elf: Support DT_RELR relative relocation format [BZ #27924]
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.
This commit is contained in:
Fangrui Song
H.J. Lu
parent
57292f5741
commit
e895cff59a
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@ -6076,6 +6076,43 @@ $as_echo "$libc_linker_feature" >&6; }
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config_vars="$config_vars
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have-depaudit = $libc_cv_depaudit"
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z pack-relative-relocs" >&5
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$as_echo_n "checking for linker that supports -z pack-relative-relocs... " >&6; }
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libc_linker_feature=no
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if test x"$gnu_ld" = x"yes"; then
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cat > conftest.c <<EOF
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int _start (void) { return 42; }
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EOF
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if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
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-Wl,-z,pack-relative-relocs -nostdlib -nostartfiles
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-fPIC -shared -o conftest.so conftest.c
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1>&5'
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{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
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(eval $ac_try) 2>&5
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ac_status=$?
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$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
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test $ac_status = 0; }; }
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then
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if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,pack-relative-relocs -nostdlib \
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-nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
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| grep "warning: -z pack-relative-relocs ignored" > /dev/null 2>&1; then
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true
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else
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libc_linker_feature=yes
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fi
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fi
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rm -f conftest*
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fi
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if test $libc_linker_feature = yes; then
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libc_cv_dt_relr=yes
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else
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libc_cv_dt_relr=no
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fi
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
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$as_echo "$libc_linker_feature" >&6; }
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config_vars="$config_vars
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have-dt-relr = $libc_cv_dt_relr"
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports --no-dynamic-linker" >&5
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$as_echo_n "checking for linker that supports --no-dynamic-linker... " >&6; }
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libc_linker_feature=no
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@ -1336,6 +1336,11 @@ LIBC_LINKER_FEATURE([--depaudit], [-Wl,--depaudit,x],
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[libc_cv_depaudit=yes], [libc_cv_depaudit=no])
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LIBC_CONFIG_VAR([have-depaudit], [$libc_cv_depaudit])
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LIBC_LINKER_FEATURE([-z pack-relative-relocs],
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[-Wl,-z,pack-relative-relocs],
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[libc_cv_dt_relr=yes], [libc_cv_dt_relr=no])
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LIBC_CONFIG_VAR([have-dt-relr], [$libc_cv_dt_relr])
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LIBC_LINKER_FEATURE([--no-dynamic-linker],
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[-Wl,--no-dynamic-linker],
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[libc_cv_no_dynamic_linker=yes],
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25
elf/Makefile
25
elf/Makefile
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@ -542,6 +542,25 @@ tests-special += \
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# tests-special
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endif
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endif
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ifeq ($(have-dt-relr),yes)
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tests += \
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tst-relr \
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# tests
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ifeq ($(have-fpie),yes)
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tests += \
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tst-relr-pie \
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# tests
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tests-pie += \
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tst-relr-pie \
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# tests-pie
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tests-special += \
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$(objpfx)check-tst-relr-pie.out \
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# tests-special
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endif
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CFLAGS-tst-relr-pie.c += $(pie-ccflag)
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LDFLAGS-tst-relr += -Wl,-z,pack-relative-relocs
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LDFLAGS-tst-relr-pie += -Wl,-z,pack-relative-relocs
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endif
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endif
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tests-special += $(objpfx)tst-relro-ldso.out $(objpfx)tst-relro-libc.out
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@ -2789,3 +2808,9 @@ $(objpfx)check-abi-version-libc.out: $(common-objpfx)libc.so
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| sed -ne '/.gnu.version_d/, /.gnu.version_r/ p' \
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| grep GLIBC_ABI_DT_RELR > $@; \
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$(evaluate-test)
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$(objpfx)check-tst-relr-pie.out: $(objpfx)tst-relr-pie
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LC_ALL=C $(OBJDUMP) -p $< \
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| sed -ne '/required from libc.so/,$$ p' \
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| grep GLIBC_ABI_DT_RELR > $@; \
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$(evaluate-test)
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@ -146,12 +146,46 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
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# define ELF_DYNAMIC_DO_RELA(map, scope, lazy, skip_ifunc) /* Nothing to do. */
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# endif
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# define ELF_DYNAMIC_DO_RELR(map) \
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do { \
