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Tue, 31 Oct 2023 13:06:43 -0700 (PDT) Date: Tue, 31 Oct 2023 13:06:39 -0700 From: Charlie Jenkins To: Andreas Schwab Cc: Emil Renner Berthing , linux-riscv@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Biederman , Kees Cook , Paul Walmsley , Palmer Dabbelt , Albert Ou , Samuel Holland , Nelson Chu , Emil Renner Berthing Subject: Re: [PATCH v7 1/3] riscv: Avoid unaligned access when relocating modules Message-ID: References: <20231031-module_relocations-v7-0-6f4719b64bf7@rivosinc.com> <20231031-module_relocations-v7-1-6f4719b64bf7@rivosinc.com> <878r7iiwb6.fsf@igel.home> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <878r7iiwb6.fsf@igel.home> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231031_130647_150988_05606660 X-CRM114-Status: GOOD ( 13.10 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Tue, Oct 31, 2023 at 05:35:57PM +0100, Andreas Schwab wrote: > On Okt 31 2023, Emil Renner Berthing wrote: > > >> +static int riscv_insn_rmw(void *location, u32 keep, u32 set) > >> +{ > >> + u16 *parcel = location; > >> + u32 insn = (u32)le16_to_cpu(parcel[0]) | (u32)le16_to_cpu(parcel[1]) << 16; > >> + > >> + insn &= keep; > >> + insn |= set; > >> + > >> + parcel[0] = cpu_to_le32(insn); > > > > Why cpu_to_le32(insn)? Unless I've misunderstood something downcasting unsigned > > to unsigned values in C (eg. from u32 to u16) is defined to always discard the > > most signifcant bits, so cpu_to_le16(insn) should be fine. > > cpu_to_le32(insn) can't be right here anyway, since it also swaps the > two u16 halves and would be the same as cpu_to_le16(insn >> 16) on big > endian. Yes, not sure why I did that... I will fix that up. - Charlie > > -- > Andreas Schwab, schwab@linux-m68k.org > GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1 > "And now for something completely different." _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv