* Re: dynamicly/staticly linked binaries
2004-09-06 16:55 dynamicly/staticly linked binaries heap
@ 2004-09-06 16:28 ` Jan-Benedict Glaw
0 siblings, 0 replies; 2+ messages in thread
From: Jan-Benedict Glaw @ 2004-09-06 16:28 UTC (permalink / raw)
To: heap; +Cc: linux-c-programming
[-- Attachment #1: Type: text/plain, Size: 3392 bytes --]
On Mon, 2004-09-06 16:55:03 -0000, heap <heap@fbnet.org>
wrote in message <40450.212.113.164.104.1094489703.squirrel@www.fbnet.org>:
> Hello, could anyone tell me what's the difference between the dynamicly
> and staticly linked binaries? As far as I can tell, there are security
> risks implied, but I can't see in what way.
Programs use functions like "printf()". These functions are placed into
libraries (so that they can be accessed by all programs, since they all
expect "printf()" to do the very same thing.
Dynamically linked programs use a library which is liked into the
program at program's start-up time. Eg. you type in "ls", hit the Enter
key and this is what happens:
- shell interpreter fork()s; the child then exec()s the "ls"
program.
- Kernel loads the first few bytes of it to determine it's file
type (lets assume it's an ELF program).
- The ELF format handler loads the program's "interpreter",
/bin/ld-linux.so.2 . This program looks into the binary to
start and determines which dynamically libraries need to be
loaded (cf. "ldd `which ls`").
- After the "interpreter" finally linked the binary with it's
needed libraries, the program is ready for execution, the
interpreter calls libc's startup functions (which first call
all constructor functions, does initialization jobs and the
like) and finally calls main().
If you (or your distribution's people) ever find a bug in one of these
dynamically linked libraries, it can be exchanged so that all programs
using it are fixed at once. While the program binaries are comparably
small (since they don't ship all those bloated libs with them), you pay
a prize: dynamically linked programs need some time after being started
to get finally linked together.
Statically linked programs can be executed and are instantly ready to
run, since they shil all the libs they need. However, these programs are
a lot larger, but have a quicker start-up time. Also, if you find a bug
in one of the used libs, you need to exchange all binaries which are
statically linked with that lib.
Dynamic Static
-------------------------------------------------------------------------
Program size on small large
harddisk
Program size in smaller, since the larger (because there's
RAM OS may decide to no connection between
only load a dynamic two identical libs in
lib's text segment two different programs).
(the "code") once.
Bug in lib Exchange the lib and Re-link all programs using
you're done with it. the lib and exchange them.
Start-up time Need some time to do Instantly ready to run.
final link, but that
can be cut down with
some tricks.
Traceability With some tricks, you Doesn't help you in reverse
can trace what a engineering or debugging,
program does with it's but you can still do that
libraries--may help with standard GNUish tools.
in reverse engineering
and debugging.
So that's an overview, but there's a lot to add.
MfG, JBG
--
Jan-Benedict Glaw jbglaw@lug-owl.de . +49-172-7608481 _ O _
"Eine Freie Meinung in einem Freien Kopf | Gegen Zensur | Gegen Krieg _ _ O
fuer einen Freien Staat voll Freier Bürger" | im Internet! | im Irak! O O O
ret = do_actions((curr | FREE_SPEECH) & ~(NEW_COPYRIGHT_LAW | DRM | TCPA));
[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 189 bytes --]
^ permalink raw reply [flat|nested] 2+ messages in thread