From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-x736.google.com (mail-qk1-x736.google.com [IPv6:2607:f8b0:4864:20::736]) by sourceware.org (Postfix) with ESMTPS id F3EF3383B805 for ; Fri, 18 Jun 2021 00:49:37 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org F3EF3383B805 Received: by mail-qk1-x736.google.com with SMTP id bj15so5192708qkb.11 for ; Thu, 17 Jun 2021 17:49:37 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=uuv8PQU1Ck3ZhRZ9ICrlQJtH092OEGOzyTDeOHibfJM=; b=KUXQzQUP2t4jefSOTIdGC8okcEExEm1PKrw/AdBoeTdLzKSfQvo8Q1ONlAqOEmAH3h 0XR0X/ZKNhxjVdPG3NLQy/wN7iipJStYCd5zn+hR5i50bU52Gbnd8pP2hf6nBeT5J438 K6o9/2hWtighOpeX74Uis31HoafnJxBXx5L2Tmtwlaiq1ZlGujxL7g3isUjO3gGnmywj 5Nmhs+Cgvbrn29gBzDQTFSlNB6VZhifkiXlgI/GjcBxJOwjiCBaTQoSn6evhA0ktKxVE /P45xpFOTjwOZQI+I5QfjDxmgfUEziSRkqL3oMMp0vhTCAM1tHJCU85BLdgToQAWsJmX 5vBQ== X-Gm-Message-State: AOAM530C78OqqyNn6rpt6m1deIiKk6ztH3cSgCXcDXf2++56aEPEW8gJ /IXryRZ5MnOq0mTUukgYBF/rKR2V6W7LqFMl0w48Kg== X-Google-Smtp-Source: ABdhPJwKL83jyZ7VhEyNwnuUh6AQAeA+MB8Pljy3facT9U91fQJ0BIMMQpFPBvIGwxJH1uhThpZGBVCXe9sHdt6KkY0= X-Received: by 2002:a25:e741:: with SMTP id e62mr10768683ybh.484.1623977377386; Thu, 17 Jun 2021 17:49:37 -0700 (PDT) MIME-Version: 1.0 References: <20210617193825.zzjyoybttajksw5x@google.com> <20210618000600.c7yh6twgbukmyouj@google.com> In-Reply-To: From: =?UTF-8?B?RsSBbmctcnXDrCBTw7JuZw==?= Date: Thu, 17 Jun 2021 17:49:26 -0700 Message-ID: Subject: Re: [llvm-dev] RFC: Add GNU_PROPERTY_UINT32_AND_XXX/GNU_PROPERTY_UINT32_OR_XXX To: "H.J. Lu" Cc: GNU gABI gnu-gabi , GCC Development , Binutils , GNU C Library , llvm-dev@lists.llvm.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-19.2 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=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gnu-gabi@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gnu-gabi mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 18 Jun 2021 00:49:39 -0000 On Thu, Jun 17, 2021 at 5:24 PM H.J. Lu wrote: > > On Thu, Jun 17, 2021 at 5:06 PM F=C4=81ng-ru=C3=AC S=C3=B2ng wrote: > > > > On 2021-06-17, H.J. Lu wrote: > > >On Thu, Jun 17, 2021 at 1:25 PM F=C4=81ng-ru=C3=AC S=C3=B2ng wrote: > > >> > > >> On Thu, Jun 17, 2021 at 12:46 PM H.J. Lu wrote= : > > >> > > > >> > On Thu, Jun 17, 2021 at 12:38 PM Fangrui Song = wrote: > > >> > > > > >> > > On 2021-06-17, H.J. Lu via llvm-dev wrote: > > >> > > >On Thu, Jan 21, 2021 at 7:02 AM H.J. Lu w= rote: > > >> > > >> > > >> > > >> On Wed, Jan 13, 2021 at 9:06 AM H.J. Lu = wrote: > > >> > > >> > > > >> > > >> > 1. GNU_PROPERTY_UINT32_AND_LO..GNU_PROPERTY_UINT32_AND_HI > > >> > > >> > > > >> > > >> > #define GNU_PROPERTY_UINT32_AND_LO 0xb0000000 > > >> > > >> > #define GNU_PROPERTY_UINT32_AND_HI 0xb0007fff > > >> > > >> > > > >> > > >> > A bit in the output pr_data field is set only if it is set = in all > > >> > > >> > relocatable input pr_data fields. If all bits in the the o= utput > > >> > > >> > pr_data field are zero, this property should be removed fro= m output. > > >> > > >> > > > >> > > >> > If the bit is 1, all input relocatables have the feature. = If the > > >> > > >> > bit is 0 or the property is missing, the info is unknown. > > >> > > > > >> > > How to use AND in practice? > > >> > > Are you going to add .note.gnu.property to all of crt1.o crti.o > > >> > > crtbegin.o crtend.o crtn.o and miscellaneous libc_nonshared.a ob= ject > > >> > > files written in assembly? > > >> > > > > >> > > >> > 2. GNU_PROPERTY_UINT32_OR_LO..GNU_PROPERTY_UINT32_OR_HI > > >> > > >> > > > >> > > >> > #define GNU_PROPERTY_UINT32_OR_LO 0xb0008000 > > >> > > >> > #define GNU_PROPERTY_UINT32_OR_HI 0xb000ffff > > >> > > >> > > > >> > > >> > A bit in the output pr_data field is set if it is set in an= y > > >> > > >> > relocatable input pr_data fields. If all bits in the the ou= tput > > >> > > >> > pr_data field are zero, this property should be removed fro= m output. > > >> > > >> > > > >> > > >> > If the bit is 1, some input relocatables have the feature. = If the > > >> > > >> > bit is 0 or the property is missing, the info is unknown. > > >> > > >> > > > >> > > >> > The PDF is at > > >> > > >> > > > >> > > >> > https://gitlab.com/x86-psABIs/Linux-ABI/-/wikis/uploads/069= 0db0a3b7e5d8a44e0271a4be54aa7/linux-gABI-and-or-2021-01-13.pdf > > >> > > >> > > > >> > > >> > -- > > >> > > >> > H.J. > > >> > > >> > > >> > > >> Here is the binutils patch to implement it. > > >> > > >> > > >> > > > > > >> > > >If there are no objections, I will check it in tomorrow. > > >> > > > > >> > > If the use case is just ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA, i= t'd be > > >> > > very kind of you if you can collect more use cases before genera= lizing > > >> > > this into a non-arch-specific GNU PROPERTY. > > >> > > > > >> > > The "copy relocations on protected data symbols" thing is x86 sp= ecific > > >> > > and only applies with gcc+GNU ld+glibc. > > >> > > Non-x86 architectures don't have this thing. > > >> > > gold doesn't have this