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V4 [PATCH] ld: Add --export-dynamic-symbol and --export-dynamic-symbol-list

Fangrui Song maskray@google.com
Wed May 27 16:19:16 GMT 2020 
On 2020-05-27, H.J. Lu wrote:
>On Sat, May 23, 2020 at 2:56 PM Fangrui Song <maskray@google.com> wrote:
>>
>> On 2020-05-23, H.J. Lu wrote:
>> >On Sat, May 23, 2020 at 11:29 AM Fangrui Song <maskray@google.com> wrote:
>> >>
>> >> On 2020-05-23, H.J. Lu wrote:
>> >> >From: Fangrui Song <maskray@google.com>
>> >> >
>> >> >--export-dynamic-symbol-list is like a dynamic list, but without
>> >> >the symbolic property for unspecified symbols.
>> >> >
>> >> >When creating an executable, --export-dynamic-symbol-list is treated
>> >> >like --dynamic-list.
>> >> >
>> >> >When creating a shared library, it is treated like --dynamic-list if
>> >> >-Bsymbolic or --dynamic-list are used,  otherwise, it is ignored, so
>> >> >that references to matched symbols will not be bound to the definitions
>> >> >within the shared library.
>> >> >
>> >> >2020-05-XX  Fangrui Song  <maskray@google.com>
>> >> >           H.J. Lu  <hongjiu.lu@intel.com>
>> >> >
>> >> >       PR ld/25910
>> >> >       * NEWS: Mention --export-dynamic-symbol[-list].
>> >> >       * ld.texi: Document --export-dynamic-symbol[-list].
>> >> >       * ldgram.y: Pass current_dynamic_list_p to
>> >> >       lang_append_dynamic_list.
>> >> >       * ldlang.c (current_dynamic_list_p): New.
>> >> >       (ang_append_dynamic_list): Updated to take a pointer to
>> >> >       struct bfd_elf_dynamic_list * argument instead of using
>> >> >       link_info.dynamic_list.
>> >> >       (lang_append_dynamic_list_cpp_typeinfo): Pass
>> >> >       &link_info.dynamic_list to ang_append_dynamic_list.
>> >> >       (lang_append_dynamic_list_cpp_new): Likewise.
>> >> >       * ldlang.h (current_dynamic_list_p): New.
>> >> >       (lang_append_dynamic_list): Add a pointer to
>> >> >       struct bfd_elf_dynamic_list * argument.
>> >> >       * ldlex.h (option_values): Add OPTION_EXPORT_DYNAMIC_SYMBOL and
>> >> >       OPTION_EXPORT_DYNAMIC_SYMBOL_LIST.
>> >> >       * lexsup.c (ld_options): Add entries for
>> >> >       OPTION_EXPORT_DYNAMIC_SYMBOL and
>> >> >       OPTION_EXPORT_DYNAMIC_SYMBOL_LIST.
>> >> >       (parse_args): Handle --export-dynamic-symbol and
>> >> >       --export-dynamic-symbol-list.
>> >> >       * testsuite/ld-dynamic/export-dynamic-symbol-1.d: New.
>> >> >       * testsuite/ld-dynamic/export-dynamic-symbol-2.d: New.
>> >> >       * testsuite/ld-dynamic/export-dynamic-symbol-glob.d: New.
>> >> >       * testsuite/ld-dynamic/export-dynamic-symbol-list-1.d: New.
>> >> >       * testsuite/ld-dynamic/export-dynamic-symbol-list-2.d: New.
>> >> >       * testsuite/ld-dynamic/export-dynamic-symbol-list-glob.d: New.
>> >> >       * testsuite/ld-dynamic/export-dynamic-symbol.exp: New.
>> >> >       * testsuite/ld-dynamic/export-dynamic-symbol.s: New.
>> >> >       * testsuite/ld-dynamic/foo-bar.list: New.
>> >> >       * testsuite/ld-dynamic/foo.list: New.
>> >> >       * testsuite/ld-dynamic/foo.s: New.
>> >> >       * testsuite/ld-dynamic/fstar.list: New.
>> >> >       * testsuite/ld-elf/dlempty.list: New.
>> >> >       * testsuite/ld-elf/shared.exp: Add tests for
>> >> >       --export-dynamic-symbol and --export-dynamic-symbol-list.
