Re: library symbols

From: Michele Andreoli (
Date: Thu Dec 14 2000 - 20:22:13 CET

On Thu, Dec 14, 2000 at 02:53:48PM +0100, Dumas Patrice nicely wrote:

> Always on the same subject, has anyone ever heard about a way to
> complement libraries, that is you have a library loaded in the system,
> and than you add some more code to the library, dynamically (a
> dynamically growing dynamic library....).

I know only a trick based on the /etc/ file.
If you put a library reference in this file, it will be
loaded FIRTS of all other. So, If you develope, for example,
a rustic math library and pre-load it in this way, your simbols
take precedence.

Anyway, the your is a not-problem: if you develope new functions,
you can just put the new library in /lib.

But my feel about the libc is a little different. In theory, a
kernel module can access directly to the kernel resource.
In other words, the kernel itself can act like a big library.
A kernel module can easily take input from a file in /proc; the
same, it can return output in a file in /proc. I saw
more example of that in the never-too-praised A. Rubini's book.

So, one can develope a sort of /proc/gateway-in and
/proc/gateway-out. You put with a script a command on the "in"
file and the module put its answer on the "out" file.

Example are routing table manipulation: in theory, it is possible
to remove command like "ifconfig" and "route" from muLinux.
You can replace ifconfig with a script which echo its command-line
parameter on the "in" file. The kernel-module listen to
the gateway-in and execute the relevant kernel code.

No mistery in that: libc is only a C gateway to the kernel
internals, isnt true? With this trick, a lot of system command
can be replaced with script 1-2 lines long!

The "hostname" command in muLinux works exactly in this way:
it simply echo the hostname on the kernel gateway

This is also the mechanism used by the asmutils, but using


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