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Fri, 04 Jun 2021 16:25:35 -0700 (PDT) Received: from [192.168.43.9] ([123.201.54.87]) by smtp.gmail.com with ESMTPSA id a9sm2826837pga.43.2021.06.04.16.25.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Jun 2021 16:25:34 -0700 (PDT) Subject: Re: [PATCH v11 08/46] target/mips: Add emulation of nanoMIPS 16-bit branch instructions To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Aleksandar Markovic , Filip Vidojevic , Vince Del Vecchio , Aleksandar Rikalo References: <1534789014-8310-1-git-send-email-aleksandar.markovic@rt-rk.com> <1534789014-8310-9-git-send-email-aleksandar.markovic@rt-rk.com> From: Faraz Shahbazker Message-ID: <2ed21c01-d82f-4279-810d-3272afcf1138@gmail.com> Date: Sat, 5 Jun 2021 04:55:08 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::536; envelope-from=faraz.shahbazker@gmail.com; helo=mail-pg1-x536.google.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 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, FREEMAIL_FROM=0.001, NICE_REPLY_A=-0.59, 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-Mailman-Approved-At: Fri, 04 Jun 2021 22:43:19 -0400 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: Peter Maydell , Dimitrije Nikolic , Stefan Markovic , Richard Henderson , "qemu-devel@nongnu.org Developers" , Aleksandar Markovic , faraz.shahbazker@mediatek.com, Petar Jovanovic , Paul Burton , Aurelien Jarno Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Philippe, On 5/29/21 7:50 PM, Philippe Mathieu-Daudé wrote: > On 5/29/21 3:52 PM, Philippe Mathieu-Daudé wrote: >> On Mon, Aug 20, 2018 at 8:17 PM Aleksandar Markovic >> wrote: >>> >>> From: Stefan Markovic >>> + case OPC_BPOSGE32: >>> + tcg_gen_andi_tl(t0, cpu_dspctrl, 0x3F); >>> + bcond_compute = 1; >>> + btgt = ctx->base.pc_next + insn_bytes + offset; > > I think this opcode never worked correctly. > > Per the "MIPS® Architecture Extension: nanoMIPS32 DSP Technical > Reference Manual — Revision 0.04" p. 88 "BPOSGE32C": > > "First, the offset argument is left-shifted by one bit to form > a 17-bit signed integer value." > > The caller, decode_nanomips_32_48_opc(), doesn't shift the offset: > > case NM_BPOSGE32C: > check_dsp_r3(ctx); > { > int32_t imm = extract32(ctx->opcode, 1, 13) | > extract32(ctx->opcode, 0, 1) << 13; > > gen_compute_branch_nm(ctx, OPC_BPOSGE32, 4, -1, -2, > imm); > } > break; I agree that the left-shift is missing. One must also note that the text in the nanoMIPS32 DSP manual is incorrect. This was most probably copy-pasted from the microMIPS DSP manual. The effective offset for nanoMIPS DSP is supposed to be 15-bit signed, not 17-bit. - farazS