[PATCH v3] ld: Add --export-dynamic-symbol

H.J. Lu hjl.tools@gmail.com
Tue May 5 20:56:43 GMT 2020


On Tue, May 5, 2020 at 9:55 AM Fangrui Song <maskray@google.com> wrote:
>
>
> On 2020-05-05, H.J. Lu wrote:
> >On Tue, May 5, 2020 at 8:30 AM Fangrui Song <maskray@google.com> wrote:
> >>
> >> On 2020-05-05, H.J. Lu wrote:
> >> >On Mon, May 4, 2020 at 7:10 PM Fangrui Song <maskray@google.com> wrote:
> >> >>
> >> >> On 2020-05-04, H.J. Lu wrote:
> >> >> >On Mon, May 4, 2020 at 10:48 AM Fangrui Song <maskray@google.com> wrote:
> >> >> >>
> >> >> >> On 2020-05-03, H.J. Lu wrote:
> >> >> >> >On Sat, May 2, 2020 at 11:15 PM Fangrui Song via Binutils
> >> >> >> ><binutils@sourceware.org> wrote:
> >> >> >> >>
> >> >> >> >>         PR ld/25910
> >> >> >> >>         * ldlang.c (export_dynamic_symbol_list): New.
> >> >> >> >>         (ldlang_add_export_dynamic_symbol): New.
> >> >> >> >>         (lang_place_export_dynamic_symbols): New.
> >> >> >> >>         (lang_process): Handle export_dynamic_symbol_list.
> >> >> >> >>         * ldlang.h (ldlang_add_export_dynamic_symbol): New.
> >> >> >> >>         * ldlex.h (option_values): Add OPTION_EXPORT_DYNAMIC_SYMBOL.
> >> >> >> >>         * lexsup.c (ld_options): Add entry for OPTION_EXPORT_DYNAMIC_SYMBOL.
> >> >> >> >>         (parse_args): Handle it.
> >> >> >> >>         * ld.texi: Add --export-dynamic-symbol documentation.
> >> >> >> >>         * testsuite/ld-undefined/export-dynamic-symbol.exp: Run new test.
> >> >> >> >>         * testsuite/ld-undefined/export-dynamic-symbol-1.d: New.
> >> >> >> >> ---
> >> >> >> >>  ld/ld.texi                                    |  8 +++++
> >> >> >> >>  ld/ldlang.c                                   | 26 ++++++++++++++
> >> >> >> >>  ld/ldlang.h                                   |  2 ++
> >> >> >> >>  ld/ldlex.h                                    |  1 +
> >> >> >> >>  ld/lexsup.c                                   |  7 ++++
> >> >> >> >>  .../ld-undefined/export-dynamic-symbol-1.d    |  8 +++++
> >> >> >> >>  .../ld-undefined/export-dynamic-symbol.exp    | 35 +++++++++++++++++++
> >> >> >> >>  7 files changed, 87 insertions(+)
> >> >> >> >>  create mode 100644 ld/testsuite/ld-undefined/export-dynamic-symbol-1.d
> >> >> >> >>  create mode 100644 ld/testsuite/ld-undefined/export-dynamic-symbol.exp
> >> >> >> >>
> >> >> >> >> diff --git a/ld/ld.texi b/ld/ld.texi
> >> >> >> >> index 4dc78e65fa..b3dc95f314 100644
> >> >> >> >> --- a/ld/ld.texi
> >> >> >> >> +++ b/ld/ld.texi
> >> >> >> >> @@ -569,6 +569,14 @@ Note that this option is specific to ELF targeted ports.  PE targets
> >> >> >> >>  support a similar function to export all symbols from a DLL or EXE; see
> >> >> >> >>  the description of @samp{--export-all-symbols} below.
> >> >> >> >>
> >> >> >> >> +@kindex --export-dynamic-symbol=@var{symbol}
> >> >> >> >> +@cindex export dynamic symbol
> >> >> >> >> +@item --export-dynamic-symbol=@var{symbol}
> >> >> >> >> +Specify a symbol that should be added to the dynamic symbol table.
> >> >> >> >> +Additionally, force @var{symbol} to be entered in the output file as an
