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Fri, 05 Mar 2021 07:13:05 -0800 (PST) Received: from [192.168.1.11] ([71.212.131.83]) by smtp.gmail.com with ESMTPSA id gz12sm2720220pjb.33.2021.03.05.07.13.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Mar 2021 07:13:05 -0800 (PST) Subject: Re: [PATCH] tcg/aarch64: Fix constant subtraction in tcg_out_addsub2 To: Peter Maydell References: <20210228232847.322468-1-richard.henderson@linaro.org> From: Richard Henderson Message-ID: <1aa9a1c0-cf39-00ee-5837-019f67580c29@linaro.org> Date: Fri, 5 Mar 2021 07:13:02 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: 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::1034; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x1034.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: QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/5/21 3:45 AM, Peter Maydell wrote: > On Sun, 28 Feb 2021 at 23:55, Richard Henderson > wrote: >> >> An hppa guest executing >> >> 0x000000000000e05c: ldil L%10000,r4 >> 0x000000000000e060: ldo 0(r4),r4 >> 0x000000000000e064: sub r3,r4,sp >> >> produces >> >> ---- 000000000000e064 000000000000e068 >> sub2_i32 tmp0,tmp4,r3,$0x1,$0x10000,$0x0 >> >> after folding and constant propagation. Then we hit >> >> tcg-target.c.inc:640: tcg_out_insn_3401: Assertion `aimm <= 0xfff' failed. >> >> because aimm is in fact -16, but unsigned. >> >> The ((bl < 0) ^ sub) condition which negates bl is incorrect and will >> always lead to this abort. If the constant is positive, sub will make >> it negative; if the constant is negative, sub will keep it negative. >> >> Signed-off-by: Richard Henderson >> --- >> -static inline void tcg_out_addsub2(TCGContext *s, TCGType ext, TCGReg rl, >> - TCGReg rh, TCGReg al, TCGReg ah, >> - tcg_target_long bl, tcg_target_long bh, >> - bool const_bl, bool const_bh, bool sub) >> +static void tcg_out_addsub2(TCGContext *s, TCGType ext, TCGReg rl, >> + TCGReg rh, TCGReg al, TCGReg ah, >> + tcg_target_long bl, tcg_target_long bh, >> + bool const_bl, bool const_bh, bool sub) >> { >> TCGReg orig_rl = rl; >> AArch64Insn insn; > > Seems like an unrelated change ? Mm. Perhaps I should remove all of the inline markers all at once. r~ > >> @@ -1423,11 +1423,13 @@ static inline void tcg_out_addsub2(TCGContext *s, TCGType ext, TCGReg rl, >> } >> >> if (const_bl) { >> - insn = I3401_ADDSI; >> - if ((bl < 0) ^ sub) { >> - insn = I3401_SUBSI; >> + if (bl < 0) { >> bl = -bl; >> + insn = sub ? I3401_ADDSI : I3401_SUBSI; >> + } else { >> + insn = sub ? I3401_SUBSI : I3401_ADDSI; >> } >> + >> if (unlikely(al == TCG_REG_XZR)) { >> /* ??? We want to allow al to be zero for the benefit of >> negation via subtraction. However, that leaves open the >> -- >> 2.25.1 > > Otherwise > Reviewed-by: Peter Maydell > > thanks > -- PMM >