>> >> >---
>> >> > ld/NEWS                                       |  3 +
>> >> > ld/ld.texi                                    | 18 +++++
>> >> > ld/ldgram.y                                   |  2 +-
>> >> > ld/ldlang.c                                   | 16 ++--
>> >> > ld/ldlang.h                                   |  5 +-
>> >> > ld/ldlex.h                                    |  2 +
>> >> > ld/lexsup.c                                   | 75 +++++++++++++++++++
>> >> > .../ld-dynamic/export-dynamic-symbol-1.d      |  9 +++
>> >> > .../ld-dynamic/export-dynamic-symbol-2.d      |  9 +++
>> >> > .../ld-dynamic/export-dynamic-symbol-glob.d   |  8 ++
>> >> > .../ld-dynamic/export-dynamic-symbol-list-1.d |  9 +++
>> >> > .../ld-dynamic/export-dynamic-symbol-list-2.d |  9 +++
>> >> > .../export-dynamic-symbol-list-glob.d         |  8 ++
>> >> > .../ld-dynamic/export-dynamic-symbol.exp      | 39 ++++++++++
>> >> > .../ld-dynamic/export-dynamic-symbol.s        |  9 +++
>> >> > ld/testsuite/ld-dynamic/foo-bar.list          |  1 +
>> >> > ld/testsuite/ld-dynamic/foo.list              |  1 +
>> >> > ld/testsuite/ld-dynamic/foo.s                 |  4 +
>> >> > ld/testsuite/ld-dynamic/fstar.list            |  1 +
>> >> > ld/testsuite/ld-elf/dlempty.list              |  3 +
>> >> > ld/testsuite/ld-elf/shared.exp                | 36 +++++++++
>> >> > 21 files changed, 258 insertions(+), 9 deletions(-)
>> >> > create mode 100644 ld/testsuite/ld-dynamic/export-dynamic-symbol-1.d
>> >> > create mode 100644 ld/testsuite/ld-dynamic/export-dynamic-symbol-2.d
>> >> > create mode 100644 ld/testsuite/ld-dynamic/export-dynamic-symbol-glob.d
>> >> > create mode 100644 ld/testsuite/ld-dynamic/export-dynamic-symbol-list-1.d
>> >> > create mode 100644 ld/testsuite/ld-dynamic/export-dynamic-symbol-list-2.d
>> >> > create mode 100644 ld/testsuite/ld-dynamic/export-dynamic-symbol-list-glob.d
>> >> > create mode 100644 ld/testsuite/ld-dynamic/export-dynamic-symbol.exp
>> >> > create mode 100644 ld/testsuite/ld-dynamic/export-dynamic-symbol.s
>> >> > create mode 100644 ld/testsuite/ld-dynamic/foo-bar.list
>> >> > create mode 100644 ld/testsuite/ld-dynamic/foo.list
>> >> > create mode 100644 ld/testsuite/ld-dynamic/foo.s
>> >> > create mode 100644 ld/testsuite/ld-dynamic/fstar.list
>> >> > create mode 100644 ld/testsuite/ld-elf/dlempty.list
>> >> >
>> >> >diff --git a/ld/NEWS b/ld/NEWS
>> >> >index 9f5bbe51cf..870c480bde 100644
>> >> >--- a/ld/NEWS
>> >> >+++ b/ld/NEWS
>> >> >@@ -1,5 +1,8 @@
>> >> > -*- text -*-
>> >> >
>> >> >+* Add ELF linker command-line options, --export-dynamic-symbol and
>> >> >+  --export-dynamic-symbol-list, to make symbols dynamic.
>> >> >+
>> >> > * Add command-line options --enable-non-contiguous-regions and
>> >> >   --enable-non-contiguous-regions-warnings.
>> >> >
>> >> >diff --git a/ld/ld.texi b/ld/ld.texi
>> >> >index 4dc78e65fa..92e47c6324 100644
>> >> >--- a/ld/ld.texi
>> >> >+++ b/ld/ld.texi
>> >> >@@ -569,6 +569,24 @@ 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{glob}
>> >> >+@cindex export dynamic symbol
>> >> >+@item --export-dynamic-symbol=@var{glob}
>> >> >+When creating a dynamically linked executable, symbols matching
>> >> >+@var{glob} will be added to the dynamic symbol table. When creating a
>> >> >+shared library, references to symbols matching @var{glob} will not be
>> >> >+bound to the definitions within the shared library. This option is a
>> >> >+no-op when creating a shared library and @samp{-Bsymbolic} or
>> >> >+@samp{--dynamic-list} are not specified. This option is only meaningful
>> >> >+on ELF platforms which support shared libraries.
>> >>
>> >> Is --export-dynamic-symbol still effective for -shared?
>> >> I think either way is ok.
>> >
>> >Yes.
