[PATCH v3 3/5] Add GLIBC_ABI_DT_RELR for DT_RELR support
H.J. Lu
hjl.tools@gmail.com
Tue Mar 1 15:10:58 GMT 2022
On Tue, Mar 1, 2022 at 6:42 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Feb 28, 2022 at 8:22 PM Fangrui Song <maskray@google.com> wrote:
> >
> > On 2022-02-07, H.J. Lu wrote:
> > >The EI_ABIVERSION field of the ELF header in executables and shared
> > >libraries can be bumped to indicate the minimum ABI requirement on the
> > >dynamic linker. However, EI_ABIVERSION in executables isn't checked by
> > >the Linux kernel ELF loader nor the existing dynamic linker. Executables
> > >will crash mysteriously if the dynamic linker doesn't support the ABI
> > >features required by the EI_ABIVERSION field. The dynamic linker should
> > >be changed to check EI_ABIVERSION in executables.
> > >
> > >Add a glibc version, GLIBC_ABI_DT_RELR, to indicate DT_RELR support so
> > >that the existing dynamic linkers will issue an error on executables with
> > >GLIBC_ABI_DT_RELR dependency. Issue an error if there is a DT_RELR entry
> > >without GLIBC_ABI_DT_RELR dependency nor GLIBC_PRIVATE definition.
> > >
> > >Support __placeholder_only_for_empty_version_map as the placeholder symbol
> > >used only for empty version map to generate GLIBC_ABI_DT_RELR without any
> > >symbols.
> > >---
> > > elf/Makefile | 18 ++++++++++++++++--
> > > elf/Versions | 5 +++++
> > > elf/dl-version.c | 33 +++++++++++++++++++++++++++++++--
> > > elf/libc-abi-version.exp | 1 +
> > > include/link.h | 6 ++++++
> > > scripts/abilist.awk | 2 ++
> > > scripts/versions.awk | 7 ++++++-
> > > 7 files changed, 67 insertions(+), 5 deletions(-)
> > > create mode 100644 elf/libc-abi-version.exp
> > >
> > >diff --git a/elf/Makefile b/elf/Makefile
> > >index 71b08c75dd..a6515e8a21 100644
> > >--- a/elf/Makefile
> > >+++ b/elf/Makefile
> > >@@ -48,6 +48,10 @@ routines = \
> > > rtld_static_init \
> > > # routines
> > >
> > >+ifeq ($(have-dt-relr),yes)
> > >+check-abi-version-libc = $(objpfx)check-abi-version-libc.out
> > >+endif
> > >+
> > > # The core dynamic linking functions are in libc for the static and
> > > # profiled libraries.
> > > dl-routines = \
> > >@@ -1106,8 +1110,8 @@ $(eval $(call include_dsosort_tests,dso-sort-tests-1.def))
> > > $(eval $(call include_dsosort_tests,dso-sort-tests-2.def))
> > > endif
> > >
> > >-check-abi: $(objpfx)check-abi-ld.out
> > >-tests-special += $(objpfx)check-abi-ld.out
> > >+check-abi: $(objpfx)check-abi-ld.out $(check-abi-version-libc)
> > >+tests-special += $(objpfx)check-abi-ld.out $(check-abi-version-libc)
> > > update-abi: update-abi-ld
> > > update-all-abi: update-all-abi-ld
> > >
> > >@@ -2747,3 +2751,13 @@ $(objpfx)check-tst-relr-pie.out: $(objpfx)tst-relr-pie
> > > | sed -ne '/required from libc.so/,$$ p' \
> > > | grep GLIBC_ABI_DT_RELR > $@; \
> > > $(evaluate-test)
> > >+
> > >+$(objpfx)check-abi-version-libc.out: libc-abi-version.exp \
> > >+ $(objpfx)libc.symlist-abi-version
> > >+ cmp $^ > $@; \
> > >+ $(evaluate-test)
> > >+
> > >+$(objpfx)libc.symlist-abi-version: $(common-objpfx)libc.so
> > >+ LC_ALL=C $(NM) -D $< | grep " GLIBC_ABI_" \
> > >+ | sed "s/^0\+/00000000/" > $@T
> > >+ mv -f $@T $@
> >
> > This checks the SHN_ABS symbol.
