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 [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id CA8893857019 for ; Wed, 17 May 2023 19:30:30 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org CA8893857019 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1684351830; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=W1aLtGBJnVq02jOTTYP8QFRl8bEYXKdnvTHtSEYHDUM=; b=E2IOA+ilI1fvyC8w/q2p0+Uw/kokx1fbzELzKIHyc/7o5uNlLC8WG96Geir/vIxWqOz5lm SnC2FY7dchcamAPUqBdwcV/SqIxv7xqdtezN3I3KsSPwFqUquPUrGolM9unj3KWPp81eso jEbwpQ4BzBgNtSNvtus0PldQn5tJjSk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-304-RtkFmQmIN3CmxS9x-VCtpQ-1; Wed, 17 May 2023 15:30:26 -0400 X-MC-Unique: RtkFmQmIN3CmxS9x-VCtpQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9A4BE867959; Wed, 17 May 2023 19:30:26 +0000 (UTC) Received: from oldenburg3.str.redhat.com (unknown [10.39.192.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C32CB40C6EC4; Wed, 17 May 2023 19:30:25 +0000 (UTC) From: Florian Weimer To: Joseph Myers Cc: Subject: Re: Making a syscall before ld.so self-relocation on MIPS References: <87wn17jogh.fsf@oldenburg3.str.redhat.com> Date: Wed, 17 May 2023 21:30:24 +0200 In-Reply-To: (Joseph Myers's message of "Wed, 17 May 2023 19:01:26 +0000") Message-ID: <87jzx6hi27.fsf@oldenburg3.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: * Joseph Myers: > On Wed, 17 May 2023, Florian Weimer via Libc-alpha wrote: > >> I'm reviewing HIDDEN_VAR_NEEDS_DYNAMIC_RELOC if they support inline >> system calls (without function calls), so that I can make a system call >> (mmap actually) before initial self-relocation of the dynamic loader. >> >> So far, it looks good in theory, except on MIPS. First there is MIPS16: >> >> /* There's no MIPS16 syscall instruction, so we go through out-of-line >> standard MIPS wrappers. These do use inline snippets below though, >> through INTERNAL_SYSCALL_MIPS16. Spilling the syscall number to >> memory gives the best code in that case, avoiding the need to save >> and restore a static register. */ >> >> Is MIPS16 the default in GCC? We don't build for explicitly in >> scripts/build-many-glibcs.py. > > No, it's not the default; you need to use the -mips16 option. And apparently this is expected to work for building glibc? We have some support code for it. I guess I could override that for elf/rtld.c with -mno-mips16. Would it be okay to do that, and rely on GCC generating a direct bal instruction for invoking the system call helper? Thanks, Florian