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Wed, 06 Apr 2022 09:37:07 -0700 (PDT) X-Received: by 2002:ac8:5944:0:b0:2e2:e4b:f4b6 with SMTP id 4-20020ac85944000000b002e20e4bf4b6mr8237181qtz.89.1649263027461; Wed, 06 Apr 2022 09:37:07 -0700 (PDT) Received: from treble ([2600:1700:6e32:6c00::15]) by smtp.gmail.com with ESMTPSA id t72-20020a37464b000000b0067ec1c9dcaesm10160791qka.44.2022.04.06.09.37.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Apr 2022 09:37:07 -0700 (PDT) Date: Wed, 6 Apr 2022 09:37:03 -0700 From: Josh Poimboeuf To: Peter Zijlstra Cc: Thomas Gleixner , kernel test robot , kbuild-all@lists.01.org, linux-kernel@vger.kernel.org, mbenes@suse.cz, x86@kernel.org, Steven Rostedt Subject: Re: drivers/gpu/drm/i915/i915.prelink.o: warning: objtool: __intel_wait_for_register_fw.cold()+0xce: relocation to !ENDBR: vlv_allow_gt_wake.cold+0x0 Message-ID: <20220406163703.hhet4ai7ztd7g4j4@treble> References: <202204041241.Hw855BWm-lkp@intel.com> <20220406000500.5hlaqy5zrdqsg5mg@treble> <87czhv11k1.ffs@tglx> <20220406053251.6dyfxrjmmgdwocfc@treble> <20220406074330.GD34954@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220406074330.GD34954@worktop.programming.kicks-ass.net> X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RDNS_NONE,SPF_HELO_NONE,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 06, 2022 at 09:43:30AM +0200, Peter Zijlstra wrote: > On Tue, Apr 05, 2022 at 10:32:51PM -0700, Josh Poimboeuf wrote: > > More broadly, this issue could theoretically happen in some other places > > throughout the kernel tree, since _THIS_IP_ is fundamentally unreliable > > as currently written. > > > > So we could look at making _THIS_IP_ more predictable. > > > > Inline asm would work better ("lea 0(%rip), %[rip]"), but then you need > > an arch-dependent implementation... > > Well, there's a ton of _THIS_IP_ instances all around, and it would be > unfortunate to have them grow into actual code :/ What do you mean by growing into actual code? It's still just a single instruction, as was the immediate load before. Though, you pasted this on irc: #define _THIS_IP_ ({ __label__ __here; __here: asm_volatile_goto ("":::: __here); (unsigned long)&&__here; }) which seems decent to me, though less than ideal because it grows an ENDBR. But I like its arch-independence, so yeah, LGTM. -- Josh