Messages in this thread | | | Date | Mon, 14 Nov 2005 11:24:57 +0530 | From | Prasanna S Panchamukhi <> | Subject | Re: [PATCH 19/21] i386 Kprobes semaphore fix |
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> > Let me stress that if you are running on modified segment state, you > > have no way to safely determine the virtual address on which you took an > > instruction trap (int3, general protection, etc..). If you can't > > determine the virtual address safely, you can't back out your code patch > > to remove the breakpoint. At this point, you can't execute the next > > Kernel kprobes solves this by executing the code out of line. I don't know > how they want to do that in user space though (need a safe address for that), > but somehow that can be likely done.
In case of user space probes we adopt a similar method for executing the code out-of-line. In user space probes we find free space in the current process address space and copy the original instruction to that location and execute that instruction from that location. User processes use stack space to store local variables, agruments and return values. Normally the stack space either below or above the stack pointer indicates the free stack space. Also in case of no stack free space, we can expand the process stack, copy the instruction and execute the instruction from that location. Detials about this method is discussed on systemtap mailing lists. URL is below.
http://sourceware.org/ml/systemtap/2005-q3/msg00542.html
Please let me know if you have any other solution to the above problem.
Thanks Prasanna -- Prasanna S Panchamukhi Linux Technology Center India Software Labs, IBM Bangalore Email: prasanna@in.ibm.com Ph: 91-80-25044636 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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