From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pj1-x102f.google.com (mail-pj1-x102f.google.com [IPv6:2607:f8b0:4864:20::102f]) by sourceware.org (Postfix) with ESMTPS id 0BADA3858D35 for ; Thu, 25 Nov 2021 17:55:36 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 0BADA3858D35 Received: by mail-pj1-x102f.google.com with SMTP id j6-20020a17090a588600b001a78a5ce46aso8290971pji.0 for ; Thu, 25 Nov 2021 09:55:35 -0800 (PST) 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; bh=AK20EcARjoq0ipcU89Cxdr8dB0uj8HiydIutFuyUczc=; b=wrs+hdKwWfEejaSjAc6M6FoBWoQormranwGiuEVWP57G8fJ4KYguCa4Y/2HYqvtELo AMJ6imi9hweHDVyq4cvY7XzcSCexkIkKypEddAvY63rVkleuDd4+UTJ4GS8QG533fIxy nUwMxT7gnnKEVPcpa73pUGnkLDQPgQG+yxfbhduVu3ty2/6lXXHjoyQlOIkAxMa8plaN e86nRTnhUxl9uZoX3xDwbdAenQdvvJpl9LhThM4W6q32kw/OQvsYdC1XzoI2jbEzvjTg Og78pllUT24n6gS+Idu3JZCU5AZiHpIdQ9knW6/822sKQsHKnUxeL06zy2rf9b9EeZGW +zOg== X-Gm-Message-State: AOAM530+5eZc7fi1xE266uDI8KjU9wdRtZ5eGqPjhCOX8eOHlnFFD3F5 FQOtL3s1Lz/gb3AyXD+6aDYZu2QiFRTy6a+AF/3JtcBe X-Google-Smtp-Source: ABdhPJxMc8EYJV3D10KasFkUQfDKtcJFLOaeyxmC2m07VFJcSZ3y6un1VTP+8/SD4RZfEkcaL44JFiETH7oQC27WWgE= X-Received: by 2002:a17:90b:3a85:: with SMTP id om5mr9519964pjb.28.1637862934892; Thu, 25 Nov 2021 09:55:34 -0800 (PST) MIME-Version: 1.0 References: <20210923020207.1414230-1-hjl.tools@gmail.com> In-Reply-To: From: "H.J. Lu" Date: Thu, 25 Nov 2021 09:54:59 -0800 Message-ID: Subject: PING^3 [PATCH v4 0/2] Implement indirect external access To: GCC Patches Cc: Florian Weimer , Uros Bizjak , Jakub Jelinek , Richard Biener , Jeff Law , Adhemerval Zanella Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3022.9 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, KAM_SHORT, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP 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: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 25 Nov 2021 17:55:37 -0000 On Mon, Nov 1, 2021 at 7:02 AM H.J. Lu wrote: > > On Thu, Oct 21, 2021 at 12:56 PM H.J. Lu wrote: > > > > On Wed, Sep 22, 2021 at 7:02 PM H.J. Lu wrote: > > > > > > Changes in the v4 patch. > > > > > > 1. Add nodirect_extern_access attribute. > > > > > > Changes in the v3 patch. > > > > > > 1. GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS support has been added to > > > GNU binutils 2.38. But the -z indirect-extern-access linker option is > > > only available for Linux/x86. However, the --max-cache-size=SIZE linker > > > option was also addded within a day. --max-cache-size=SIZE is used to > > > check for GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS support. > > > > > > Changes in the v2 patch. > > > > > > 1. Rename the option to -fdirect-extern-access. > > > > > > --- > > > On systems with copy relocation: > > > * A copy in executable is created for the definition in a shared library > > > at run-time by ld.so. > > > * The copy is referenced by executable and shared libraries. > > > * Executable can access the copy directly. > > > > > > Issues are: > > > * Overhead of a copy, time and space, may be visible at run-time. > > > * Read-only data in the shared library becomes read-write copy in > > > executable at run-time. > > > * Local access to data with the STV_PROTECTED visibility in the shared > > > library must use GOT. > > > > > > On systems without function descriptor, function pointers vary depending > > > on where and how the functions are defined. > > > * If the function is defined in executable, it can be the address of > > > function body. > > > * If the function, including the function with STV_PROTECTED visibility, > > > is defined in the shared library, it can be the address of the PLT entry > > > in executable or shared library. > > > > > > Issues are: > > > * The address of function body may not be used as its function pointer. > > > * ld.so needs to search loaded shared