From: Chris Metcalf <cmetcalf@mellanox.com>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>,
<libc-alpha@sourceware.org>
Subject: Re: [PATCH v4] Fix clone (CLONE_VM) pid/tid reset (BZ#19957)
Date: Thu, 28 Apr 2016 20:07:00 -0000 [thread overview]
Message-ID: <19330067-0379-c612-330c-e1d569097b3b@mellanox.com> (raw)
In-Reply-To: <1461685391-5669-1-git-send-email-adhemerval.zanella@linaro.org>
On 4/26/2016 11:43 AM, Adhemerval Zanella wrote:
> --- a/sysdeps/unix/sysv/linux/tile/clone.S
> +++ b/sysdeps/unix/sysv/linux/tile/clone.S
> @@ -164,43 +164,31 @@ ENTRY (__clone)
> cfi_def_cfa_offset (FRAME_SIZE)
> cfi_undefined (lr)
> /* Check and see if we need to reset the PID, which we do if
> - CLONE_THREAD isn't set, i.e. we're not staying in the thread group.
> - If CLONE_VM is set, we're doing some kind of thread-like clone,
> - so we set the tid/pid to -1 to disable using the cached values
> - in getpid(). Otherwise (if CLONE_VM isn't set), it's a
> + CLONE_VM isn't set, i.e. we're do not share the same pthread_t
> + with parent. Otherwise (if CLONE_VM isn't set), it's a
> fork-like clone, and we go ahead and write the cached values
> from the true system pid (retrieved via __NR_getpid syscall). */
I'd change this to:
/* Check and see if we need to reset the PID, which we do if
CLONE_VM isn't set, i.e. it's a fork-like clone with a new
address space. In that case we update the cached values
from the true system pid (retrieved via __NR_getpid syscall). */
> #ifdef __tilegx__
> {
> moveli r0, hw1_last(CLONE_VM)
> - moveli r1, hw1_last(CLONE_THREAD)
> }
> {
> shl16insli r0, r0, hw0(CLONE_VM)
> - shl16insli r1, r1, hw0(CLONE_THREAD)
> }
> #else
> {
> moveli r0, lo16(CLONE_VM)
> - moveli r1, lo16(CLONE_THREAD)
> }
> {
> auli r0, r0, ha16(CLONE_VM)
> - auli r1, r1, ha16(CLONE_THREAD)
> }
> #endif
> {
> and r0, r30, r0
> - and r1, r30, r1
> - }
> - BNEZ r1, .Lno_reset_pid /* CLONE_THREAD is set */
> - {
> - movei r0, -1
> - BNEZ r0, .Lgotpid /* CLONE_VM is set */
> }
Here you have left the "{ }" around some single instructions. Stylistically,
we typically don't do that. Also, we only used the two-instruction format
for loading up r0/r1 because CLONE_THREAD needed it; CLONE_VM doesn't,
so we can collapse all the quoted code above down to just:
moveli r0, CLONE_VM
and r0, r30, r0
We could do this in one instruction if we had the bit position (i.e. log-2) of
CLONE_VM, but the obfuscation is not worth it on this not very hot path.
> + BNEZ r0, .Lno_reset_pid /* CLONE_VM is set */
> moveli TREG_SYSCALL_NR_NAME, __NR_getpid
> swint1
> -.Lgotpid:
> ADDLI_PTR r2, tp, PID_OFFSET
> {
> ST4 r2, r0
With those changes, looks good to me.
--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com
next prev parent reply other threads:[~2016-04-28 20:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-26 15:43 Adhemerval Zanella
2016-04-28 20:07 ` Chris Metcalf [this message]
2016-04-28 21:00 ` Adhemerval Zanella
2016-04-28 20:19 ` Carlos O'Donell
2016-04-28 21:04 ` Adhemerval Zanella
2016-04-29 14:06 ` Carlos O'Donell
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