From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-x230.google.com (mail-oi1-x230.google.com [IPv6:2607:f8b0:4864:20::230]) by sourceware.org (Postfix) with ESMTPS id D57D53858C53 for ; Wed, 20 Apr 2022 13:44:26 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org D57D53858C53 Received: by mail-oi1-x230.google.com with SMTP id z8so2082713oix.3 for ; Wed, 20 Apr 2022 06:44:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=Ga38SsbLi5gWabHOGEdfgqcqyg2dQQqfFlj1Kcbt7iQ=; b=JYP94hAf06iGeoRM6JIySK6x8npKpIbVWFeRiBUip7jqY+O5xD2OkJzRgrDcF0aa3J vZdx68lqydUJ8Lwj8W4EXgn7Bsr7vYJz51TcAdnBLTmpQmBj668tjYBKXyhC9Zg5wpEr EdZUKCKBKPYacD+akaB/WO5biBin+Fg7J9cAXgDotSx2VRnikdAr8WWZ8e8LJoMHHeOL UeM3YNyVLxwf7x0JAJ/jcwAtk/TFWixkk2OPOpxhB0fxbiO1SzS4WFtM+c33kV1389kv NgyOiQ+xB/WopT1ueCd+0oZt6dz3mitne6hF9r5l6A5hKsxkDcS+oayy1BGT+IG7S6hU 2QlQ== X-Gm-Message-State: AOAM5312fsOi1oEnqrMHl+TcopFzl9/gh1a22K0LY5Zy6lEWgBVUh6fc ocfDiFlOmPW0BtTjorMtBvsi9A== X-Google-Smtp-Source: ABdhPJyjjqaYbLxwLAXuUFimOl2L4tEyeAUhm1p7oRYk3QP0SXwGQfxeKeKebta0sDXNhhycyLcTJg== X-Received: by 2002:a05:6808:118b:b0:2cf:761c:184d with SMTP id j11-20020a056808118b00b002cf761c184dmr1716661oil.87.1650462265959; Wed, 20 Apr 2022 06:44:25 -0700 (PDT) Received: from ?IPV6:2804:431:c7ca:c9d0:24b1:bd98:2ef4:714c? ([2804:431:c7ca:c9d0:24b1:bd98:2ef4:714c]) by smtp.gmail.com with ESMTPSA id c3-20020a056808138300b002f76b9a9ef6sm6501092oiw.10.2022.04.20.06.44.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Apr 2022 06:44:25 -0700 (PDT) Message-ID: Date: Wed, 20 Apr 2022 10:44:22 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v10 3/7] elf: Support DT_RELR relative relocation format [BZ #27924] Content-Language: en-US To: "H.J. Lu" , libc-alpha@sourceware.org References: <20220414232129.1886210-1-hjl.tools@gmail.com> <20220414232129.1886210-4-hjl.tools@gmail.com> From: Adhemerval Zanella In-Reply-To: <20220414232129.1886210-4-hjl.tools@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-14.1 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE, URIBL_BLACK 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: Wed, 20 Apr 2022 13:44:31 -0000 On 14/04/2022 20:21, H.J. Lu wrote: > From: Fangrui Song > > 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 > > Changes from the original patch: > > 1. Check the linker option, -z pack-relative-relocs, which add a > GLIBC_ABI_DT_RELR symbol version dependency on the shared C library if > it provides a GLIBC_2.XX symbol version. > 2. Change make variale to have-dt-relr. > 3. Rename tst-relr-no-pie to tst-relr-pie for --disable-default-pie. > 4. Use TEST_VERIFY in tst-relr.c. > 5. Add the check-tst-relr-pie.out test to check for linker generated > libc.so version dependency on GLIBC_ABI_DT_RELR. > 6. Move ELF_DYNAMIC_DO_RELR before ELF_DYNAMIC_DO_REL. Patch looks good, only a small nit below. Reviewed-by: Adhemerval Zanella > --- > configure | 37 ++++++++++++++++++++++++ > configure.ac | 5 ++++ > elf/Makefile | 25 ++++++++++++++++ > elf/dynamic-link.h | 34 ++++++++++++++++++++++ > elf/get-dynamic-info.h | 3 ++ > elf/tst-relr-pie.c | 1 + > elf/tst-relr.c | 65 ++++++++++++++++++++++++++++++++++++++++++ > 7 files changed, 170 insertions(+) > create mode 100644 elf/tst-relr-pie.c > create mode 100644 elf/tst-relr.c > > diff --git a/configure b/configure > index d2f413d05d..c0c2246597 100755 > --- a/configure > +++ b/configure > @@ -6076,6 +6076,43 @@ $as_echo "$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 -z pack-relative-relocs" >&5 > +$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; } > +libc_linker_feature=no > +if test x"$gnu_ld" = x"yes"; then > + cat > conftest.c < +int _start (void) { return 42; } > +EOF > + if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp > + -Wl,-z,pack-relative-relocs -nostdlib -nostartfiles > + -fPIC -shared -o conftest.so conftest.c > + 1>&5' > + { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5 > + (eval $ac_try) 2>&5 > + ac_status=$? > + $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5 > + test $ac_status = 0; }; } > + then > + if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \ > + -nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \ > + | grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then > + true > + else > + libc_linker_feature=yes > + fi > + fi > + rm -f conftest* > +fi > +if test $libc_linker_feature = yes; then > + libc_cv_dt_relr=yes > +else > + libc_cv_dt_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-dt-relr = $libc_cv_dt_relr" > + > { $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5 > $as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; } > libc_linker_feature=no > diff --git a/configure.ac b/configure.ac > index b6a747dece..66cad71431 100644 > --- a/configure.ac > +++ b/configure.ac > @@ -1336,6 +1336,11 