> >> >> >> >> +undefined symbol.  Doing this may, for example, trigger linking of additional
> >> >> >> >> +modules from archives.
> >> >> >> >> +
> >> >> >> >>  @ifclear SingleFormat
> >> >> >> >>  @cindex big-endian objects
> >> >> >> >>  @cindex endianness
> >> >> >> >> diff --git a/ld/ldlang.c b/ld/ldlang.c
> >> >> >> >> index b2cdb3603a..e7ecdfeaf0 100644
> >> >> >> >> --- a/ld/ldlang.c
> >> >> >> >> +++ b/ld/ldlang.c
> >> >> >> >> @@ -3910,6 +3910,26 @@ lang_place_undefineds (void)
> >> >> >> >>      insert_undefined (ptr->name);
> >> >> >> >>  }
> >> >> >> >>
> >> >> >> >> +static struct bfd_sym_chain export_dynamic_symbol_list = { NULL, NULL };
> >> >> >> >> +
> >> >> >> >> +void
> >> >> >> >> +ldlang_add_export_dynamic_symbol (const char *const name)
> >> >> >> >> +{
> >> >> >> >> +  struct bfd_sym_chain *sym;
> >> >> >> >> +  sym = stat_alloc (sizeof (*sym));
> >> >> >> >> +  sym->name = xstrdup (name);
> >> >> >> >> +  sym->next = export_dynamic_symbol_list.next;
> >> >> >> >> +  export_dynamic_symbol_list.next = sym;
> >> >> >> >> +}
> >> >> >> >> +
> >> >> >> >> +static void
> >> >> >> >> +lang_place_export_dynamic_symbols (void)
> >> >> >> >> +{
> >> >> >> >> +  struct bfd_sym_chain *sym;
> >> >> >> >> +  for (sym = export_dynamic_symbol_list.next; sym != NULL; sym = sym->next)
> >> >> >> >> +    insert_undefined (sym->name);
> >> >> >> >> +}
> >> >> >> >> +
> >> >> >> >>  /* Structure used to build the list of symbols that the user has required
> >> >> >> >>     be defined.  */
> >> >> >> >>
> >> >> >> >> @@ -7795,6 +7815,10 @@ void
> >> >> >> >>  lang_process (void)
> >> >> >> >>  {
> >> >> >> >>    /* Finalize dynamic list.  */
> >> >> >> >> +  struct bfd_sym_chain *sym;
> >> >> >> >> +  for (sym = export_dynamic_symbol_list.next; sym != NULL; sym = sym->next)
> >> >> >> >> +    lang_append_dynamic_list (
> >> >> >> >> +        lang_new_vers_pattern (NULL, sym->name, NULL, FALSE));
> >> >> >> >>    if (link_info.dynamic_list)
> >> >> >> >>      lang_finalize_version_expr_head (&link_info.dynamic_list->head);
> >> >> >> >>
> >> >> >> >> @@ -7808,6 +7832,8 @@ lang_process (void)
> >> >> >> >>
> >> >> >> >>    /* Add to the hash table all undefineds on the command line.  */
> >> >> >> >>    lang_place_undefineds ();
> >> >> >> >> +  /* Add --export-dynamic-symbol symbols to the hash table.  */
> >> >> >> >> +  lang_place_export_dynamic_symbols ();
> >> >> >> >>
> >> >> >> >>    if (!bfd_section_already_linked_table_init ())
> >> >> >> >>      einfo (_("%F%P: can not create hash table: %E\n"));
> >> >> >> >> diff --git a/ld/ldlang.h b/ld/ldlang.h
> >> >> >> >> index 2aa3930f95..8c004b173c 100644
> >> >> >> >> --- a/ld/ldlang.h
> >> >> >> >> +++ b/ld/ldlang.h
> >> >> >> >> @@ -606,6 +606,8 @@ extern lang_output_section_statement_type *next_matching_output_section_statemen
> >> >> >> >>    (lang_output_section_statement_type *, int);
> >> >> >> >>  extern void ldlang_add_undef
> >> >> >> >>    (const char *const, bfd_boolean);
> >> >> >> >> +extern void ldlang_add_export_dynamic_symbol
> >> >> >> >> +  (const char *const);
