From patchwork Sun Oct 17 00:50:20 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fangrui Song X-Patchwork-Id: 46309 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id D715D3857C4B for ; Sun, 17 Oct 2021 00:51:53 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org D715D3857C4B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1634431913; bh=AvUUcmvZqrLN+W5dkUE5LSfm59nrqJWAMIc/5KbUZKU=; h=Date:Subject:To:List-Id:List-Unsubscribe:List-Archive:List-Post: List-Help:List-Subscribe:From:Reply-To:Cc:From; b=XihaYnT8+NAJLQzhmocfsw++q4yeJmhez8tHzczu9NE9s7GAdy+NMo7NULhMJVGZs b0ieBy1zuGxO8DU1GZgYvPgAaGe4WN+jNb8PmEZoZuHLHFRqFV7EGdJtcIzsRvu8o7 SdyoTLuVtGbe/57+etQpNAJb20tFhjFDHbICnd1U= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by sourceware.org (Postfix) with ESMTPS id D44353858C60 for ; Sun, 17 Oct 2021 00:50:28 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org D44353858C60 Received: by mail-yb1-xb4a.google.com with SMTP id t7-20020a258387000000b005b6d7220c79so15441600ybk.16 for ; Sat, 16 Oct 2021 17:50:28 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=AvUUcmvZqrLN+W5dkUE5LSfm59nrqJWAMIc/5KbUZKU=; b=zMiGYt4/+C1D1OCqiHYx8IjIg3rYl/aQZQPkRumv40hHsqV5sDGhct19+ZSPquQFQg KuWgT8abVH7f0HVuxiPcI4fKoA7jUJJBgHKHtdvSuagqwzSPIto1UvUMHljN+efSsrCw k8nPaHipjFdpdCoPpxyPqVh4JPmpKXCodj74MYE0MmJ0zOoOok+FUKB9aIgIlYE+FsZM YIGbe0PHGQvZPniWeeHyLHKwDubzD/Z8/IKUppDbDKjrLBntNPqmjVBsNw0KGKUwHqUt eJHha+zkPiMPIFNRFA3ekIOH35v4WwkvDbmwYA1GNCL4kuYtCymnY4ClUygv/Q9i0pTF LxVw== X-Gm-Message-State: AOAM532Gf8NVixP3FrMecW4PU55DT87pHnyle2N3nbgPED3GvckVFGZ8 ueb3lzTd5TKMJSvBGs8VLuaz084OaGgdx9G4NcU0YTGldvBgwAA3itn4RT1KMlIrGwwY2VVmQe1 Yl6/RYq7hHYYGxxAT563JR063teDuD+yHD2ZvIu9xw6syz70ZkrUhuX7S/N104z2AzV1A X-Google-Smtp-Source: ABdhPJz5+pjJYxasyjE4kEa/aj8DqC5WfB5VfBtMpkbbI8vWzObXoQlnmBrfVPU/YuhxLHfqW7aaulA+X8qj X-Received: from maskray1.svl.corp.google.com ([2620:15c:2ce:200:1d42:3a53:f2e6:ae05]) (user=maskray job=sendgmr) by 2002:a25:217:: with SMTP id 23mr21536349ybc.205.1634431828426; Sat, 16 Oct 2021 17:50:28 -0700 (PDT) Date: Sat, 16 Oct 2021 17:50:20 -0700 Message-Id: <20211017005020.2645717-1-maskray@google.com> Mime-Version: 1.0 Subject: [PATCH v2] elf: Support DT_RELR relative relocation format [BZ #27924] To: libc-alpha@sourceware.org X-Spam-Status: No, score=-19.6 required=5.0 tests=BAYES_00, DKIMWL_WL_MED, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, USER_IN_DEF_DKIM_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-Patchwork-Original-From: Fangrui Song via Libc-alpha From: Fangrui Song Reply-To: Fangrui Song Cc: binutils@sourceware.org Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" PIE and shared objects usually have many relative relocations. In 2017/2018, SHT_RELR/DT_RELR was proposed on https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/GxjM0L-PBAAJ ("Proposal for a new section type SHT_RELR") and is a pre-standard. RELR usually takes 3% or smaller space than R_*_RELATIVE relocations. The virtual memory size of a mostly statically linked PIE is typically 5~10% smaller. --- Notes I will not include in the submitted commit: Available on https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/relr "pre-standard": even Solaris folks are happy with the refined generic-abi proposal. Cary Coutant will apply the change https://sourceware.org/pipermail/libc-alpha/2021-October/131781.html This patch is simpler than Chrome OS's glibc patch and makes ELF_DYNAMIC_DO_RELR available to all ports. I don't think the current glibc implementation supports ia64 in an ELFCLASS32 container. That said, the style I used is works with an ELFCLASS32 container for 64-bit machine if ElfW(Addr) is 64-bit. * Chrome OS folks have carried a local patch since 2018 (latest version: https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-libs/glibc/files/local/glibc-2.32). I.e. this feature has been battle tested. * Android bionic supports 2018 and switched to DT_RELR==36 in 2020. * The Linux kernel has supported