On Thursday 22 February 2007 08:25, Shahar Dag wrote: > Hi > > I think that I have a dirty solution (but I must worn you that I am a > programmer, not a Linux expert) > - add global pointer to a function (the type of the function should be the > type of the function you want to call). A more elegant way (and more > complicated) would be to use non global pointer. > - initialize that pointer to NULL > - in the original function check the pointer, if it is not null call the > function pointed by the pointer > - on loading your new function, change the global pointer to the function > address (now you can also change the function or remove it by manipulating > the pointer)
That is what i did yesterday, but it is not that simple. When you load a module the kernel has to somehow know what are the symbols that were already defined in the kernel and what symbols are in your module. He does that dynamically using a symbol table. The pointer needs to be exported. In addition, kernel functions, especially that one are re-entrant and many times locking is not an option. I will probably have to employ some circular buffer with no locking and later a background thread will crunch these. > > Have fun > Shahar > ___________________________________________________________________________ >__________________ > > I am looking for old Vinyl record. > If you have any that you don't need please send me mail to > [EMAIL PROTECTED] > > Thanks > Shahar > > ----- Original Message ----- > From: "Tzahi Fadida" <[EMAIL PROTECTED]> > To: "Baruch Even" <[EMAIL PROTECTED]> > Cc: "Linux-IL" <linux-il@linux.org.il> > Sent: Wednesday, February 21, 2007 14:46 > Subject: Re: Decorating a kernel function > > On Wednesday 21 February 2007 08:19, Baruch Even wrote: > > * Tzahi Fadida <[EMAIL PROTECTED]> [070221 02:38]: > > I'm not aware of a way to do what you ask (redirect the function to you > > and be able to call it), you can however look at kprobe which is part of > > the kernel. kprobe allows you to stick trap points into the kernel and > > be called at that point, I don't remember the exact name but they have a > > method to stick the probe at the end of the function (and also at the > > beginning or arbitrary location). > > > > I've used this method to trace methods and it's fairly expensive since > > it uses int3 trap points to do its work but if performance is not > > critical for you it should be fine. > > kprobe is what i was looking for. Actually, jprobe so i cal also view the > function parameters i am attaching to. The problem is that kprobe does not > appear on the uml(user mode linux) list in menuconfig which probably means > it > is not supported there. -> i need to compile a real kernel or use vmware or > something like that. I prefer to continue to use uml. > Let's say i do wish to change the kernel code. How do i add a code that > will refer to my module once it is loaded? I.e. i wish to add a stub in > that function in the kernel that will call a function in my module if it is > up. > > > Baruch -- Regards, Tzahi. -- Tzahi Fadida Blog: http://tzahi.blogsite.org | Home Site: http://tzahi.webhop.info WARNING TO SPAMMERS: see at http://members.lycos.co.uk/my2nis/spamwarning.html ================================================================To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