> > ld.lld does not add the SHN_ABS symbol and does not plan to add it as,
> > Perhaps just check the placeholder symbol.
>
> Does lld support version dependency without a symbol?
> I want to avoid adding the unused symbols to libc.so.
>
> > GNU nm before binutils 2.35 does not display @ or @@ in -D mode.
>
> I will check it.
check-abi-version-libc.out doesn't depend on DT_RELR support in
binutils. I will update it.
> > >diff --git a/elf/Versions b/elf/Versions
> > >index 8bed855d8c..a9ff278de7 100644
> > >--- a/elf/Versions
> > >+++ b/elf/Versions
> > >@@ -23,6 +23,11 @@ libc {
> > > GLIBC_2.35 {
> > > _dl_find_object;
> > > }
> > >+ GLIBC_ABI_DT_RELR {
> > >+ # This symbol is used only for empty version map and will be removed
> > >+ # by scripts/versions.awk.
> > >+ __placeholder_only_for_empty_version_map;
> > >+ }
> > > GLIBC_PRIVATE {
> > > # functions used in other libraries
> > > __libc_early_init;
> > >diff --git a/elf/dl-version.c b/elf/dl-version.c
> > >index b47bd91727..720ec596a5 100644
> > >--- a/elf/dl-version.c
> > >+++ b/elf/dl-version.c
> > >@@ -214,12 +214,20 @@ _dl_check_map_versions (struct link_map *map, int verbose, int trace_mode)
> > > while (1)
> > > {
> > > /* Match the symbol. */
> > >+ const char *string = strtab + aux->vna_name;
> > > result |= match_symbol (DSO_FILENAME (map->l_name),
> > > map->l_ns, aux->vna_hash,
> > >- strtab + aux->vna_name,
> > >- needed->l_real, verbose,
> > >+ string, needed->l_real, verbose,
> > > aux->vna_flags & VER_FLG_WEAK);
> > >
> > >+ if (map->l_abi_version == lav_none
> > >+ /* 0xfd0e42: _dl_elf_hash ("GLIBC_ABI_DT_RELR"). */
> > >+ && aux->vna_hash == 0xfd0e42
> > >+ && __glibc_likely (strcmp (string,
> > >+ "GLIBC_ABI_DT_RELR")
> > >+ == 0))
> > >+ map->l_abi_version = lav_dt_relr_ref;
> > >+
> > > /* Compare the version index. */
> > > if ((unsigned int) (aux->vna_other & 0x7fff) > ndx_high)
> > > ndx_high = aux->vna_other & 0x7fff;
> > >@@ -253,6 +261,16 @@ _dl_check_map_versions (struct link_map *map, int verbose, int trace_mode)
> > > ent = (ElfW(Verdef) *) (map->l_addr + def->d_un.d_ptr);
> > > while (1)
> > > {
> > >+ /* 0x0963cf85: _dl_elf_hash ("GLIBC_PRIVATE"). */
> > >+ if (ent->vd_hash == 0x0963cf85)
> > >+ {
> > >+ ElfW(Verdaux) *aux = (ElfW(Verdaux) *) ((char *) ent
> > >+ + ent->vd_aux);
> > >+ if (__glibc_likely (strcmp ("GLIBC_PRIVATE",
> > >+ strtab + aux->vda_name) == 0))
> > >+ map->l_abi_version = lav_private_def;
> > >+ }
> > >+
> > > if ((unsigned int) (ent->vd_ndx & 0x7fff) > ndx_high)
> > > ndx_high = ent->vd_ndx & 0x7fff;
> > >
> > >@@ -352,6 +370,17 @@ _dl_check_map_versions (struct link_map *map, int verbose, int trace_mode)
> > > }
> > > }
> > >
> > >+ /* Issue an error if there is a DT_RELR entry without GLIBC_ABI_DT_RELR
> > >+ dependency nor GLIBC_PRIVATE definition. */