> >> >> >> >>  extern void ldlang_add_require_defined
> >> >> >> >>    (const char *const);
> >> >> >> >>  extern void lang_add_output_format
> >> >> >> >> diff --git a/ld/ldlex.h b/ld/ldlex.h
> >> >> >> >> index 22b928d2d9..70f2da5636 100644
> >> >> >> >> --- a/ld/ldlex.h
> >> >> >> >> +++ b/ld/ldlex.h
> >> >> >> >> @@ -81,6 +81,7 @@ enum option_values
> >> >> >> >>    OPTION_DYNAMIC_LIST_CPP_NEW,
> >> >> >> >>    OPTION_DYNAMIC_LIST_CPP_TYPEINFO,
> >> >> >> >>    OPTION_DYNAMIC_LIST_DATA,
> >> >> >> >> +  OPTION_EXPORT_DYNAMIC_SYMBOL,
> >> >> >> >>    OPTION_WARN_COMMON,
> >> >> >> >>    OPTION_WARN_CONSTRUCTORS,
> >> >> >> >>    OPTION_WARN_FATAL,
> >> >> >> >> diff --git a/ld/lexsup.c b/ld/lexsup.c
> >> >> >> >> index d1955b9afa..0a0c2f2873 100644
> >> >> >> >> --- a/ld/lexsup.c
> >> >> >> >> +++ b/ld/lexsup.c
> >> >> >> >> @@ -504,6 +504,8 @@ static const struct ld_option ld_options[] =
> >> >> >> >>      '\0', NULL, N_("Use C++ typeinfo dynamic list"), TWO_DASHES },
> >> >> >> >>    { {"dynamic-list", required_argument, NULL, OPTION_DYNAMIC_LIST},
> >> >> >> >>      '\0', N_("FILE"), N_("Read dynamic list"), TWO_DASHES },
> >> >> >> >> +  { {"export-dynamic-symbol", required_argument, NULL, OPTION_EXPORT_DYNAMIC_SYMBOL},
> >> >> >> >> +    '\0', N_("SYMBOL"), N_("Read dynamic list"), TWO_DASHES },
> >> >> >> >>    { {"warn-common", no_argument, NULL, OPTION_WARN_COMMON},
> >> >> >> >>      '\0', NULL, N_("Warn about duplicate common symbols"), TWO_DASHES },
> >> >> >> >>    { {"warn-constructors", no_argument, NULL, OPTION_WARN_CONSTRUCTORS},
> >> >> >> >> @@ -1425,6 +1427,11 @@ parse_args (unsigned argc, char **argv)
> >> >> >> >>           if (opt_symbolic == symbolic)
> >> >> >> >>             opt_symbolic = symbolic_unset;
> >> >> >> >>           break;
> >> >> >> >> +       case OPTION_EXPORT_DYNAMIC_SYMBOL:
> >> >> >> >> +         ldlang_add_export_dynamic_symbol (optarg);
> >> >> >> >> +         if (opt_dynamic_list != dynamic_list_data)
> >> >> >> >> +           opt_dynamic_list = dynamic_list;
> >> >> >> >> +         break;
> >> >> >> >>         case OPTION_WARN_COMMON:
> >> >> >> >>           config.warn_common = TRUE;
> >> >> >> >>           break;
> >> >> >> >> diff --git a/ld/testsuite/ld-undefined/export-dynamic-symbol-1.d b/ld/testsuite/ld-undefined/export-dynamic-symbol-1.d
> >> >> >> >> new file mode 100644
> >> >> >> >> index 0000000000..768bf0abd6
> >> >> >> >> --- /dev/null
> >> >> >> >> +++ b/ld/testsuite/ld-undefined/export-dynamic-symbol-1.d
> >> >> >> >> @@ -0,0 +1,8 @@
> >> >> >> >> +#name: --export-dynamic-symbol foo archive
> >> >> >> >> +#source: require-defined.s
> >> >> >> >> +#ld: -pie --export-dynamic-symbol foo tmpdir/libentry.a
> >> >> >> >
> >> >> >> >I assume that it supports
> >> >> >> >
> >> >> >> >$ ld -pie --export-dynamic-symbol foo --export-dynamic-symbol bar ...
> >> >> >> >
> >> >> >> >Please add another --export-dynamic-symbol to your test.
> >> >> >> >
> >> >> >> >--
> >> >> >> >H.J.
> >> >> >>
> >> >> >> I face a test difficulty. If I add another `#nm:`, runtest complains:
> >> >> >>
> >> >> >> % cd Debug/ld
