From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:35814) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RZJi9-0000bi-IX for qemu-devel@nongnu.org; Sat, 10 Dec 2011 04:59:18 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RZJi8-0005EY-3c for qemu-devel@nongnu.org; Sat, 10 Dec 2011 04:59:17 -0500 Received: from gunk.araneus.fi ([166.84.6.82]:60242) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RZJi8-0005EQ-0y for qemu-devel@nongnu.org; Sat, 10 Dec 2011 04:59:16 -0500 From: Andreas Gustafsson Message-Id: <20111210095911.AE7BE75E5D@guava.gson.org> Date: Sat, 10 Dec 2011 11:59:11 +0200 (EET) Subject: [Qemu-devel] [PATCH] target-i386: fix cmpxchg instruction emulation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Alexander Graf When the i386 cmpxchg instruction is executed with a memory operand and the comparison result is "unequal", do the memory write before changing the accumulator instead of the other way around, because otherwise the new accumulator value will incorrectly be used in the comparison when the instruction is restarted after a page fault. This bug was originally reported on 2010-04-25 as https://bugs.launchpad.net/qemu/+bug/569760 Signed-off-by: Andreas Gustafsson --- --- translate.c.orig 2011-12-09 18:21:28.000000000 +0200 +++ translate.c 2011-12-09 18:21:24.000000000 +0200 @@ -4870,20 +4870,23 @@ static target_ulong disas_insn(DisasCont 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;