thing. > > >> > > clang doesn't have this thing. > > >> > > > >> > It will be used to remove copy relocation and implement canonical = function > > >> > pointers, which will benefit protected data and function. > > >> > > >> The action items in > > >> https://gitlab.com/x86-psABIs/x86-64-ABI/-/issues/8#note_593822281 > > >> can be applied without a GNU PROPERTY. > > >> > > >> If we want to enforce the link-time check that a shared object is no= longer > > >> compatible with copy relocations, just make the shared object's non-= weak > > >> definitions protected, and add a GNU ld diagnostic like gold > > >> (https://sourceware.org/bugzilla/show_bug.cgi?id=3D19823) > > >> > > >> --- > > >> > > >> For functions, > > >> > > >> On x86-64, gcc -fpic has been using leaq addr()(%rip), %rax sinc= e at least > > >> 4.1.2 (oldest gcc I can find on godbolt): > > >> > > >> __attribute__((visibility("protected"))) > > >> void *addr() { return (void*)addr; } > > >> > > >> // a protected non-definition declaration is the same. > > >> > > >> // while asm(".protected addr") can use GOT, it is super rare if e= ver exists > > >> // outside glibc elf/vis*.c > > >> > > >> I have checked all of binutils 2.11, 2.16, 2.20, 2.24, 2.35. The hav= e > > >> the same diagnostic: > > >> > > >> relocation R_X86_64_PC32 against protected function `addr' can not > > >> be used when making a shared object > > >> > > >> I think we can assert that taking the address of a protected functio= n > > >> never works with GNU ld. > > >> So no compatibility concern. > > >> Fixing it (https://sourceware.org/pipermail/binutils/2021-June/11698= 5.html) > > >> doesn't need any GNU PROPERTY. > > >> > > >> --- > > >> > > >> For variables, if an object file/archive member does not have GNU PR= OPERTY, do > > >> you consider it incompatible with "single global definition"? That i= s why I > > >> mentioned crt1.o crti.o crtbegin.o crtend.o crtn.o and libc_nonshare= d.a members > > >> written in assembly. > > >> > > >> If you consider such an object compatible with "single global defini= tion", I > > >> don't see why a GNU PROPERTY is needed. > > >> > > >> If you consider such an object incompatible with "single global defi= nition", I > > >> don't see how "single global definition" benefits can be claimed giv= ing so many > > >> prebuilt object files without GNU PROPERTY. > > > > > >Please see the slides in > > > > > >https://gitlab.com/x86-psABIs/x86-64-ABI/-/issues/8 > > > > > >which includes > > > > > >Dynamic Linker for Single Global Definition > > >=E2=80=A2 Check the single global definition marker on all components,= the executable > > >and its dependency shared libraries. > > >=E2=80=A2 Issue an error/warning if the marker is not consistent on al= l components. > > > > This is not appealing from a compatibility point of view. > > It is common that a system has mixed shared objects: > > > > -fsingle-global-definition =3D> a.so (marker value 1) > > no -fsingle-global-definition =3D> b.so (marker value 0 or no marker) > > Issuing a warning will be annoying. > > > > I updated my proposal to > > Dynamic Linker for Single Global Definition > =E2=80=A2 Check the single global definition marker on all components, th= e executable > and its dependency shared libraries. I find that I forgot (in so many of my previous messages) to mention that the name "single global definition" may give a false impression. For example, a dynamic STV_DEFAULT STB_WEAK/STB_GLOBAL symbol defined in a shared object can still be interposed. > =E2=80=A2 Disallow copy relocation against definition with the STV_PROTEC= TED > visibility in the shared library with the marker. If this is for GNU ld x86 only, I'm fine with it:) gold and ld.lld just emit an error unconditionally. I think non-x86 GNU ld ports which never support "copy relocations on protected data symbols" may want to make the diagnostic unconditional as well. Well, while (Michael Matz and ) I think compatibility check for "copy relocations on protected data symbols" is over-engineering (and Alan/Cary think it was a mistake), if you still want to add it, it is fine for me... For Clang, I hope we will not emit such a property, because Clang never supports the "copy relocations on protected data symbols" scheme. > =E2=80=A2 For systems without function descriptor: > =E2=80=A2 Disallow non-GOT function pointer reference in executable witho= ut > the marker to the > definition with the STV_PROTECTED visibility in a shared library with > the marker. I think this can be unconditional, because the "pointer equality for STV_PROTECTED function address in -shared" case hasn't been working for GNU ld for at least 20 years... Many ports don't even produce a dynamic relocation. I don't mind if you add it just for symmetry, but it just feels unneeded. > =E2=80=A2 Use the address of the function body as function pointer on fun= ctions with the > STV_PROTECTED visibility, which are defined in shared libraries with the = marker. > > -- > H.J.