arc: clone: Fix CLONE_THREAD detection
For thread group case (CLONE_THREAD), the cached PID of new process/thread
need not be reset. The old logic to decide that was flawed as it would be
true only for exact combination of CLONE_THREAD + _VM, but would fail for
CLONE_THREAD + _VM + _xyz.
More detailed tear-down of current and new code below.
Current implementation is:
--------------------->8--------------------
; r12 contains clone flags
mov_s r2, CLONE_THREAD_N_VM; r2 contains bit mask
and_s r2, r2, r12 ; r2 contains bit mask AND clone flags
; but r12 still contains the same flags
brne r2, r12, .Lgo_thread ; here we compare modified mask with
; flags as they were and skip pthread TID/PID
; setup if r2 != r12 which happens all
; the time except clone flags were
; exactly CLONE_THREAD | CLONE_VM
--------------------->8--------------------
New implementation is:
--------------------->8--------------------
; r12 contains clone flags
mov_s r2, CLONE_THREAD_N_VM; r2 contains bit mask
and_s r12, r12, r2 ; r12 contains clone flags AND bit mask
; i.e. we did mask all flags except
; CLONE_THREAD and CLONE_VM
breq r2, r12, .Lgo_thread ; here we compare masked flags with
; target mask and if they match we skip
; pthread TID/PID setup
--------------------->8--------------------
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
Alexey Brodkin