>> >
>> >> >+@kindex --export-dynamic-symbol-list=@var{file}
>> >> >+@cindex export dynamic symbol list
>> >> >+@item --export-dynamic-symbol-list=@var{file}
>> >> >+Specify a @samp{--export-dynamic-symbol} for each pattern in the file.
>> >> >+The format of the file is the same as the version node without
>> >> >+scope and node name.  See @ref{VERSION} for more information.
>> >> >+
>> >> > @ifclear SingleFormat
>> >> > @cindex big-endian objects
>> >> > @cindex endianness
>> >> >diff --git a/ld/ldgram.y b/ld/ldgram.y
>> >> >index df5c035c03..36845c4c30 100644
>> >> >--- a/ld/ldgram.y
>> >> >+++ b/ld/ldgram.y
>> >> >@@ -1313,7 +1313,7 @@ dynamic_list_node:
>> >> > dynamic_list_tag:
>> >> >               vers_defns ';'
>> >> >               {
>> >> >-                lang_append_dynamic_list ($1);
>> >> >+                lang_append_dynamic_list (current_dynamic_list_p, $1);
>> >> >               }
>> >> >       ;
>> >> >
>> >> >diff --git a/ld/ldlang.c b/ld/ldlang.c
>> >> >index 3d653d460d..14a6a577d2 100644
>> >> >--- a/ld/ldlang.c
>> >> >+++ b/ld/ldlang.c
>> >> >@@ -118,6 +118,7 @@ lang_statement_list_type file_chain = { NULL, NULL };
>> >> >    lang_statement_union).  */
>> >> > lang_statement_list_type input_file_chain;
>> >> > static const char *current_input_file;
>> >> >+struct bfd_elf_dynamic_list **current_dynamic_list_p;
>> >> > struct bfd_sym_chain entry_symbol = { NULL, NULL };
>> >> > const char *entry_section = ".text";
>> >> > struct lang_input_statement_flags input_flags;
>> >> >@@ -9324,15 +9325,16 @@ lang_add_unique (const char *name)
>> >> > /* Append the list of dynamic symbols to the existing one.  */
>> >> >
>> >> > void
>> >> >-lang_append_dynamic_list (struct bfd_elf_version_expr *dynamic)
>> >> >+lang_append_dynamic_list (struct bfd_elf_dynamic_list **list_p,
>> >> >+                        struct bfd_elf_version_expr *dynamic)
>> >> > {
>> >> >-  if (link_info.dynamic_list)
>> >> >+  if (*list_p)
>> >> >     {
>> >> >       struct bfd_elf_version_expr *tail;
>> >> >       for (tail = dynamic; tail->next != NULL; tail = tail->next)
>> >> >       ;
>> >> >-      tail->next = link_info.dynamic_list->head.list;
>> >> >-      link_info.dynamic_list->head.list = dynamic;
>> >> >+      tail->next = (*list_p)->head.list;
>> >> >+      (*list_p)->head.list = dynamic;
>> >> >     }
>> >> >   else
>> >> >     {
>> >> >@@ -9341,7 +9343,7 @@ lang_append_dynamic_list (struct bfd_elf_version_expr *dynamic)
>> >> >       d = (struct bfd_elf_dynamic_list *) xcalloc (1, sizeof *d);
>> >> >       d->head.list = dynamic;
>> >> >       d->match = lang_vers_match;
>> >> >-      link_info.dynamic_list = d;
>> >> >+      *list_p = d;
>> >> >     }
>> >> > }
>> >> >
>> >> >@@ -9363,7 +9365,7 @@ lang_append_dynamic_list_cpp_typeinfo (void)
>> >> >     dynamic = lang_new_vers_pattern (dynamic, symbols [i], "C++",
>> >> >                                    FALSE);
>> >> >
>> >> >-  lang_append_dynamic_list (dynamic);
>> >> >+  lang_append_dynamic_list (&link_info.dynamic_list, dynamic);
>> >> > }
>> >> >
>> >> > /* Append the list of C++ operator new and delete dynamic symbols to the
>> >> >@@ -9384,7 +9386,7 @@ lang_append_dynamic_list_cpp_new (void)
>> >> >     dynamic = lang_new_vers_pattern (dynamic, symbols [i], "C++",
>> >> >                                    FALSE);
>> >> >
>> >> >-  lang_append_dynamic_list (dynamic);
>> >> >+  lang_append_dynamic_list (&link_info.dynamic_list, dynamic);
>> >> > }
>> >> >
>> >> > /* Scan a space and/or comma separated string of features.  */
>> >> >diff --git a/ld/ldlang.h b/ld/ldlang.h
