Re: [Xen-devel] RFC: how to differentiate livepatched symbol and original symbol in Xen hypervisor

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.06.16 at 15:32, <dongli.zhang@xxxxxxxxxx> wrote:
> Hi,
> 
> About the livepatch TODO: "Make XENPF_get_symbol also include Live Patch
> symbols" mentioned at http://wiki.xenproject.org/wiki/XSplice, I am 
> wondering
> how the patched function would be dumped.
> 
> For instance, if function "gnttab_usage_print_all" is livepatched, it  would
> show as symbol in both Xen hypervisor and applied livepatch. How are we 
> going
> to differentiate the old and new symbols referring to the same symbol name 
> but
> different address? One address is the original and another is the on pointed 
> by
> instruction "e9 xxxxxxxx".
> 
> Here is a sample on my test machine. The following is my own customized xen
> debug message in "xl debug-keys x". I am patching my own function 
> "my_old_func"
> in Xen hypervisor.
> 
> (XEN) name=my_global_domain, value=0xffff82d080409054, size=28, new=1
> (XEN) name=my_old_func, value=0xffff82d080409070, size=89, new=0
> (XEN) name=mg_data, value=0xffff82d08040a000, size=4, new=1
> 
> The following is the current result of XENPF_get_symbol on Dom0:
> 
> root@vm:/soft/img# cat /proc/xen/xensyms | grep my_old_func
> ffff82d0802465a4 T my_old_func
> ffff82d0802465a4 t .text.my_old_func
> 
> In this example, I livepatched "my_old_func" and thus we have two symbols
> referring the same name but different addresses now (ffff82d0802465a4 and
> ffff82d080409070).
> 
> Are we going to use new nm symbol flag , append extra string in symbol name
> (e.g., my_old_func#livepatch) or this even does not matter?

While the output is clearly wrong, the problem isn't distinguishing
the symbols - that's simple: Everything outside of [_start,_end)
is in a livepatch. (One issue here would be multiple replacement of
the same symbol.) The main problem I see here is that
xensyms_read() doesn't even enumerate the new symbols.

Jan


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