From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pj1-x1032.google.com (mail-pj1-x1032.google.com [IPv6:2607:f8b0:4864:20::1032]) by sourceware.org (Postfix) with ESMTPS id 32079383B805; Fri, 18 Jun 2021 00:24:38 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 32079383B805 Received: by mail-pj1-x1032.google.com with SMTP id s17-20020a17090a8811b029016e89654f93so7089061pjn.1; Thu, 17 Jun 2021 17:24:38 -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=hO8L6VGGKi24WPn9YXjh4b19ecN9XtkyoJxDkL1ZMno=; b=WVN2eubdCgV1AmOuwgeQ9BwPe1fJkp1zkrR/un4AO781pHl0QPYYg0L6rtmMTJLcxa Zt+8FxDW/Gmnw8jVTqLyjlY7fvnW3+jPSDwjQCR/RpoIp0xS6wLzwWD5Gs0C+RWWJD+9 IuwBOTSIOvuu0Lkjxwt8p0O8uts5mQPABcZ0d75IXqOX6KBZC0TleuSK5CyP6PUw4lCg awcB15Evp5OLeP6CwgBJC9FhXLv/2YCUQbLNY/z98TSnh33RDPZRY0YsnWhYTAiXQQdw gEA263XghLjCPPufrCzeGqKBvlxzu6m0JTB69DM7XBJQddmK9B7OEEy+POg7ZtImueD7 9X3g== X-Gm-Message-State: AOAM533bDkxvMQbxwoUt6sNwqzHDDmOc0/33xU8pm/VLsjXq0Dit8i3Z x7dNWYwXJKnkE4UPtBmO3I6+TYY3NMn3IyTNQxQ= X-Google-Smtp-Source: ABdhPJwXAI1uLAQ3u0FmS9Iwu7zVP+WLF0As1sLJ1dWXXBR6exE9pHiGgSUF/oYEhMLIVzOdRXFtzVQiiQEP3E8PT8g= X-Received: by 2002:a17:90b:10e:: with SMTP id p14mr1948880pjz.153.1623975877347; Thu, 17 Jun 2021 17:24:37 -0700 (PDT) MIME-Version: 1.0 References: <20210617193825.zzjyoybttajksw5x@google.com> <20210618000600.c7yh6twgbukmyouj@google.com> In-Reply-To: <20210618000600.c7yh6twgbukmyouj@google.com> From: "H.J. Lu" Date: Thu, 17 Jun 2021 17:24:01 -0700 Message-ID: Subject: Re: [llvm-dev] RFC: Add GNU_PROPERTY_UINT32_AND_XXX/GNU_PROPERTY_UINT32_OR_XXX To: =?UTF-8?B?RsSBbmctcnXDrCBTw7JuZw==?= 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=-3026.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP 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 00:24:40 -0000 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 w= rote: > >> > > > >> > > On 2021-06-17, H.J. Lu via llvm-dev wrote: > >> > > >On Thu, Jan 21, 2021 at 7:02 AM H.J. Lu wro= te: > >> > > >> > >> > > >> On Wed, Jan 13, 2021 at 9:06 AM H.J. Lu w= rote: > >> > > >> > > >> > > >> > 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 out= put > >> > > >> > pr_data field are zero, this property should be removed from = 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 obje= ct > >> > > 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 any > >> > > >> > relocatable input pr_data fields. If all bits in the the outp= ut > >> > > >> > pr_data field are zero, this property should be removed from = output. > >> > > >> > > >> > > >> > If the bit is 1, some input relocatables have the feature. I= f 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/0690d= b0a3b7e5d8a44e0271a4be54aa7/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, it'= d be > >> > > very kind of you if you can collect more use cases before generali= zing > >> > > this into a non-arch-specific GNU PROPERTY. > >> > > > >> > > The "copy relocations on protected data symbols" thing is x86 spec= ific > >> > > 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 fu= nction > >> > 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 l= onger > >> compatible with copy relocations, just make the shared object's non-we= ak > >> 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 since = 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 eve= r exists > >> // outside glibc elf/vis*.c > >> > >> I have checked all of binutils 2.11, 2.16, 2.20, 2.24, 2.35. The have > >> 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 function > >> never works with GNU ld. > >> So no compatibility concern. > >> Fixing it (https://sourceware.org/pipermail/binutils/2021-June/116985.= html) > >> doesn't need any GNU PROPERTY. > >> > >> --- > >> > >> For variables, if an object file/archive member does not have GNU PROP= ERTY, do > >> you consider it incompatible with "single global definition"? That is = why I > >> mentioned crt1.o crti.o crtbegin.o crtend.o crtn.o and libc_nonshared.= a members > >> written in assembly. > >> > >> If you consider such an object compatible with "single global definiti= on", I > >> don't see why a GNU PROPERTY is needed. > >> > >> If you consider such an object incompatible with "single global defini= tion", I > >> don't see how "single global definition" benefits can be claimed givin= g 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, t= he executable > >and its dependency shared libraries. > >=E2=80=A2 Issue an error/warning if the marker is not consistent on all = 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, the = executable and its dependency shared libraries. =E2=80=A2 Disallow copy relocation against definition with the STV_PROTECTE= D visibility in the shared library with the marker. =E2=80=A2 For systems without function descriptor: =E2=80=A2 Disallow non-GOT function pointer reference in executable without the marker to the definition with the STV_PROTECTED visibility in a shared library with the marker. =E2=80=A2 Use the address of the function body as function pointer on funct= ions with the STV_PROTECTED visibility, which are defined in shared libraries with the ma= rker. --=20 H.J.