[v2] ld: Add --export-dynamic-symbol

Message ID 20200505020958.wznlemr2f5yciape@google.com
State New
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  • [v2] ld: Add --export-dynamic-symbol
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Commit Message

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

Comments

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.
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)

If you think we can correct this, I think it should be fine.
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.

> If you think we can correct this, I think it should be fine.


Please open a gold bug for this.

Thanks.

-- 
H.J.

Patch

From 99fd9237fae0ce8ad5a5063d8647f944503cab97 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Wed, 22 Apr 2020 22:12:42 -0700
Subject: [PATCH v2] ld: Add --export-dynamic-symbol

	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.
	* testsuite/ld-undefined/export-dynamic-symbol-2.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-2.d    |  8 +++++
 .../ld-undefined/export-dynamic-symbol.exp    | 35 +++++++++++++++++++
 8 files changed, 95 insertions(+)
 create mode 100644 ld/testsuite/ld-undefined/export-dynamic-symbol-1.d
 create mode 100644 ld/testsuite/ld-undefined/export-dynamic-symbol-2.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
+#nm: -D
+
+#...
+[0-9a-f]+ T +foo
+#...
diff --git a/ld/testsuite/ld-undefined/export-dynamic-symbol-2.d b/ld/testsuite/ld-undefined/export-dynamic-symbol-2.d
new file mode 100644
index 0000000000..3edfbb5b74
--- /dev/null
+++ b/ld/testsuite/ld-undefined/export-dynamic-symbol-2.d
@@ -0,0 +1,8 @@ 
+#name: --export-dynamic-symbol not_exist
+#source: require-defined.s
+#ld: -pie --export-dynamic-symbol not_exist
+#nm: -n
+
+#...
+ + U not_exist
+#...
diff --git a/ld/testsuite/ld-undefined/export-dynamic-symbol.exp b/ld/testsuite/ld-undefined/export-dynamic-symbol.exp
new file mode 100644
index 0000000000..247ccf2660
--- /dev/null
+++ b/ld/testsuite/ld-undefined/export-dynamic-symbol.exp
@@ -0,0 +1,35 @@ 
+# Expect script for ld --export-dynamic-symbol tests
+#   Copyright (C) 2020 Free Software Foundation, Inc.
+#
+# This file is part of the GNU Binutils.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+# MA 02110-1301, USA.
+#
+
+set build_tests {
+  {"Build libentry.a"
+   "" "" ""
+   {entry.s} {} "libentry.a"}
+}
+
+run_ld_link_tests $build_tests
+
+set test_list [lsort [glob -nocomplain $srcdir/$subdir/export-dynamic-symbol-*.d]]
+foreach t $test_list {
+    # We need to strip the ".d", but can leave the dirname.
+    verbose [file rootname $t]
+    run_dump_test [file rootname $t]
+}
-- 
2.26.2.526.g744177e7f7-goog