From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id A30E43851C2E for ; Mon, 28 Sep 2020 13:08:43 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org A30E43851C2E Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-243-HVTtF0-QPi-BIAeYTU2fYQ-1; Mon, 28 Sep 2020 09:08:38 -0400 X-MC-Unique: HVTtF0-QPi-BIAeYTU2fYQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DB77C10219E2; Mon, 28 Sep 2020 13:08:37 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-114-84.ams2.redhat.com [10.36.114.84]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 299617882A; Mon, 28 Sep 2020 13:08:37 +0000 (UTC) From: Florian Weimer To: "H.J. Lu via Libc-alpha" Subject: Re: [PATCH 1/4] x86: Initialize CPU info via IFUNC relocation [BZ 26203] References: <20200918160709.949608-1-hjl.tools@gmail.com> <20200918160709.949608-2-hjl.tools@gmail.com> Date: Mon, 28 Sep 2020 15:08:35 +0200 In-Reply-To: <20200918160709.949608-2-hjl.tools@gmail.com> (H. J. Lu via Libc-alpha's message of "Fri, 18 Sep 2020 09:07:06 -0700") Message-ID: <87imby6obw.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-11.0 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H5, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP, URIBL_BLACK autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 28 Sep 2020 13:08:45 -0000 * H. J. Lu via Libc-alpha: > X86 CPU features in ld.so are initialized by init_cpu_features, which is > invoked by DL_PLATFORM_INIT from _dl_sysdep_start. But when ld.so is > loaded by static executable, DL_PLATFORM_INIT is never called. Also > x86 cache info in libc.o and libc.a is initialized by a constructor > which may be called too late. Since _rtld_global_ro in ld.so is > initialized by dynamic relocation, we can also initialize x86 CPU > features in _rtld_global_ro in ld.so and cache info in libc.so by > initializing dummy function pointers in ld.so and libc.so via IFUNC > relocation. _rtld_global_ro is *partially* initialized by relocation. Most of it is not initialized (see the need for rtld_active). Please make this a little bit clearer in the commit message. > diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h > index 0f08079e48..5e22e795cc 100644 > --- a/sysdeps/i386/dl-machine.h > +++ b/sysdeps/i386/dl-machine.h > @@ -25,7 +25,6 @@ > #include > #include > #include > -#include > > /* Return nonzero iff ELF header is compatible with the running host. */ > static inline int __attribute__ ((unused)) > @@ -250,7 +249,7 @@ dl_platform_init (void) > #if IS_IN (rtld) > /* init_cpu_features has been called early from __libc_start_main in > static executable. */ > - init_cpu_features (&GLRO(dl_x86_cpu_features)); > + _dl_x86_init_cpu_features (); Is the commented outdated? > diff --git a/sysdeps/x86/cacheinfo.c b/sysdeps/x86/cacheinfo.c > index 217c21c34f..7a325ab70e 100644 > --- a/sysdeps/x86/cacheinfo.c > +++ b/sysdeps/x86/cacheinfo.c > + assert (cpu_features->basic.kind != arch_kind_unknown); Why doesn't this assert fire occasionally? How do you ensure that relocation processing is correctly ordered? > +/* NB: Call init_cacheinfo by initializing a dummy function pointer via > + IFUNC relocation. */ > +extern void __x86_cacheinfo (void) attribute_hidden; > +const void (*__x86_cacheinfo_p) (void) attribute_hidden > + = __x86_cacheinfo; > + > +__ifunc (__x86_cacheinfo, __x86_cacheinfo, NULL, void, init_cacheinfo); > #endif Please expand the comment and mention that is used to initialize the dormant copy of ld.so after static dlopen. The comment in sysdeps/x86/dl-get-cpu-features.c is good. > diff --git a/sysdeps/x86/dl-get-cpu-features.c b/sysdeps/x86/dl-get-cpu-features.c > index 5f9e46b0c6..da4697b895 100644 > --- a/sysdeps/x86/dl-get-cpu-features.c > +++ b/sysdeps/x86/dl-get-cpu-features.c > @@ -1,4 +1,4 @@ > -/* This file is part of the GNU C Library. > +/* Initialize CPU feature data via IFUNC relocation. > Copyright (C) 2015-2020 Free Software Foundation, Inc. > > The GNU C Library is free software; you can redistribute it and/or > @@ -18,6 +18,29 @@ > > #include > > +#ifdef SHARED > +# include > + > +/* NB: Normally, DL_PLATFORM_INIT calls init_cpu_features to initialize > + CPU features. But when loading ld.so inside of static executable, > + DL_PLATFORM_INIT isn't called. Call init_cpu_features by initializing > + a dummy function pointer via IFUNC relocation for ld.so. */ > +extern void __x86_cpu_features (void) attribute_hidden; > +const void (*__x86_cpu_features_p) (void) attribute_hidden > + = __x86_cpu_features; > + > +void > +_dl_x86_init_cpu_features (void) > +{ > + struct cpu_features *cpu_features = __get_cpu_features (); > + if (cpu_features->basic.kind == arch_kind_unknown) > + init_cpu_features (cpu_features); > +} > + > +__ifunc (__x86_cpu_features, __x86_cpu_features, NULL, void, > + _dl_x86_init_cpu_features); > +#endif > + > #undef __x86_get_cpu_features Why do we need both the conditional check and the function pointer hack? I expect that one of the function pointers can go, probably the one here. The cache hierarchy data might be used by a string function that has not been selected by IFUNC. Thanks, Florian -- Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn, Commercial register: Amtsgericht Muenchen, HRB 153243, Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill