From: Richard Henderson <rth@twiddle.net>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>,
qemu-devel@nongnu.org, Aurelien Jarno <aurelien@aurel32.net>
Subject: Re: [Qemu-devel] Shifts, ppc[64], xtensa
Date: Wed, 19 Sep 2012 10:00:38 -0700 [thread overview]
Message-ID: <5059FA36.1080301@twiddle.net> (raw)
In-Reply-To: <CAFEAcA8PU3Devb==WdvzSf4OmOK-ZvbCoCBx3-OZGcf6Tc5T_w@mail.gmail.com>
On 09/19/2012 05:57 AM, Peter Maydell wrote:
>> > - s->code_ptr += 16;
>> > + tcg_out32 (s, NOP);
>> > + tcg_out32 (s, NOP);
>> > + tcg_out32 (s, NOP);
>> > + tcg_out32 (s, NOP);
> Not too familiar with the PPC backend, but doesn't this mean that
> in the retranslation case we will overwrite a correct jump destination
> with these NOP words and then rewrite it again with the correct
> destination? That can cause problems with cache incoherency;
> compare the fix applied in commit c69806ab8276 for ARM.
Well, i386 certainly doesn't care about re-translation here:
/* direct jump method */
tcg_out8(s, OPC_JMP_long); /* jmp im */
s->tb_jmp_offset[args[0]] = s->code_ptr - s->code_buf;
tcg_out32(s, 0);
That creates an explicit branch to next.
And as far as the referenced change, that has to do with "real"
branches, i.e. INDEX_op_brcond et at. Which *do* need to be
protected against retranslation. But INDEX_op_goto_tb is a
different case.
r~
next prev parent reply other threads:[~2012-09-19 17:01 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-18 19:52 [Qemu-devel] Shifts, ppc[64], xtensa malc
2012-09-18 23:20 ` Max Filippov
2012-09-19 12:49 ` malc
2012-09-19 15:00 ` Max Filippov
2012-09-19 0:10 ` Richard Henderson
2012-09-19 12:46 ` malc
2012-09-19 12:57 ` Peter Maydell
2012-09-19 17:00 ` Richard Henderson [this message]
2012-09-19 17:02 ` Richard Henderson
2012-09-19 17:11 ` Peter Maydell
2012-09-19 17:30 ` Richard Henderson
2012-09-19 17:51 ` Aurelien Jarno
2012-09-19 18:01 ` Richard Henderson
2012-09-19 18:30 ` Peter Maydell
2012-09-19 18:35 ` Richard Henderson
2012-09-19 19:53 ` Richard Henderson
2012-09-19 20:05 ` Peter Maydell
2012-09-19 21:21 ` Richard Henderson
2012-09-20 0:29 ` Max Filippov
2012-09-20 14:03 ` Richard Henderson
2012-09-20 14:22 ` Max Filippov
2012-09-20 22:53 ` malc
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