> >> >> >> % runtest --tool ld --srcdir ../../ld/testsuite/ export-dynamic-symbol.exp
> >> >> >> ...
> >> >> >> ERROR: option nm multiply set in ../../ld/testsuite/ld-undefined/export-dynamic-symbol-1.d
> >> >> >>
> >> >> >> There may also be a problem of symbol table order determinism. I don't
> >> >> >> know whether another symbol may be ordered before foo in some ports and
> >> >> >> after foo in other ports.
> >> >> >>
> >> >> >> Honestly, I think for a number of tests, even if they test generic
> >> >> >> behavior, it might be fine to restrict them to run on certain hosts,
> >> >> >> e.g. Linux x86. What I know about testing is lacking, though, I don't
> >> >> >> know what can be tested.
> >> >> >>
> >> >> >> Ideally `#nm:` should just be free-form shell scripts but unfortunately
> >> >> >> it seems to support very limited features (undocumented?)
> >> >> >
> >> >> >You can't add another #nm.  But you can pass additional options to nm.
> >> >> >
> >> >> >--
> >> >> >H.J.
> >> >>
> >> >> Attached PATCH v2.
> >> >>
> >> >> Added export-dynamic-symbol-2.d
> >> >
> >> >There is
> >> >
> >> >'--dynamic-list=DYNAMIC-LIST-FILE'
> >> >     Specify the name of a dynamic list file to the linker.  This is
> >> >     typically used when creating shared libraries to specify a list of
> >> >     global symbols whose references shouldn't be bound to the
> >> >     definition within the shared library, or creating dynamically
> >> >     linked executables to specify a list of symbols which should be
> >> >     added to the symbol table in the executable.  This option is only
> >> >     meaningful on ELF platforms which support shared libraries.
> >> >
> >> >The new --export-dynamic-symbol option puts it on command-line
> >> >and implicitly adds -u.  This makes the new option different from
> >> >--dynamic-list.  I don't think -u should be added implicitly.  If needed,
> >> >you should add another option to add -u for all symbols on dynamic
> >> >list.
> >> >
> >> >--
> >> >H.J.
> >>
> >> I would also hope gold did not add -u. I don't particularly like it (see
> >> also https://reviews.llvm.org/D43103)
> >
> >Please drop implicit -u.
>
> Done. Attached PATCH v3.
> Improved tests to check a glob pattern and multiple --export-dynamic-symbol.
>
> Moved ld-undefined/ to ld-dynamic/ since the feature is decoupled from -u now.
>
> >> If you think we can correct this, I think it should be fine.
> >
> >Please open a gold bug for this.
> >
> >Thanks.
> >
> >--
> >H.J.
>
> Filed https://sourceware.org/bugzilla/show_bug.cgi?id=25925 (--export-dynamic-symbol should drop implicit -u)
>
>
> I may have to migrate some internal projects if they rely on the
> --export-dynamic-symbol semantics, but hopefully there will not be much
> work. I am glad that --export-dynamic-symbol semantic will be orthogonal!

+ case OPTION_EXPORT_DYNAMIC_SYMBOL:
+   ldlang_add_export_dynamic_symbol (optarg);

Can you simply call

lang_append_dynamic_list (lang_new_vers_pattern (NULL, optarg, NULL, FALSE));

here?

-- 
H.J.


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