Re: The disappearing sys_call_table export.

Terje Eggestad
2003-05-08T12:42:13Z

What really gets to me is that *you* wrote in
(http://www.kernel.org/pub/linux/kernel/v2.5/ChangeLog-2.5.41):

3. Intercept system calls
OProfile (and intel's vtune which is similar in function) used to do this;
however what they really need is a notification on certain
events (exec() mostly). The way modules do this is store the original
function pointer, install a new one that calls the old one after storing
whatever info they need. This mechanism breaks badly in the light of
multiple such modules doing this versus modules
unloading/uninstalling their handlers (by restoring their saved pointer
that may or may not point to a valid handler anymore).
Eg the use of the export in this just a bandaid due to lack of a
proper mechanism, and also incorrect and crash prone.

So what you're saying here is not that you object to having people doing
syscall hooks, just that operating on the syscall_table symbol directly
is error prone (to which I wholeheartedly agree).

Then you reject a "proper mechanism".....

TJ

On Thu, 2003-05-08 at 11:59, Arjan van de Ven wrote:
> On Thu, May 08, 2003 at 11:58:33AM +0200, Terje Eggestad wrote:
> > I guess something like this:
> >
> > typedef int (*syscall_hook_t)(void * arg1, void * arg2, void * arg3,
> > void * arg4, void * arg5, void * arg6);
> >
> > #define HOOK_IN_FLAG 0x1
> > #define HOOK_OUT_FLAG 0x2
> >
> > opaquehandle = int register_syscall_hook(int syscall_nr, syscall_hook_t
> > hook_function, int flags);
> > int unregister(int opaquehandle);
> >
> > I'd make a stab at it if I knew that it stood a chance of getting
> > accepted.
>
> I dont think it has.
--
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Terje Eggestad mailto:terje.eggestad@scali.no
Scali Scalable Linux Systems http://www.scali.com

Olaf Helsets Vei 6 tel: +47 22 62 89 61 (OFFICE)
P.O.Box 150, Oppsal +47 975 31 574 (MOBILE)
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