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[2403:580b:97e8:0:321:6fb2:58f1:a1b1]) by smtp.gmail.com with ESMTPSA id q12-20020a656a8c000000b00553dcfc2179sm4264606pgu.52.2023.09.10.23.46.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 10 Sep 2023 23:46:29 -0700 (PDT) From: Alistair Francis X-Google-Original-From: Alistair Francis To: qemu-devel@nongnu.org Cc: alistair23@gmail.com, Nikita Shubin , Alistair Francis Subject: [PULL v2 45/45] target/riscv: don't read CSR in riscv_csrrw_do64 Date: Mon, 11 Sep 2023 16:43:20 +1000 Message-ID: <20230911064320.939791-46-alistair.francis@wdc.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230911064320.939791-1-alistair.francis@wdc.com> References: <20230911064320.939791-1-alistair.francis@wdc.com> MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::a2b; envelope-from=alistair23@gmail.com; helo=mail-vk1-xa2b.google.com X-Spam_score_int: -17 X-Spam_score: -1.8 X-Spam_bar: - X-Spam_report: (-1.8 / 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_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Nikita Shubin As per ISA: "For CSRRWI, if rd=x0, then the instruction shall not read the CSR and shall not cause any of the side effects that might occur on a CSR read." trans_csrrwi() and trans_csrrw() call do_csrw() if rd=x0, do_csrw() calls riscv_csrrw_do64(), via helper_csrw() passing NULL as *ret_value. Signed-off-by: Nikita Shubin Reviewed-by: Alistair Francis Message-ID: <20230808090914.17634-1-nikita.shubin@maquefel.me> Signed-off-by: Alistair Francis --- target/riscv/csr.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-) diff --git a/target/riscv/csr.c b/target/riscv/csr.c index 68eecc3c96..85a31dc420 100644 --- a/target/riscv/csr.c +++ b/target/riscv/csr.c @@ -3917,21 +3917,27 @@ static RISCVException riscv_csrrw_do64(CPURISCVState *env, int csrno, target_ulong write_mask) { RISCVException ret; - target_ulong old_value; + target_ulong old_value = 0; /* execute combined read/write operation if it exists */ if (csr_ops[csrno].op) { return csr_ops[csrno].op(env, csrno, ret_value, new_value, write_mask); } - /* if no accessor exists then return failure */ - if (!csr_ops[csrno].read) { - return RISCV_EXCP_ILLEGAL_INST; - } - /* read old value */ - ret = csr_ops[csrno].read(env, csrno, &old_value); - if (ret != RISCV_EXCP_NONE) { - return ret; + /* + * ret_value == NULL means that rd=x0 and we're coming from helper_csrw() + * and we can't throw side effects caused by CSR reads. + */ + if (ret_value) { + /* if no accessor exists then return failure */ + if (!csr_ops[csrno].read) { + return RISCV_EXCP_ILLEGAL_INST; + } + /* read old value */ + ret = csr_ops[csrno].read(env, csrno, &old_value); + if (ret != RISCV_EXCP_NONE) { + return ret; + } } /* write value if writable and write mask set, otherwise drop writes */