>> >> >index 3018c3e2ba..529ccd1585 100644
>> >> >--- a/ld/ldlang.h
>> >> >+++ b/ld/ldlang.h
>> >> >@@ -513,6 +513,8 @@ extern bfd_boolean entry_from_cmdline;
>> >> > extern lang_statement_list_type file_chain;
>> >> > extern lang_statement_list_type input_file_chain;
>> >> >
>> >> >+extern struct bfd_elf_dynamic_list **current_dynamic_list_p;
>> >> >+
>> >> > extern int lang_statement_iteration;
>> >> > extern struct asneeded_minfo **asneeded_list_tail;
>> >> >
>> >> >@@ -673,7 +675,8 @@ extern struct bfd_elf_version_deps *lang_add_vers_depend
>> >> >   (struct bfd_elf_version_deps *, const char *);
>> >> > extern void lang_register_vers_node
>> >> >   (const char *, struct bfd_elf_version_tree *, struct bfd_elf_version_deps *);
>> >> >-extern void lang_append_dynamic_list (struct bfd_elf_version_expr *);
>> >> >+extern void lang_append_dynamic_list (struct bfd_elf_dynamic_list **,
>> >> >+                                    struct bfd_elf_version_expr *);
>> >> > extern void lang_append_dynamic_list_cpp_typeinfo (void);
>> >> > extern void lang_append_dynamic_list_cpp_new (void);
>> >> > extern void lang_add_unique
>> >> >diff --git a/ld/ldlex.h b/ld/ldlex.h
>> >> >index 22b928d2d9..2c8d043a09 100644
>> >> >--- a/ld/ldlex.h
>> >> >+++ b/ld/ldlex.h
>> >> >@@ -81,6 +81,8 @@ enum option_values
>> >> >   OPTION_DYNAMIC_LIST_CPP_NEW,
>> >> >   OPTION_DYNAMIC_LIST_CPP_TYPEINFO,
>> >> >   OPTION_DYNAMIC_LIST_DATA,
>> >> >+  OPTION_EXPORT_DYNAMIC_SYMBOL,
>> >> >+  OPTION_EXPORT_DYNAMIC_SYMBOL_LIST,
>> >> >   OPTION_WARN_COMMON,
>> >> >   OPTION_WARN_CONSTRUCTORS,
>> >> >   OPTION_WARN_FATAL,
>> >> >diff --git a/ld/lexsup.c b/ld/lexsup.c
>> >> >index fe9526b527..2bac1631d6 100644
>> >> >--- a/ld/lexsup.c
>> >> >+++ b/ld/lexsup.c
>> >> >@@ -504,6 +504,10 @@ 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_("Export the specified symbol"), EXACTLY_TWO_DASHES },
>> >> >+  { {"export-dynamic-symbol-list", required_argument, NULL, OPTION_EXPORT_DYNAMIC_SYMBOL_LIST},
>> >> >+    '\0', N_("FILE"), N_("Read export dynamic symbol list"), EXACTLY_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},
>> >> >@@ -581,6 +585,7 @@ parse_args (unsigned argc, char **argv)
>> >> >     dynamic_list_data,
>> >> >     dynamic_list
>> >> >   } opt_dynamic_list = dynamic_list_unset;
>> >> >+  struct bfd_elf_dynamic_list *export_list = NULL;
>> >> >
>> >> >   shortopts = (char *) xmalloc (OPTION_COUNT * 3 + 2);
>> >> >   longopts = (struct option *)
>> >> >@@ -1418,6 +1423,7 @@ parse_args (unsigned argc, char **argv)
>> >> >           ldfile_open_command_file (optarg);
>> >> >           saved_script_handle = hold_script_handle;
>> >> >           parser_input = input_dynamic_list;
>> >> >+          current_dynamic_list_p = &link_info.dynamic_list;
>> >> >           yyparse ();
>> >> >         }
>> >> >         if (opt_dynamic_list != dynamic_list_data)
>> >> >@@ -1425,6 +1431,29 @@ parse_args (unsigned argc, char **argv)
>> >> >         if (opt_symbolic == symbolic)
>> >> >           opt_symbolic = symbolic_unset;
>> >> >         break;
>> >> >+      case OPTION_EXPORT_DYNAMIC_SYMBOL:
>> >> >+        {
>> >> >+          struct bfd_elf_version_expr *expr
>> >> >+            = lang_new_vers_pattern (NULL, xstrdup (optarg), NULL,
>> >> >+                                     FALSE);
>> >> >+          lang_append_dynamic_list (&export_list, expr);
>> >> >+          }
>> >> >+        break;
>> >> >+      case OPTION_EXPORT_DYNAMIC_SYMBOL_LIST:
>> >> >+        /* This option indicates a small script that only specifies
>> >> >+           an export list.  Read it, but don't assume that we've
