[uclibc-ng-devel] [PATCH 2/3] 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(a)synopsys.com> Acked-by: Vineet Gupta <vgupta(a)synopsys.com> --- libc/sysdeps/linux/arc/clone.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/libc/sysdeps/linux/arc/clone.S b/libc/sysdeps/linux/arc/clone.S index dbb3fa7..fc8dfcf 100644 --- a/libc/sysdeps/linux/arc/clone.S +++ b/libc/sysdeps/linux/arc/clone.S @@ -69,8 +69,8 @@ ENTRY(clone) .Lnext_clone_quirk: #ifdef RESET_PID mov_s r2, CLONE_THREAD_N_VM - and_s r2, r2, r12 - brne r2, r12, .Lgo_thread + and_s r12, r12, r2 + breq r2, r12, .Lgo_thread mov r8, __NR_getpid ARC_TRAP_INSN ; r0 has PID -- 2.7.4