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[173.198.77.218]) by smtp.gmail.com with ESMTPSA id u27sm3567797pfg.83.2021.08.02.11.46.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Aug 2021 11:46:26 -0700 (PDT) Subject: Re: [PATCH] target/i386: cmpxchg should not touch accumulator To: yqwfh , qemu-devel@nongnu.org References: <20210731190507.9007-1-amdeniulari@protonmail.com> From: Richard Henderson Message-ID: Date: Mon, 2 Aug 2021 08:46:22 -1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210731190507.9007-1-amdeniulari@protonmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::102a; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x102a.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniele Ahmed Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/31/21 9:06 AM, yqwfh wrote: > Signed-off-by: Daniele Ahmed > --- > target/i386/tcg/translate.c | 9 --------- > 1 file changed, 9 deletions(-) > > diff --git a/target/i386/tcg/translate.c b/target/i386/tcg/translate.c > index aacb605..41386dd 100644 > --- a/target/i386/tcg/translate.c > +++ b/target/i386/tcg/translate.c > @@ -5366,7 +5366,6 @@ static target_ulong disas_insn(DisasContext *s, CPUState *cpu) > gen_lea_modrm(env, s, modrm); > tcg_gen_atomic_cmpxchg_tl(oldv, s->A0, cmpv, newv, > s->mem_index, ot | MO_LE); > - gen_op_mov_reg_v(s, ot, R_EAX, oldv); > } else { > if (mod == 3) { > rm = (modrm & 7) | REX_B(s); > @@ -5381,15 +5380,7 @@ static target_ulong disas_insn(DisasContext *s, CPUState *cpu) > /* store value = (old == cmp ? new : old); */ > tcg_gen_movcond_tl(TCG_COND_EQ, newv, oldv, cmpv, newv, oldv); > if (mod == 3) { > - gen_op_mov_reg_v(s, ot, R_EAX, oldv); > gen_op_mov_reg_v(s, ot, rm, newv); > - } else { > - /* Perform an unconditional 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(s, ot, newv, s->A0); > - gen_op_mov_reg_v(s, ot, R_EAX, oldv); > } Obviously incorrect. You can't *not* store to EAX. You must conditionally store to EAX. r~