From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.1 required=5.0 tests=DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FROM,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.2 Received: (qmail 11094 invoked from network); 25 Apr 2020 23:02:11 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with UTF8ESMTPZ; 25 Apr 2020 23:02:11 -0000 Received: (qmail 28148 invoked by uid 550); 25 Apr 2020 23:02:08 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 28112 invoked from network); 25 Apr 2020 23:02:07 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:subject:to:cc:references:in-reply-to:mime-version :message-id:content-transfer-encoding; bh=kuyGG2WrwcRLhDmmOafr5C39I+M2elt9RC63O0/Z7SE=; b=EXU1uMLfZlRxtmAcs2eld6Bu7fbwGqBzOi/x2jpL7aK28iLIEgcDvgDm0LkzSkXDai VydlqHCX5agITQBVertFGGhJVWhkf4W9JdFRqYXBGapjwDvNKrWBSX8uX1+u1oAMi57q iwIBzJzvU81S3x8sZx6IiVG9Nd+8oouN7asvSdnE/JLoHDJSTNRxYCCLpmMbE2HduqPk 3WgsZ9WzhopEVQgSeOCq4RaKf0+9GNG2zIwOoC3HaIPFXXS8sW8hYwCoQHLmsgqawZVp 1hFVvqDxh7HgDt3cU+JvAYRaSdAKWKy/pZCaoifUFP5+7ZqUzKIkD5Q8qYj4sbsbdlTD YE7Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:subject:to:cc:references:in-reply-to :mime-version:message-id:content-transfer-encoding; bh=kuyGG2WrwcRLhDmmOafr5C39I+M2elt9RC63O0/Z7SE=; b=nEGrmgW9yAyzQWEO/8E3ETilsP5mfNAmWuwuXJFLiQnuRqh0pAB/TqYbFGNZ3Qiwao rbTNtHR0hn0iMRxs1/gUM63S++9XUBZJecibnDVFyDFv9yN4Y6gJn74Pi8dR2t8HS7jV fxd2m6s6jYz7jYyqMDUhiXx2kiQzNWz8YEWo4DOnpKFRuTQ5K0IUx4p+7pXurTKr/xNa 6EAdfrW56t+xRJyk99vXnAuNjUlZd/X3NTVBSB8MXZ1XBLE//scLn9w1rvDfafJRB/Bw Yyay6FXWZC8bSmQLhkUR3R2pLpEmxgHYL19QGaDg40wbICPMFj05vgqoQ6sAA5MibYu1 LC9A== X-Gm-Message-State: AGi0PuYuwtYFSjD2XgjeKwz/icbr+hccWpdvJnfO+cY0mVVhxPaODDW6 evYmj43367VKL/JZDFCbWmY= X-Google-Smtp-Source: APiQypIQz62BPXqy7A7XX0WODMxDjN3Uen5QDKuSmelR0+WXUJlbHIBrMkspB3YMzRDc1lKIJYYJRw== X-Received: by 2002:a17:90a:690b:: with SMTP id r11mr4063564pjj.119.1587855714892; Sat, 25 Apr 2020 16:01:54 -0700 (PDT) Date: Sun, 26 Apr 2020 08:58:19 +1000 From: Nicholas Piggin To: binutils@sourceware.org, Christophe Leroy , linuxppc-dev@lists.ozlabs.org Cc: Adhemerval Zanella , Rich Felker , libc-alpha@sourceware.org, libc-dev@lists.llvm.org, Andy Lutomirski , musl@lists.openwall.com, Thomas Gleixner , Vincenzo Frascino References: <1587790194.w180xsw5be.astroid@bobo.none> <9371cac5-20bb-0552-2609-0d537f41fecd@c-s.fr> <1587810370.tg8ym9yjpc.astroid@bobo.none> <976551e8-229e-54c1-8fb2-c5df94b979c3@c-s.fr> In-Reply-To: <976551e8-229e-54c1-8fb2-c5df94b979c3@c-s.fr> MIME-Version: 1.0 Message-Id: <1587855423.jug0f1n0b8.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: [musl] Re: New powerpc vdso calling convention Excerpts from Christophe Leroy's message of April 25, 2020 10:20 pm: >=20 >=20 > Le 25/04/2020 =C3=A0 12:56, Nicholas Piggin a =C3=A9crit=C2=A0: >> Excerpts from Christophe Leroy's message of April 25, 2020 5:47 pm: >>> >>> >>> Le 25/04/2020 =C3=A0 07:22, Nicholas Piggin a =C3=A9crit=C2=A0: >>>> As noted in the 'scv' thread, powerpc's vdso calling convention does n= ot >>>> match the C ELF ABI calling convention (or the proposed scv convention= ). >>>> I think we could implement a new ABI by basically duplicating function >>>> entry points with different names. >>> >>> I think doing this is a real good idea. >>> >>> I've been working at porting powerpc VDSO to the GENERIC C VDSO, and th= e >>> main pitfall has been that our vdso calling convention is not compatibl= e >>> with C calling convention, so we have go through an ASM entry/exit. >>> >>> See https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=3D17= 1469 >>> >>> We should kill this error flag return through CR[SO] and get it the >>> "modern" way like other architectectures implementing the C VDSO: retur= n >>> 0 when successfull, return -err when failed. >>=20 >> Agreed. >>=20 >>>> The ELF v2 ABI convention would suit it well, because the caller alrea= dy >>>> requires the function address for ctr, so having it in r12 will >>>> eliminate the need for address calculation, which suits the vdso data >>>> page access. >>>> >>>> Is there a need for ELF v1 specific calls as well, or could those just= be >>>> deprecated and remain on existing functions or required to use the ELF >>>> v2 calls using asm wrappers? >>> >>> What's ELF v1 and ELF v2 ? Is ELF v1 what PPC32 uses ? If so, I'd say >>> yes, it would be good to have it to avoid going through ASM in the midd= le. >>=20 >> I'm not sure about PPC32. On PPC64, ELFv2 functions must be called with >> their address in r12 if called at their global entry point. ELFv1 have a >> function descriptor with call address and TOC in it, caller has to load >> the TOC if it's global. >>=20 >> The vdso doesn't have TOC, it has one global address (the vdso data >> page) which it loads by calculating its own address. >>=20 >> The kernel doesn't change the vdso based on whether it's called by a v1 >> or v2 userspace (it doesn't really know itself and would have to export >> different functions). glibc has a hack to create something: >>=20 >> # define VDSO_IFUNC_RET(value) \ >> ({ \ >> static Elf64_FuncDesc vdso_opd =3D { .fd_toc =3D ~0x0 }; \ >> vdso_opd.fd_func =3D (Elf64_Addr)value; \ >> &vdso_opd; \ >> }) >>=20 >> If we could make something which links more like any other dso with >> ELFv1, that would be good. Otherwise I think v2 is preferable so it >> doesn't have to calculate its own address. >=20 > I see the following in glibc. So looks like PPC32 is like PPC64 elfv1.=20 > By the way, they are talking about something not completely finished in=20 > the kernel. Can we finish it ? Possibly can. It seems like a good idea to fix all loose ends if we are=20 going to add new versions. Will have to check with the toolchain people=20 to make sure we're doing the right thing. Thanks, Nick