libraries for the function pointer > > > of the function with STV_PROTECTED visibility. > > > > > > Here is a proposal to remove copy relocation and use canonical function > > > pointer: > > > > > > 1. Accesses, including in PIE and non-PIE, to undefined symbols must > > > use GOT. > > > a. Linker may optimize out GOT access if the data is defined in PIE or > > > non-PIE. > > > 2. Read-only data in the shared library remain read-only at run-time > > > 3. Address of global data with the STV_PROTECTED visibility in the shared > > > library is the address of data body. > > > a. Can use IP-relative access. > > > b. May need GOT without IP-relative access. > > > 4. For systems without function descriptor, > > > a. All global function pointers of undefined functions in PIE and > > > non-PIE must use GOT. Linker may optimize out GOT access if the > > > function is defined in PIE or non-PIE. > > > b. Function pointer of functions with the STV_PROTECTED visibility in > > > executable and shared library is the address of function body. > > > i. Can use IP-relative access. > > > ii. May need GOT without IP-relative access. > > > iii. Branches to undefined functions may use PLT. > > > 5. Single global definition marker: > > > > > > Add GNU_PROPERTY_1_NEEDED: > > > > > > #define GNU_PROPERTY_1_NEEDED GNU_PROPERTY_UINT32_OR_LO > > > > > > to indicate the needed properties by the object file. > > > > > > Add GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS: > > > > > > #define GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS (1U << 0) > > > > > > to indicate that the object file requires canonical function pointers and > > > cannot be used with copy relocation. This bit should be cleared in > > > executable when there are non-GOT or non-PLT relocations in relocatable > > > input files without this bit set. > > > > > > a. Protected symbol access within the shared library can be treated as > > > local. > > > b. Copy relocation should be disallowed at link-time and run-time. > > > c. GOT function pointer reference is required at link-time and run-time. > > > > > > The indirect external access marker can be used in the following ways: > > > > > > 1. Linker can decide the best way to resolve a relocation against a > > > protected symbol before seeing all relocations against the symbol. > > > 2. Dynamic linker can decide if it is an error to have a copy relocation > > > in executable against the protected symbol in a shared library by checking > > > if the shared library is built with -fno-direct-extern-access. > > > > > > Add a compiler option, -fdirect-extern-access. -fdirect-extern-access is > > > the default. With -fno-direct-extern-access: > > > > > > 1. Always to use GOT to access undefined symbols, including in PIE and > > > non-PIE. This is safe to do and does not break the ABI. > > > 2. In executable and shared library, for symbols with the STV_PROTECTED > > > visibility: > > > a. The address of data symbol is the address of data body. > > > b. For systems without function descriptor, the function pointer is > > > the address of function body. > > > These break the ABI and resulting shared libraries may not be compatible > > > with executables which are not compiled with -fno-direct-extern-access. > > > 3. Generate an indirect external access marker in relocatable objects if > > > supported by linker. > > > > > > H.J. Lu (2): > > > Add -f[no-]direct-extern-access > > > Add TARGET_ASM_EMIT_GNU_PROPERTY_NOTE > > > > > > > Hi, > > > > This has been implemented in binutils 2.38 and glibc 2.35. > > What do I need to do to get it into GCC 12? > > > > Hi Richard, Jeff, > > Can you help review this patch for GCC 12: > > https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580108.html > https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580107.html > PING. -- H.J.