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x], > [libc_cv_depaudit=yes], [libc_cv_depaudit=no]) > LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit]) > > +LIBC_LINKER_FEATURE([-z pack-relative-relocs], > + [-Wl,-z,pack-relative-relocs], > + [libc_cv_dt_relr=yes], [libc_cv_dt_relr=no]) > +LIBC_CONFIG_VAR([have-dt-relr], [$libc_cv_dt_relr]) > + > LIBC_LINKER_FEATURE([--no-dynamic-linker], > [-Wl,--no-dynamic-linker], > [libc_cv_no_dynamic_linker=yes], Ok. > diff --git a/elf/Makefile b/elf/Makefile > index ee8778c3a2..3f3e711dd2 100644 > --- a/elf/Makefile > +++ b/elf/Makefile > @@ -541,6 +541,25 @@ tests-special += \ > # tests-special > endif > endif > +ifeq ($(have-dt-relr),yes) > +tests += \ > + tst-relr \ > +# tests > +ifeq ($(have-fpie),yes) > +tests += \ > + tst-relr-pie \ > +# tests > +tests-pie += \ > + tst-relr-pie \ > +# tests-pie > +tests-special += \ > + $(objpfx)check-tst-relr-pie.out \ > +# tests-special > +endif > +CFLAGS-tst-relr-pie.c += $(pie-ccflag) > +LDFLAGS-tst-relr += -Wl,-z,pack-relative-relocs > +LDFLAGS-tst-relr-pie += -Wl,-z,pack-relative-relocs > +endif > endif > > ifeq ($(run-built-tests),yes) > @@ -2743,3 +2762,9 @@ $(objpfx)check-abi-version-libc.out: $(common-objpfx)libc.so > | sed -ne '/.gnu.version_d/, /.gnu.version_r/ p' \ > | grep GLIBC_ABI_DT_RELR > $@; \ > $(evaluate-test) > + > +$(objpfx)check-tst-relr-pie.out: $(objpfx)tst-relr-pie > + LC_ALL=C $(OBJDUMP) -p $< \ > + | sed -ne '/required from libc.so/,$$ p' \ > + | grep GLIBC_ABI_DT_RELR > $@; \ > + $(evaluate-test) Ok. > diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h > index 25dd7ca4f2..7325e0d9fc 100644 > --- a/elf/dynamic-link.h > +++ b/elf/dynamic-link.h > @@ -146,12 +146,46 @@ 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]) \ Maybe check against NULL? > + 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 int i = 0; (entry >>= 1) != 0; i++) \ > + if ((entry & 1) != 0) \ > + where[i] += l_addr; \ > + where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \ > + } \ > + } \ > + } while (0); > + Ok. > /* This can't just be an inline function because GCC is too dumb > to inline functions containing inlines themselves. */ > +# ifdef RTLD_BOOTSTRAP > +# define DO_RTLD_BOOTSTRAP 1 > +# else > +# define DO_RTLD_BOOTSTRAP 0 > +# endif > # define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \ > do { \ > int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy), \ > (consider_profile)); \ > + if (((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP)) \ > + ELF_DYNAMIC_DO_RELR (map); \ > ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \ > ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \ > } while (0) Ok. > diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h > index 6c2ccd6db4..6c2a3a12b1 100644 > --- a/elf/get-dynamic-info.h > +++ b/elf/get-dynamic-info.h > @@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap, > # 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)); > @@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap, > 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))); > if (bootstrap || static_pie_bootstrap) > { > assert (info[DT_RUNPATH] == NULL); Ok. > diff --git a/elf/tst-relr-pie.c b/elf/tst-relr-pie.c > new file mode 100644 > index 0000000000..7df0cdbfd6 > --- /dev/null > +++ b/elf/tst-relr-pie.c > @@ -0,0 +1 @@ > +#include "tst-relr.c" > diff --git a/elf/tst-relr.c b/elf/tst-relr.c > new file mode 100644 > index 0000000000..c634ce0d21 > --- /dev/null > +++ b/elf/tst-relr.c > @@ -0,0 +1,65 @@ > +/* Basic tests for DT_RELR. > + Copyright (C) 2022 Free Software Foundation, Inc. > + This file is part of the GNU C Library. > + > + The GNU C Library is free software; you can redistribute it and/or > + modify it under the terms of the GNU Lesser General Public > + License as published by the Free Software Foundation; either > + version 2.1 of the License, or (at your option) any later version. > + > + The GNU C Library is distributed in the hope that it will be useful, > + but WITHOUT ANY WARRANTY; without even the implied warranty of > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > + Lesser General Public License for more details. > + > + You should have received a copy of the GNU Lesser General Public > + License along with the GNU C Library; if not, see > + . */ > + > +#include > +#include > +#include > +#include > + > +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) > +{ > + ElfW(Dyn) *d = _DYNAMIC; > + if (d) > + { > + bool has_relr = false; > + for (; d->d_tag != DT_NULL; d++) > + if (d->d_tag == DT_RELR) > + has_relr = true; > + > +#if defined __PIE__ || defined __pie__ || defined PIE || defined pie > + TEST_VERIFY (has_relr); > +#else > + TEST_VERIFY (!has_relr); > +#endif > + } > + > + for (int i = 0; i < array_length (arr); i++) > + TEST_VERIFY ((arr[i] == 0 && val[i] == 0) > + || (arr[i] == &o && val[i] == 1) > + || (arr[i] == &x && val[i] == 2)); > + > + return 0; > +} > + > +#include Ok.