>> >> >+           seen a linker script.  */
>> >> >+        {
>> >> >+          FILE *hold_script_handle;
>> >> >+
>> >> >+          hold_script_handle = saved_script_handle;
>> >> >+          ldfile_open_command_file (optarg);
>> >> >+          saved_script_handle = hold_script_handle;
>> >> >+          parser_input = input_dynamic_list;
>> >> >+          current_dynamic_list_p = &export_list;
>> >> >+          yyparse ();
>> >> >+        }
>> >> >+        break;
>> >> >       case OPTION_WARN_COMMON:
>> >> >         config.warn_common = TRUE;
>> >> >         break;
>> >> >@@ -1632,6 +1661,52 @@ parse_args (unsigned argc, char **argv)
>> >> >       && command_line.check_section_addresses < 0)
>> >> >     command_line.check_section_addresses = 0;
>> >> >
>> >> >+  if (export_list && !bfd_link_relocatable (&link_info))
>> >> >+    {
>> >> >+      struct bfd_elf_version_expr *head = export_list->head.list;
>> >> >+      struct bfd_elf_version_expr *next;
>> >> >+
>> >> >+      /* For --export-dynamic-symbol[-list]:
>> >> >+       1. When building executable, treat like --dynamic-list.
>> >> >+       2. When building shared object:
>> >> >+          a. If -Bsymbolic or --dynamic-list are used, treat like
>> >> >+             --dynamic-list.
>> >> >+          b. Otherwise, ignored.
>> >> >+       */
>> >> >+      bfd_boolean kept = (bfd_link_executable (&link_info)
>> >> >+                        || opt_symbolic != symbolic_unset
>> >> >+                        || opt_dynamic_list != dynamic_list_unset);
>> >> >+
>> >> >+      if (kept)
>> >> >+      {
>> >> >+        /* Append the export list to link_info.dynamic_list.  */
>> >> >+        if (link_info.dynamic_list)
>> >> >+          {
>> >> >+            for (next = head; next->next != NULL; next = next->next)
>> >> >+              ;
>> >> >+            next->next = link_info.dynamic_list->head.list;
>> >> >+            link_info.dynamic_list->head.list = head;
>> >> >+          }
>> >> >+        else
>> >> >+          link_info.dynamic_list = export_list;
>> >> >+
>> >> >+        if (opt_dynamic_list != dynamic_list_data)
>> >> >+          opt_dynamic_list = dynamic_list;
>> >> >+        if (opt_symbolic == symbolic)
>> >> >+          opt_symbolic = symbolic_unset;
>> >>
>> >> The interaction with -Bsymbolic appears to be more complex now.
>> >> I think users will pretty much avoid the combination of -Bsymbolic and
>> >> (--dynamic-list or --export-dynamic-symbol or --export-dynamic-symbol-list).
>> >>
>> >> So I beg for a re-consideration of
>> >> https://sourceware.org/bugzilla/show_bug.cgi?id=26018
>> >> https://sourceware.org/pipermail/binutils/2020-May/111223.html
>> >>
>> >
>> >Here is the updated patch on top of
>> >
>> >https://sourceware.org/pipermail/binutils/2020-May/111228.html
>>
>> Thanks for PATCH v3. LGTM.
>>
>> I have verified the semantics of new tests dl2d ~ dl2k.
>
>The updated patch to adjust ld-dynamic/export-dynamic-symbol.s
>for all ELF targets:
>
>diff --git a/ld/testsuite/ld-dynamic/export-dynamic-symbol.s
>b/ld/testsuite/ld-dynamic/export-dynamic-symbol.s
>index 4b1b8ebd5c..c55da536c5 100644
>--- a/ld/testsuite/ld-dynamic/export-dynamic-symbol.s
>+++ b/ld/testsuite/ld-dynamic/export-dynamic-symbol.s
>@@ -1,6 +1,14 @@
>   .text
>+  .global start  /* Used by SH targets.  */
>+start:
>   .global _start
> _start:
>+  .global __start
>+__start:
>+  .global main   /* Used by HPPA targets.  */
>+main:
>+  .globl   _main /* Used by LynxOS targets.  */
>+_main:
>   .word 0
>
>   .section .text.1, "ax"
>
>-- 
>H.J.

Still looks good.
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