> > >+ if (map->l_info[DT_RELR] != NULL
> > >+ && __glibc_unlikely (map->l_abi_version == lav_none))
> > >+ {
> > >+ _dl_exception_create
> > >+ (&exception, DSO_FILENAME (map->l_name),
> > >+ N_("DT_RELR without GLIBC_ABI_DT_RELR dependency"));
> > >+ goto call_error;
> > >+ }
> > >+
> > > return result;
> > > }
> > >
> > >diff --git a/elf/libc-abi-version.exp b/elf/libc-abi-version.exp
> > >new file mode 100644
> > >index 0000000000..455088dc6b
> > >--- /dev/null
> > >+++ b/elf/libc-abi-version.exp
> > >@@ -0,0 +1 @@
> > >+00000000 A GLIBC_ABI_DT_RELR
> > >diff --git a/include/link.h b/include/link.h
> > >index bef2820b40..ce9e3d5214 100644
> > >--- a/include/link.h
> > >+++ b/include/link.h
> > >@@ -177,6 +177,12 @@ struct link_map
> > > lt_library, /* Library needed by main executable. */
> > > lt_loaded /* Extra run-time loaded shared object. */
> > > } l_type:2;
> > >+ enum /* ABI dependency of this object. */
> > >+ {
> > >+ lav_none, /* No ABI dependency. */
> > >+ lav_dt_relr_ref, /* Need GLIBC_ABI_DT_RELR. */
> > >+ lav_private_def /* Define GLIBC_PRIVATE. */
> > >+ } l_abi_version:2;
> > > unsigned int l_relocated:1; /* Nonzero if object's relocations done. */
> > > unsigned int l_init_called:1; /* Nonzero if DT_INIT function called. */
> > > unsigned int l_global:1; /* Nonzero if object in _dl_global_scope. */
> > >diff --git a/scripts/abilist.awk b/scripts/abilist.awk
> > >index 24a34ccbed..6cc7af6ac8 100644
> > >--- a/scripts/abilist.awk
> > >+++ b/scripts/abilist.awk
> > >@@ -55,6 +55,8 @@ $2 == "g" || $2 == "w" && (NF == 7 || NF == 8) {
> > > # caused STV_HIDDEN symbols to appear in .dynsym, though that is useless.
> > > if (NF > 7 && $7 == ".hidden") next;
> > >
> > >+ if (version ~ /^GLIBC_ABI_/ && !include_abi_version) next;
> > >+
> > > if (version == "GLIBC_PRIVATE" && !include_private) next;
> > >
> > > desc = "";
> > >diff --git a/scripts/versions.awk b/scripts/versions.awk
> > >index 357ad1355e..d70b07bd1a 100644
> > >--- a/scripts/versions.awk
> > >+++ b/scripts/versions.awk
> > >@@ -185,8 +185,13 @@ END {
> > > closeversion(oldver, veryoldver);
> > > veryoldver = oldver;
> > > }
> > >- printf("%s {\n global:\n", $2) > outfile;
> > > oldver = $2;
> > >+ # Skip the placeholder symbol used only for empty version map.
> > >+ if ($3 == "__placeholder_only_for_empty_version_map;") {
> > >+ printf("%s {\n", $2) > outfile;
> > >+ continue;
> > >+ }
> > >+ printf("%s {\n global:\n", $2) > outfile;
> > > }
> > > printf(" ") > outfile;
> > > for (n = 3; n <= NF; ++n) {
> > >--
> > >2.34.1
> > >
> >
> > Looks like a Serpent OS contributor has noticed this patch series
> > https://github.com/llvm/llvm-project/issues/53775#issuecomment-1046361237 .
> > I will try implementing -z pack-relative-relocs for ld.lld
>
>
>
> --
> H.J.
--
H.J.
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