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ElfW(Addr) l_addr = (map)->l_addr, *where = 0; \
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const ElfW(Relr) *r, *end; \
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if ((map)->l_info[DT_RELR] == NULL) \
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break; \
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r = (const ElfW(Relr) *)D_PTR((map), l_info[DT_RELR]); \
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end = (const ElfW(Relr) *)((const char *)r + \
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(map)->l_info[DT_RELRSZ]->d_un.d_val); \
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for (; r < end; r++) \
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{ \
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ElfW(Relr) entry = *r; \
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if ((entry & 1) == 0) \
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{ \
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where = (ElfW(Addr) *)(l_addr + entry); \
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*where++ += l_addr; \
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} \
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else \
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{ \
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for (long int i = 0; (entry >>= 1) != 0; i++) \
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if ((entry & 1) != 0) \
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where[i] += l_addr; \
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where += CHAR_BIT * sizeof(ElfW(Relr)) - 1; \
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} \
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} \
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} while (0);
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/* This can't just be an inline function because GCC is too dumb
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to inline functions containing inlines themselves. */
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# ifdef RTLD_BOOTSTRAP
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# define DO_RTLD_BOOTSTRAP 1
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# else
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# define DO_RTLD_BOOTSTRAP 0
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# endif
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# define ELF_DYNAMIC_RELOCATE(map, scope, lazy, consider_profile, skip_ifunc) \
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do { \
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int edr_lazy = elf_machine_runtime_setup ((map), (scope), (lazy), \
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(consider_profile)); \
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if (((map) != &GL(dl_rtld_map) || DO_RTLD_BOOTSTRAP)) \
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ELF_DYNAMIC_DO_RELR (map); \
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ELF_DYNAMIC_DO_REL ((map), (scope), edr_lazy, skip_ifunc); \
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ELF_DYNAMIC_DO_RELA ((map), (scope), edr_lazy, skip_ifunc); \
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} while (0)
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@ -89,6 +89,7 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
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# if ! ELF_MACHINE_NO_REL
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ADJUST_DYN_INFO (DT_REL);
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# endif
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ADJUST_DYN_INFO (DT_RELR);
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ADJUST_DYN_INFO (DT_JMPREL);
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ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
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ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
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@ -113,6 +114,8 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
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if (info[DT_REL] != NULL)
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assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
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#endif
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if (info[DT_RELR] != NULL)
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assert (info[DT_RELRENT]->d_un.d_val == sizeof (ElfW(Relr)));
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if (bootstrap || static_pie_bootstrap)
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{
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assert (info[DT_RUNPATH] == NULL);
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@ -0,0 +1 @@
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#include "tst-relr.c"
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@ -0,0 +1,65 @@
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/* Basic tests for DT_RELR.
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <link.h>
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#include <stdbool.h>
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#include <array_length.h>
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#include <support/check.h>
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static int o, x;
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#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
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#define E 0,
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#define O &o,
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#define X &x,
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void *arr[] = { ELEMS };
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#undef O
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#undef X
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#define O 1,
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#define X 2,
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static char val[] = { ELEMS };
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static int
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do_test (void)
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{
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ElfW(Dyn) *d = _DYNAMIC;
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if (d)
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{
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bool has_relr = false;
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for (; d->d_tag != DT_NULL; d++)
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if (d->d_tag == DT_RELR)
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has_relr = true;
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#if defined __PIE__ || defined __pie__ || defined PIE || defined pie
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TEST_VERIFY (has_relr);
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#else
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TEST_VERIFY (!has_relr);
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#endif
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}
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for (int i = 0; i < array_length (arr); i++)
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TEST_VERIFY ((arr[i] == 0 && val[i] == 0)
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|| (arr[i] == &o && val[i] == 1)
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|| (arr[i] == &x && val[i] == 2));
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return 0;
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}
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#include <support/test-driver.c>
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