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=-3.4 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL,SPF_PASS autolearn=ham autolearn_force=no version=3.4.2 Received: (qmail 24010 invoked from network); 30 Apr 2020 03:42:00 -0000 Received-SPF: pass (mother.openwall.net: domain of lists.openwall.com designates 195.42.179.200 as permitted sender) receiver=inbox.vuxu.org; client-ip=195.42.179.200 envelope-from= Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 30 Apr 2020 03:42:00 -0000 Received: (qmail 25654 invoked by uid 550); 30 Apr 2020 03:41:57 -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 13412 invoked from network); 30 Apr 2020 02:51:54 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1588215102; bh=zYCedQsDI7/f6GhtRXQr5lxXl5m1nAJL1n3c6FIyzMc=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=gxFMfB5XVsdKXJjjOHPJxhhaN0oy59FHzCuao5n5C4Fz0BRqcWBG4k/0Tp6FgkJp0 Sh3MDsSLFM1hX1iLRLjQQActfnUfrlHJXGv4PdvG5lM0Y0wnhE1lPIF5ik6fa2i6ZY FJd8W3rX+terUiy1YVeIebfdlWUha5HuHNzSQpM76J4b47bkOo4N1DDTydOVPaXnCg 5CYBkiyvfcl/Is/2zhpmLlM0t5kF2s5e76m5EivM7TlXYMVFd8qaN/dilXS9gbVbx/ p4fWTwqVcl6Zek1XgTC3vY81fNEqX3K2nXgl8RKBnDbopA8c9vp215x5yhx7f2bi45 j31IM6smW2qgA== From: Michael Ellerman To: Rich Felker , Nicholas Piggin Cc: libc-alpha@sourceware.org, Andy Lutomirski , musl@lists.openwall.com, binutils@sourceware.org, Adhemerval Zanella , libc-dev@lists.llvm.org, Thomas Gleixner , Vincenzo Frascino , linuxppc-dev@lists.ozlabs.org In-Reply-To: <20200425162204.GJ11469@brightrain.aerifal.cx> References: <1587790194.w180xsw5be.astroid@bobo.none> <9371cac5-20bb-0552-2609-0d537f41fecd@c-s.fr> <1587810370.tg8ym9yjpc.astroid@bobo.none> <20200425162204.GJ11469@brightrain.aerifal.cx> Date: Thu, 30 Apr 2020 12:51:56 +1000 Message-ID: <87v9lheldf.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [musl] Re: New powerpc vdso calling convention Rich Felker writes: > On Sat, Apr 25, 2020 at 08:56:54PM +1000, Nicholas Piggin wrote: >> >> The ELF v2 ABI convention would suit it well, because the caller already >> >> 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 middle.. >> >> 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. >> >> The vdso doesn't have TOC, it has one global address (the vdso data >> page) which it loads by calculating its own address. > > A function descriptor could be put in the VDSO data page, or as it's > done now by glibc the vdso linkage code could create it. My leaning is > to at least have a version of the code that's callable (with the right > descriptor around it) by v1 binaries, but since musl does not use > ELFv1 at all we really have no stake in this and I'm fine with > whatever outcome users of v1 decide on. > >> 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: > > I'm pretty sure it does know because signal invocation has to know > whether the function pointer points to a descriptor or code. At least > for FDPIC archs (similar to PPC64 ELFv1 function descriptors) it knows > and has to know. It does know, see TIF_ELF2ABI which is tested by is_elf2_task(), and as you say is used by the signal delivery code. Currently the VDSO entry points are not functions, so they don't need to change based on the ABI. cheers