CONFIG_RELR since 2019-08 (https://git.kernel.org/linus/5cf896fb6be3effd9aea455b22213e27be8bdb1d). * A musl patch (by me) exists but is not applied: https://www.openwall.com/lists/musl/2019/03/06/3 * rtld-elf from FreeBSD 14 will support DT_RELR. I believe upstream glibc should support DT_RELR to benefit all Linux distributions. I filed some feature requests to get their attention: * Gentoo: https://bugs.gentoo.org/818376 * Arch Linux: https://bugs.archlinux.org/task/72433 * Debian https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996598 * Fedora https://bugzilla.redhat.com/show_bug.cgi?id=2014699 As of linker support (to the best of my knowledge): * LLD support DT_RELR. * https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/main/sys-devel/binutils/files/ has a gold patch. * GNU ld feature request https://sourceware.org/bugzilla/show_bug.cgi?id=27923 I wish that GNU ld and gold maintainers can implement the feature as well :) Tested on aarch64 and x86_64. Changes from v1 (https://sourceware.org/pipermail/libc-alpha/2021-October/131768.html) * Fix style, simplify code * Improve test --- configure | 31 +++++++++++++++++++++++++++++++ configure.ac | 4 ++++ elf/Makefile | 4 ++++ elf/dynamic-link.h | 28 ++++++++++++++++++++++++++++ elf/elf.h | 13 +++++++++++-- elf/get-dynamic-info.h | 3 +++ elf/tst-relr.c | 27 +++++++++++++++++++++++++++ 7 files changed, 108 insertions(+), 2 deletions(-) create mode 100644 elf/tst-relr.c diff --git a/configure b/configure index 3227e434d3..fdab6a97ef 100755 --- a/configure +++ b/configure @@ -6067,6 +6067,37 @@ $as_echo "$libc_linker_feature" >&6; } config_vars="$config_vars have-depaudit = $libc_cv_depaudit" +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --pack-dyn-relocs=relr" >&5 +$as_echo_n "checking for linker that supports --pack-dyn-relocs=relr... " >&6; } +libc_linker_feature=no +if test x"$gnu_ld" = x"yes"; then + cat > conftest.c <&5 + (eval $ac_try) 2>&5 + ac_status=$? + $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5 + test $ac_status = 0; }; } + then + libc_linker_feature=yes + fi + rm -f conftest* +fi +if test $libc_linker_feature = yes; then + libc_cv_relr=yes +else + libc_cv_relr=no +fi +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5 +$as_echo "$libc_linker_feature" >&6; } +config_vars="$config_vars +have-relr = $libc_cv_relr" + { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5 $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; } libc_linker_feature=no diff --git a/configure.ac b/configure.ac index 00f49f09f7..96110f9d7d 100644 --- a/configure.ac +++ b/configure.ac @@ -1354,6 +1354,10 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x], [libc_cv_depaudit=yes], [libc_cv_depaudit=no]) LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit]) +LIBC_LINKER_FEATURE([--pack-dyn-relocs=relr], [-Wl,--pack-dyn-relocs=relr], + [libc_cv_relr=yes], [libc_cv_relr=no]) +LIBC_CONFIG_VAR([have-relr], [$libc_cv_relr]) + LIBC_LINKER_FEATURE([--no-dynamic-linker], [-Wl,--no-dynamic-linker], [libc_cv_no_dynamic_linker=yes], diff --git a/elf/Makefile b/elf/Makefile index bf45d8ee24..2c4cdfac68 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -245,6 +245,10 @@ tests-special += $(objpfx)tst-audit14-cmp.out $(objpfx)tst-audit15-cmp.out \ $(objpfx)tst-audit16-cmp.out endif endif +ifeq ($(have-relr),yes) +tests += tst-relr +LDFLAGS-tst-relr += -Wl,--pack-dyn-relocs=relr +endif endif tests += $(tests-execstack-$(have-z-execstack)) ifeq ($(run-built-tests),yes) diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h index ac4cc70dea..fafd42f918 100644 --- a/elf/dynamic-link.h +++ b/elf/dynamic-link.h @@ -160,6 +160,33 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[], # define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */ # endif +# define ELF_DYNAMIC_DO_RELR(map) \ + do { \ + ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \ + const ElfW(Relr) *r, *end; \ + if (!