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 <[email protected]>
Acked-by: Vineet Gupta <[email protected]>
---
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
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