On 09/17/2012 06:02 PM, David Laight wrote:
/* N.B. the only way to get here is from the beq following ret_from_except. */
resume_kernel:
- /* check current_thread_info->preempt_count */
+ /* check current_thread_info, _TIF_EMULATE_STACK_STORE */
CURRENT_THREAD_INFO(r9, r1)
+ lwz r8,TI_FLAGS(r9)
+ andis. r8,r8,_TIF_EMULATE_STACK_STORE@h
+ beq+ 1f
...
+1:
Does this add a statically mispredicted branch to every
return to userspace ?
Return usersapce? No, this is just follow 'resume_kernel'.
Note I add this 'unlikely' here since I assume often Kprobe is always disabled
by default and especially its also rare to kprobe 'stwu' in many kprobe cases.
Tiejun
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