(map)->l_info[DT_RELR]) \ + break; \ + r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \ + end = (const ElfW(Relr) *)((const char *)r + \ + (map)->l_info[DT_RELRSZ]->d_un.d_val); \ + for (; r < end; r++) \ + { \ + ElfW(Relr) entry = *r; \ + if ((entry & 1) == 0) \ + { \ + where = (ElfW(Addr) *)(l_addr + entry); \ + *where++ += l_addr; \ + } \ + else \ + { \ + for (long i = 0; (entry >>= 1) != 0; i++) \ + if ((entry & 1) != 0) \ + where[i] += l_addr; \ + where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \ + } \ + } \ + } while (0); + /* This can't just be an inline function because GCC is too dumb to inline functions containing inlines themselves. */ # define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \ @@ -168,6 +195,7 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[], (consider_profile)); \ ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \ ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \ + ELF_DYNAMIC_DO_RELR ((map)); \ } while (0) #endif diff --git a/elf/elf.h b/elf/elf.h index 50f87baceb..6dc1ee0ac0 100644 --- a/elf/elf.h +++ b/elf/elf.h @@ -443,7 +443,8 @@ typedef struct #define SHT_PREINIT_ARRAY 16 /* Array of pre-constructors */ #define SHT_GROUP 17 /* Section group */ #define SHT_SYMTAB_SHNDX 18 /* Extended section indices */ -#define SHT_NUM 19 /* Number of defined types. */ +#define SHT_RELR 19 /* RELR relative relocations */ +#define SHT_NUM 20 /* Number of defined types. */ #define SHT_LOOS 0x60000000 /* Start OS-specific. */ #define SHT_GNU_ATTRIBUTES 0x6ffffff5 /* Object attributes. */ #define SHT_GNU_HASH 0x6ffffff6 /* GNU-style hash table. */ @@ -662,6 +663,11 @@ typedef struct Elf64_Sxword r_addend; /* Addend */ } Elf64_Rela; +/* RELR relocation table entry */ + +typedef Elf32_Word Elf32_Relr; +typedef Elf64_Xword Elf64_Relr; + /* How to extract and insert information held in the r_info field. */ #define ELF32_R_SYM(val) ((val) >> 8) @@ -887,7 +893,10 @@ typedef struct #define DT_PREINIT_ARRAY 32 /* Array with addresses of preinit fct*/ #define DT_PREINIT_ARRAYSZ 33 /* size in bytes of DT_PREINIT_ARRAY */ #define DT_SYMTAB_SHNDX 34 /* Address of SYMTAB_SHNDX section */ -#define DT_NUM 35 /* Number used */ +#define DT_RELRSZ 35 /* Total size of RELR relative relocations */ +#define DT_RELR 36 /* Address of RELR relative relocations */ +#define DT_RELRENT 37 /* Size of one RELR relative relocaction */ +#define DT_NUM 38 /* Number used */ #define DT_LOOS 0x6000000d /* Start of OS-specific */ #define DT_HIOS 0x6ffff000 /* End of OS-specific */ #define DT_LOPROC 0x70000000 /* Start of processor-specific */ diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h index 1ac0663d1f..ce0151c2b4 100644 --- a/elf/get-dynamic-info.h +++ b/elf/get-dynamic-info.h @@ -88,6 +88,7 @@ elf_get_dynamic_info (struct link_map *l) # if ! ELF_MACHINE_NO_REL ADJUST_DYN_INFO (DT_REL); # endif + ADJUST_DYN_INFO (DT_RELR); ADJUST_DYN_INFO (DT_JMPREL); ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM)); ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH)); @@ -112,6 +113,8 @@ elf_get_dynamic_info (struct link_map *l) if (info[DT_REL] != NULL) assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel))); #endif + if (info[DT_RELR] != NULL) + assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr))); #ifdef STATIC_PIE_BOOTSTRAP assert (info[DT_RUNPATH] == NULL); assert (info[DT_RPATH] == NULL); diff --git a/elf/tst-relr.c b/elf/tst-relr.c new file mode 100644 index 0000000000..79736a4a8a --- /dev/null +++ b/elf/tst-relr.c @@ -0,0 +1,27 @@ +static int o, x; + +#define ELEMS O O O O O O O O X X X X X X X O O X O O X X X E X E E O X O E +#define E 0, + +#define O &o, +#define X &x, +void *arr[] = { ELEMS }; +#undef O +#undef X + +#define O 1, +#define X 2, +static char val[] = { ELEMS }; + +static int +do_test (void) +{ + for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++) + if (!((arr[i] == 0 && val[i] == 0) || + (arr[i] == &o && val[i] == 1) || + (arr[i] == &x && val[i] == 2))) + return 1; + return 0; +} + +#include