linking, so it's not unique to dynamic linking....
Yeah, but look, the "dynamic linking" to the kernel text segment 
always works because there is "hardware support" for it. 
"" are there because it isn't really that great, but it does work.
That is not the case for SunOS style software supported dynamic
linking. If for some reason ld.so should get hashed by something
then I can no longer run anything. Period. So the "dynamic linking" 
to the kernel is more robust (I think) because of 
hardware support, such as it is. Do we not care about having
the same degree of robustness for libraries?
   Of course it is not unique to dynamic linking; it is just that
nowadays on sunos i run ld everytime I run a program, and am thus
significantly more exposed to problems should there be a problem 
with ld.so. Oh, heck, I will say it: like a virus in ld.so. 
With the way things work now on SunOS you can instantly infect
every program on the system by changing one little file.
>	2) They're not *completely* undetectable; jumping into the
>	   middle of a function means you don't run the function prolog,
>	   don't copy the right stuff into registers, etc. so there's
>	   what I suspect is a good chance that the misbehaving program
>	   won't misbehave silently....
   Honest, I have seen this sort of thing happen. "This could 
never have worked"- except it did, for years. We really saw this
when we made the big move from -11 to VAX in 1980. 
   I can easily find linker screwups in a statically linked object 
with adb. Not so with dynamic linking. Not that this has ever
happened (well, actually, it did to me once long ago), but there
is a distinct difference in how easy it is to detect. 
   My original question stands. This list generally discusses 
getting lotsa flops, but I don't see much discussion of 
whether there should be a second look at such things as architectural
support for such things as dynamic linking. Does that mean
there should not be?
ron
-- 
Grad student, ca 1976: Gosh, the v6 kernel is < 64K! Compare it to that
                       OS/MVS hog at 400K!
Grad student, ca 1986: Look at all the good stuff in Gnu Emacs for only 600K!