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Tue, 4 Feb 2025 09:28:19 +0100 (CET) From: Andreas Schwab To: Jessica Clarke Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] riscv/futex: sign extend compare value in atomic cmpxchg In-Reply-To: (Jessica Clarke's message of "Mon, 3 Feb 2025 21:25:00 +0000") References: Date: Tue, 04 Feb 2025 09:28:19 +0100 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Spamd-Result: default: False [14.38 / 50.00]; SPAM_FLAG(5.00)[]; NEURAL_SPAM_LONG(3.50)[1.000]; BAYES_HAM(-3.00)[100.00%]; HFILTER_HOSTNAME_UNKNOWN(2.50)[]; NEURAL_SPAM_SHORT(2.09)[0.696]; RDNS_NONE(2.00)[]; ONCE_RECEIVED(1.20)[]; HFILTER_HELO_IP_A(1.00)[hawking.nue2.suse.org]; HFILTER_HELO_NORES_A_OR_MX(0.30)[hawking.nue2.suse.org]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_GOOD(-0.10)[text/plain]; RCVD_NO_TLS_LAST(0.10)[]; MX_GOOD(-0.01)[]; FROM_EQ_ENVFROM(0.00)[]; DIRECT_TO_MX(0.00)[Gnus/5.13 (Gnus v5.13)]; ARC_NA(0.00)[]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCPT_COUNT_THREE(0.00)[3]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCVD_COUNT_ONE(0.00)[1]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,suse.de:mid,suse.de:email] X-Spam-Flag: YES X-Spam-Score: 14.38 X-Rspamd-Queue-Id: AB8C021102 X-Rspamd-Action: add header X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spamd-Bar: ++++++++++++++ X-Spam-Level: ************** X-Spam: Yes On Feb 03 2025, Jessica Clarke wrote: > On 3 Feb 2025, at 10:06, Andreas Schwab wrote: >> >> Make sure the compare value in the lr/sc loop is sign extended to match >> what lr.w does. Fortunately, due to the compiler keeping the register >> contents sign extended anyway the lack of the explicit extension didn't >> result in wrong code so far, but this cannot be relied upon. > > GCC may guarantee this today, It doesn't, that's the point! -- Andreas Schwab, SUSE Labs, schwab@suse.de GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7 "And now for something completely different."