From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yb1-xb2c.google.com (mail-yb1-xb2c.google.com [IPv6:2607:f8b0:4864:20::b2c]) by sourceware.org (Postfix) with ESMTPS id DECFF3858C27 for ; Tue, 12 Oct 2021 16:07:37 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org DECFF3858C27 Received: by mail-yb1-xb2c.google.com with SMTP id w10so47771233ybt.4 for ; Tue, 12 Oct 2021 09:07:37 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=PT3I9VfjyXDd4M0jpvwDzdHS5153LqpZTe+9feFgw9M=; b=TeKwY0tAScwOc/FqrPE+X8XRmk0WqCEg6kW5aKNkGaZMkL9R579sDnoIG1Qz5QyVWC vFUbGAORaSPeQhhzmHZsE5NOPE2Y06jLle2OQH2P7wuUr+aMg5YZ3ZIeXZ+pAud1aCW2 rAZuvpuXA9bdMFUH/dQGCswuwzBGxq0GN724UIHxDhjTbaU8wrrM+5Xt5v0VJShNm2Dm IaZ5Ki74fAyZKi13kkIVn8PFiYWhNXM+JCBKH33b9QTkrCS3m0Ua/jHRkB2L/xG0DIOG OIEVBmtI/cDiMuD4q+XJKi397kMI44+9q7QotHQioJmR8CBjT/puwI0mpp7atkFufOC9 sDNg== X-Gm-Message-State: AOAM531jZSbs3vxGkMpEkChjfIGyqCX6wmjXyYKZcBuF/K1lHHSOJR+8 KWP7kHoa7vTpDurWtO8wnVNGDo5CZmoenQM/+skk7Q== X-Google-Smtp-Source: ABdhPJxTQ7NQ9UX5UJRft3qm0/R07kT3n1ptoR2TAXFRUruIEx8IoThyYoD2KrhQfJQjo49qgZrDDxoxK7X1pb1Ny1Y= X-Received: by 2002:a25:7383:: with SMTP id o125mr28752609ybc.525.1634054857153; Tue, 12 Oct 2021 09:07:37 -0700 (PDT) MIME-Version: 1.0 References: <20211008065740.1485737-1-maskray@google.com> <3368ef30-eb8c-8828-1af0-1a227d99dc93@suse.com> In-Reply-To: From: =?UTF-8?B?RsSBbmctcnXDrCBTw7JuZw==?= Date: Tue, 12 Oct 2021 09:07:25 -0700 Message-ID: Subject: Re: [PATCH] elf: Support DT_RELR relative relocation format [BZ #27924] To: "H.J. Lu" Cc: Jan Beulich , libc-alpha@sourceware.org, binutils@sourceware.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-17.8 required=5.0 tests=BAYES_00, DKIMWL_WL_MED, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, ENV_AND_HDR_SPF_MATCH, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, USER_IN_DEF_DKIM_WL, USER_IN_DEF_SPF_WL 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: Tue, 12 Oct 2021 16:07:42 -0000 On Tue, Oct 12, 2021 at 7:10 AM H.J. Lu wrote: > > On Tue, Oct 12, 2021 at 1:18 AM Jan Beulich via Libc-alpha > wrote: > > > > On 11.10.2021 20:43, F=C4=81ng-ru=C3=AC S=C3=B2ng wrote: > > > On Mon, Oct 11, 2021 at 12:48 AM Jan Beulich wrot= e: > > >> > > >> On 08.10.2021 08:57, Fangrui Song via Binutils wrote: > > >>> --- a/elf/dynamic-link.h > > >>> +++ b/elf/dynamic-link.h > > >>> @@ -192,6 +192,33 @@ elf_machine_lazy_rel (struct link_map *map, st= ruct r_scope_elem *scope[], > > >>> # define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Not= hing to do. */ > > >>> # endif > > >>> > > >>> +# define ELF_DYNAMIC_DO_RELR(map) = \ > > >>> + do { = \ > > >>> + ElfW(Addr) l_addr =3D (map)->l_addr, base =3D 0, start; = \ > > >>> + const ElfW(Relr) *r =3D 0, *end =3D 0; = \ > > >>> + if (!(map)->l_info[DT_RELR]) = \ > > >>> + break; = \ > > >>> + start =3D D_PTR((map), l_info[DT_RELR]); = \ > > >>> + r =3D (const ElfW(Relr) *)start; = \ > > >>> + end =3D (const ElfW(Relr) *)(start + (map)->l_info[DT_RELRSZ]-= >d_un.d_val); \ > > >>> + for (; r < end; ++r) { = \ > > >>> + ElfW(Relr) entry =3D *r; = \ > > >>> + if ((entry & 1) =3D=3D 0) { = \ > > >>> + *((ElfW(Addr) *)(l_addr + entry)) +=3D l_addr; = \ > > >>> + base =3D entry + sizeof(ElfW(Addr)); = \ > > >>> + continue; = \ > > >>> + } = \ > > >>> + ElfW(Addr) offset =3D base; = \ > > >>> + do { = \ > > >>> + entry >>=3D 1; = \ > > >>> + if ((entry & 1) !