From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=35772 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OtLNZ-00078F-2z for qemu-devel@nongnu.org; Wed, 08 Sep 2010 10:12:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OtLNW-0005Uf-U5 for qemu-devel@nongnu.org; Wed, 08 Sep 2010 10:12:00 -0400 Received: from fe02x03-cgp.akado.ru ([77.232.31.165]:56516 helo=akado.ru) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OtLNW-0005Su-Mh for qemu-devel@nongnu.org; Wed, 08 Sep 2010 10:11:58 -0400 Date: Wed, 8 Sep 2010 18:11:50 +0400 (MSD) From: malc Subject: Re: [Qemu-devel] [PATCH] Improve cmpxchg emulation. In-Reply-To: <1283954337-28760-1-git-send-email-jakllsch@kollasch.net> Message-ID: References: <1283954337-28760-1-git-send-email-jakllsch@kollasch.net> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Jonathan A. Kollasch" Cc: qemu-devel@nongnu.org On Wed, 8 Sep 2010, Jonathan A. Kollasch wrote: > Change the accumulator only after performing the redundant write during > cmpxchg. This fixes pthreaded programs using fork() in NetBSD/i386 > guests. > > >From Andreas Gustafsson in https://bugs.launchpad.net/qemu/+bug/569760. This is tab damaged. Secondly it looks as if this addresses only a small part of a general problem [1], also in a very naive and inefficient way, while also opening a hole can of worms (should real parallel execution for TCG be ever implemented) [1] http://www.mail-archive.com/qemu-devel@nongnu.org/msg40000.html > > Signed-off-by: Jonathan A. Kollasch > --- > target-i386/translate.c | 12 ++++++++---- > 1 files changed, 8 insertions(+), 4 deletions(-) > > diff --git a/target-i386/translate.c b/target-i386/translate.c > index 7b6e3c2..391830f 100644 > --- a/target-i386/translate.c > +++ b/target-i386/translate.c > @@ -4879,20 +4879,24 @@ static target_ulong disas_insn(DisasContext *s, target_ulong pc_start) > tcg_gen_sub_tl(t2, cpu_regs[R_EAX], t0); > gen_extu(ot, t2); > tcg_gen_brcondi_tl(TCG_COND_EQ, t2, 0, label1); > + label2 = gen_new_label(); > if (mod == 3) { > - label2 = gen_new_label(); > gen_op_mov_reg_v(ot, R_EAX, t0); > tcg_gen_br(label2); > gen_set_label(label1); > gen_op_mov_reg_v(ot, rm, t1); > - gen_set_label(label2); > } else { > - tcg_gen_mov_tl(t1, t0); > + /* perform no-op store cycle like physical cpu; must be > + before changing accumulator to ensure idempotency if > + the store faults and the instruction is restarted > + */ > + gen_op_st_v(ot + s->mem_index, t0, a0); > gen_op_mov_reg_v(ot, R_EAX, t0); > + tcg_gen_br(label2); > gen_set_label(label1); > - /* always store */ > gen_op_st_v(ot + s->mem_index, t1, a0); > } > + gen_set_label(label2); > tcg_gen_mov_tl(cpu_cc_src, t0); > tcg_gen_mov_tl(cpu_cc_dst, t2); > s->cc_op = CC_OP_SUBB + ot; > -- mailto:av1474@comtv.ru