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 AD2C33858D34 for ; Sat, 31 Jul 2021 17:11:08 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org AD2C33858D34 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-325-ombWM59WMDSdr0l8mcMP5A-1; Sat, 31 Jul 2021 13:11:04 -0400 X-MC-Unique: ombWM59WMDSdr0l8mcMP5A-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7EB81801A92; Sat, 31 Jul 2021 17:11:03 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.123]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B99965D9D5; Sat, 31 Jul 2021 17:11:02 +0000 (UTC) From: Florian Weimer To: "H.J. Lu" Cc: "H.J. Lu via Libc-alpha" Subject: Re: [PATCH v2] Place ENTRY_POINT in .text.unlikely section [BZ #28153] References: <20210731151316.1659316-1-hjl.tools@gmail.com> <87o8aiv3sl.fsf@oldenburg.str.redhat.com> Date: Sat, 31 Jul 2021 19:11:01 +0200 In-Reply-To: (H. J. Lu's message of "Sat, 31 Jul 2021 10:06:54 -0700") Message-ID: <87k0l6v26y.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-12.2 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_STOCKGEN, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) 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: Sat, 31 Jul 2021 17:11:09 -0000 * H. J. Lu: > On Sat, Jul 31, 2021 at 9:36 AM Florian Weimer wrote: >> >> * H. J. Lu via Libc-alpha: >> >> > diff --git a/sysdeps/aarch64/start.S b/sysdeps/aarch64/start.S >> > index 417da8802b..e46e01ed0b 100644 >> > --- a/sysdeps/aarch64/start.S >> > +++ b/sysdeps/aarch64/start.S >> > @@ -42,7 +42,7 @@ >> > NULL >> > */ >> > >> > - .text >> > + .section .text.unlikely,"ax",%progbits >> > ENTRY(_start) >> > /* Create an initial frame with 0 LR and FP */ >> > cfi_undefined (x30) >> >> I don't think it's correct to place code that runs during every process >> start into .text.unlikely. Surely we can avoid that page fault. >> >> Can we fix the ENTRY_POINT assumption in profiling instead? > > We can do > > diff --git a/csu/gmon-start.c b/csu/gmon-start.c > index b3432885b3..83322fd586 100644 > --- a/csu/gmon-start.c > +++ b/csu/gmon-start.c > @@ -48,7 +48,7 @@ > #ifdef ENTRY_POINT_DECL > ENTRY_POINT_DECL(extern) > #else > -extern char ENTRY_POINT[]; > +extern char entry_point[] asm (__SYMBOL_PREFIX "main"); > #endif > extern char etext[]; > > @@ -56,7 +56,7 @@ extern char etext[]; > # ifdef ENTRY_POINT_DECL > # define TEXT_START ENTRY_POINT > # else > -# define TEXT_START &ENTRY_POINT > +# define TEXT_START &entry_point > # endif > #endif > > But this may only work with BFD linker which places .text.startup > section before .text section. Can we get the linker to emit a symbol at the start of the text section? Like it does for orphan sections? Then we can use a weak symbol reference in gmon-start.c and use the new symbol if it is available. Thanks, Florian