=3D 0) = \ > > >>> + *((ElfW(Addr) *)(l_addr + offset)) +=3D l_addr; = \ > > >>> + offset +=3D sizeof(ElfW(Addr)); = \ > > >>> + } while (entry !=3D 0); = \ > > >>> + base +=3D (8 * sizeof(ElfW(Relr)) - 1) * sizeof(ElfW(Addr));= \ > > >> > > >> While in line with the proposed spec additions I'm afraid the uses o= f > > >> ElfW(Addr) here aren't universally correct: You assume that ELF > > >> container type (size) expresses an aspect of the ABI. While this is > > >> indeed the case for several arch-es, I think this has been a mistake= . > > >> IA-64, while meanwhile mostly dead, is (was) an example where 64-bit > > >> code can validly live in a 32-bit ELF container (at least as far as > > >> the psABI is concerned; I have no idea whether glibc actually > > >> followed the spec). There's a separate ELF header flag indicating th= e > > >> ABI, and hence the size of a pointer. > > > > > > Thanks for chiming in. > > > > > > As of ia64 buildability, it works for me: > > > > > > scripts/build-many-glibcs.py /tmp/glibc-many compilers ia64-linux-gnu > > > mkdir -p out/ia64; cd out/ia64 > > > ../../configure --prefix=3D/tmp/glibc/ia64 --host=3Dia64-linux-gnu > > > CC=3D/tmp/glibc-many/install/compilers/ia64-linux-gnu/bin/ia64-glibc-= linux-gnu-gcc > > > CXX=3D/tmp/glibc-many/install/compilers/ia64-linux-gnu/bin/ia64-glibc= -linux-gnu-g++ > > > make -j 50 > > > > I didn't suggest the build would fail. What I said is that I don't > > think the code is correct there. > > > > > As of the actual functionality, ugh, I cannot find ia64 in my Debian > > > testing's qemu-user-static package:( So I cannot test. > > > > > > That said, gold and LLD don't support ia64. > > > If we have a concern that ia64 may not work, the GNU ld maintainers > > > can simply not add ia64 support:) > > > > But you realize that I took ia64 only as example, as that's where > > I know ABI (pointer size) and ELF container size aren't connected. > > As per my looking at merely EF_MIPS_* in context of reading > > Joseph's reply, it might be that MIPS is another such example. But > > I lack sufficient knowledge of MIPS ... > > > > The new code should be tested and verified on all supported > targets. That is another reason to implement this in binutils > ld first. --pack-dyn-relocs=3Drelr is well tested on arm, aarch64, and x86, and works on popular arches like ppc64 as well. For mips, it is no harm to keep the DT_RELR code path. Its elf_machine_rel_relative is empty and it has no relative relocation anyway. I wish that our reasonable design decisions are not restricted by the few retrocomputing architectures, especially when the concern is still at the theoretical stage. Well, if DT_RELR has issue, don't use it; nobody forces them to use DT_RELR= . After all, --pack-dyn-relocs=3Drelr is opt in. On the other side, DT_RELR is a really great addition to save code size for non-exotic architectures. Distributions will benefit a lot. LLD users can immediately benefit. gold users can considerably leverage the feature relatively easily since a patch is available.