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McKenney" , Boqun Feng , Will Deacon , Dave Watson , Paul Turner , Rich Felker , linux-kernel , linux-api Message-ID: <634912958.3582.1560520744040.JavaMail.zimbra@efficios.com> In-Reply-To: <87ef3wtgs4.fsf@oldenburg2.str.redhat.com> References: <20190503184219.19266-1-mathieu.desnoyers@efficios.com> <87d0jguxdk.fsf@oldenburg2.str.redhat.com> <1779359826.3226.1560518318701.JavaMail.zimbra@efficios.com> <87wohoti47.fsf@oldenburg2.str.redhat.com> <189377747.3315.1560519247118.JavaMail.zimbra@efficios.com> <87imt8tha5.fsf@oldenburg2.str.redhat.com> <26171199.3391.1560520033825.JavaMail.zimbra@efficios.com> <87ef3wtgs4.fsf@oldenburg2.str.redhat.com> Subject: Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.12_GA_3803 (ZimbraWebClient - FF67 (Linux)/8.8.12_GA_3794) Thread-Topic: glibc: Perform rseq(2) registration at C startup and thread creation (v10) Thread-Index: bTcDxImi7N70vGPu1EOcYFTLIBF+3A== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jun 14, 2019, at 3:53 PM, Florian Weimer fweimer@redhat.com wrote: > * Mathieu Desnoyers: > >> ----- On Jun 14, 2019, at 3:42 PM, Florian Weimer fweimer@redhat.com wrote: >> >>> * Mathieu Desnoyers: >>> >>>> + /* Publicize rseq registration ownership. This must be performed >>>> + after rtld re-relocation, before invoking constructors of >>>> + preloaded libraries. */ >>>> + rseq_init (); >>> >>> Please add a comment that IFUNC resolvers do not see the initialized >>> value. I think this is okay because we currently do not support access >>> to extern variables in IFUNC resolvers. >> >> Do IFUNC resolvers happen to observe the __rseq_handled address that >> was internal to ld.so ? > > They should observe the correct address, but they can access the > variable before initialization. An initializer in ld.so will not have > an effect if an interposed definition initalized the variable to > something else. > >> If so, we could simply initialize __rseq_handled twice: early before calling >> IFUNC resolvers, and after ld.so re-relocation. > > No, I don't think this will make a difference. So comment it is: /* Publicize rseq registration ownership. This must be performed after rtld re-relocation, before invoking constructors of preloaded libraries. IFUNC resolvers are called before this initialization, so they may not observe the initialized state. */ rseq_init (); Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com