Re: [PATCH 0/7] Uprobes: Support SDT markers having reference count (semaphore)

[Ravi Bangoria]

Hi Masami,

>>> Hmm, it sounds simple... maybe we can increment refctr in install_breakpoint/
>>> remove_breakpoint?
>>
>> Not really, it would be simpler if I can put it inside install_breakpoint().
>> Consider an mmap() case. Probed instruction resides in the text section whereas
>> reference counter resides in the data section. These sections gets mapped using
>> separate mmap() calls. So, when process mmaps the text section we will change the
>> instruction, but section holding the reference counter may not have been mapped
>> yet in the virtual memory. If so, we will fail to update the reference counter.
> 
> Got it. 
> In such case, maybe we can hook the target page mmapped and do install_breakpoint()
> at that point. Since the instruction is protected by a refctr, unless mmap the
> page on where the refctr is, the program doesn't reach the tracepoint. Is that right?
> 

You mean, when mmap(text) happens, save the target page somewhere and when
mmap(data) happens, update both instruction and ref_ctr?

This sounds feasible. Let me think on it.

Thanks for suggestion,
Ravi