The LD_* vars (was Re: LD_ hole)
Justin Mason (jmason@iona.ie)
Thu, 16 Dec 1993 12:59:43 +0000
In your message of Wed, 15 Dec 1993 13:18:14 MST, you say:
>> c) delete any environment varable that begins with LD_
> Most people have said this for obvious reasons, but the ld manpage says
>that will not search anything (for suid binaries) other than the trusted
>paths for dynamically linked libraries even if LD_LIBRARY_PATH is set. Is
>this statement false? Is there a way around it? Is LD_PRELOAD_PATH documented
>anywhere? :-)
Okay, here's all the under-documented stuff about LD_* variables, mostly
from my own and other people's hacks on SunOS 4.1.2:
> 11:55:16 - 54 #...; strings /lib/ld.so | grep LD_
> LD_LIBRARY_PATH
> LD_TRACE_LOADED_OBJECTS
> LD_PROFILE
> LD_PRELOAD
> LD_SYMBOLS_PUBLIC
LD_LIBRARY_PATH: you know what this is.
LD_PRELOAD: the name of file(s) to include, a la LD_LIB_PATH libraries.
It's a colon-separated list. On Solaris 2.x, this list is
space-separated (Linkers And Libraries Manual, p.21).
LD_TRACE_LOADED_OBJECTS: set this, and it shows the expected shared libs
every time you run a command. Not very insecure, but now you know
how ldd(8) works! ;)
LD_PROFILE: I have no idea -- Caspar H. Dik might (he knows these things).
LD_SYMBOLS_PUBLIC: prints the path to the runtime linker, ld.so(8), in use.
It only seems to have an effect when you use ldd(8).
There's more on Solaris 2.x: from the Linkers And Libraries Manual:
LD_BIND_NOW: set this, and ld.so will check for unresolved function references
at run-time. Ordinarily, it delays resolving them until the function is
invoked; see p.22.
LD_BINDINGS: "ld.so displays the actual symbol resolution", p.27.
There's also LD_SIGNAL, LD__OUTPUT (may just be LD_OUTPUT), LD_BIND_NOT (!),
LD_WARN. God only knows what they do. Then there's the regulars:
LD_LIBRARY_PATH, LD_TRACE_LOADED_OBJECTS, LD_PROFILE and LD_PRELOAD.
Anyway, that's all I know -- one of the shared-lib gurus (Caspar H. Dik or
Oleg Kibirev) could probably fill in the rest.
--
Justin Mason (Iona Technologies' unix caretaker, fixer-upper and disk-filler)
email addr: <jmason@iona.ie> http://www.iona.ie/hyplan/jmason.htm
"I was an infinitely hot and -><- (disclaimer: these are my opinions,
dense dot." -- Mark Leyner -><- usually not those of my employers)