From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS3215 2.6.0.0/16 X-Spam-Status: No, score=-4.2 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [IPv6:2620:52:3:1:0:246e:9693:128c]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id E77FF1F8C6 for ; Sat, 31 Jul 2021 17:11:28 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 2EF28385C40C for ; Sat, 31 Jul 2021 17:11:28 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 2EF28385C40C DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1627751488; bh=Ev0zDua0NFjCDo0AzBF+NZBsCvut05p50F1ErRtof7Q=; h=To:Subject:References:Date:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=TvUg9mB8D9FlCRLLmr9exHOytFEi9ZAvTslZXTn/8ODY19n4Jn9rdUhR/wL/7r9A5 oZmuuePoWnT/O82RJd/jewCcb+8tQab2IjZjdMIQKaalDX9yjIFeoaPFemJbDVO5al GJ156xBtclhPKQYAthk8Jv59ZoHkyPRtQ3B3lHDM= 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) To: "H.J. Lu" 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-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: , From: Florian Weimer via Libc-alpha Reply-To: Florian Weimer Cc: "H.J. Lu via Libc-alpha" Errors-To: libc-alpha-bounces+e=80x24.org@sourceware.org Sender: "Libc-alpha" * 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