RE: [3/3] Userspace probes prototype-take2

["Zhang, Yanmin" <yanmin.zhang@intel.com>]

>>-----Original Message-----
>>From: Zhang, Yanmin
>>Sent: 2006年2月20日 11:16
>>To: Zhang, Yanmin; prasanna@in.ibm.com; systemtap@sources.redhat.com
>>Subject: RE: [3/3] Userspace probes prototype-take2
>>
>>I lost an important comment. The patch is not aware of signal processing. After kernel prepares the single-step-inst on the stack, if
>>a signal is delivered to the thread, kernel will save some states into stack and switch to signal handler function, so single-step-inst
>>on the stack might be erased.
>>
>>>>-----Original Message-----
>>>>From: systemtap-owner@sourceware.org [mailto:systemtap-owner@sourceware.org] On Behalf Of Zhang, Yanmin
>>>>Sent: 2006年2月17日 17:20
>>>>To: prasanna@in.ibm.com; systemtap@sources.redhat.com
>>>>Subject: RE: [3/3] Userspace probes prototype-take2
>>>>
>>>>2 main issues:
>>>>1) task switch caused by external interrupt when single-step;
[YM] I think we could resolve this problem. Kernel probe has some differences from uprobe. One of them is that we couldn't estimate if kernel probe happens in process context, or interrupt context, while uprobe always happens in process context (user space). So from some points of view, uprobe could be simplified from kernel probe.
a) Don't use kcb (kprobe_ctlblk) if uprobe is triggered. Create new functions, kprobe__handler_user, kprobe_fault_handler_user and other handlers. In the new functions, instead of kcb, we could use uprobe_page being allocated dynamically. Considering signal action handler (possible uprobe nested), a thread might have a list of uprobe_page.
b) Delete current_uprobe;



>>>>2) multi-thread:
[YM] We could resolve this problem.
a) Don't call replace_orignal_insn in function uprobe_single_step. It might cause a race condition.
b) Delete copy_insn_on_new_page;
c) Merge copy_insn_onstack and copy_insn_onexpstack. The single-step-insn address could be esp-sizeof(long long)-MAX_INSN_SIZE*sizeof(kprobe_opcode_t). 
d) If the stack couldn't be expanded, just kill the thread. It's reasonable because the stack is used up.


>>>>
>>>>See below inline comments.
>>>>
>>>>Yanmin
>>>>
>>>>>>-----Original Message-----
>>>>>>From: systemtap-owner@sourceware.org [mailto:systemtap-owner@sourceware.org] On Behalf Of Prasanna S Panchamukhi
>>>>>>Sent: 2006年2月8日 22:14
>>>>>>To: systemtap@sources.redhat.com
>>>>>>Subject: Re: [3/3] Userspace probes prototype-take2
>>>>>>
>>>>>>
>>>>>>This patch handles the executing the registered callback
>>>>>>functions when probes is hit.