[PATCH] new option for objcopy: --keep-global-symbol

[PATCH] new option for objcopy: --keep-global-symbol

[hhonda]

Hi, all.

I propose a new option for `objcopy'.

Existing options:
  -N <name>, --strip-symbol=<name>
    Strip symbol <name>.
  -K <name>, --keep-symbol=<name>
    Strip all symbols except <name>.
  -L <name>, --localize-symbol=<name>
    Localize symbol <name>.
  -W <name>, --weaken-symbol=<name>
    Weaken symbol <name>.

A new option:
  -G <name>, --keep-global-symbol=<name>
    Localize all symbols except <name>.

Furthermore, I propose a series of convenience options.
  --strip-symbols=<file>
    Apply `-N' option to each symbol listed in <file>.
  --keep-symbols=<file>
    Apply `-K' option to each symbol listed in <file>.
  --localize-symbols=<file>
    Apply `-L' option to each symbol listed in <file>.
  --keep-global-symbols=<file>
    Apply `-G' option to each symbol listed in <file>.
  --weaken-symbols=<file>
    Apply `-W' option to each symbol listed in <file>.

================================================================

The motivation of my proposal is as follows.

Suppose a source code directory tree which looks like:
    project --+-- system --+-- main.c
              |            +-- sub.c
              +-- libfoo --+-- foo1.c : foo_init(), foo_doit()
              |            +-- foo2.c : subroutine1(), subroutine2()
              +-- libbar --+-- bar1.c : bar_init(), bar_doit()
                           +-- bar2.c : subroutine1(), subroutine2()
Now look at `libfoo' directory.  It has four global symbols (foo_init,
foo_doit, subroutine1, subroutine2), but we want to export only the
former two (foo_init, foo_doit).  So we write project/libfoo/Makefile
as follows.
  all: all-in-one.o
        @
  all-in-one.o: foo1.o foo2.o
        ld -r -o all-in-one.o foo1.o foo2.o
        objcopy -G foo_init -G foo_doit all-in-one.o
If libfoo has many export symbols, we'd better write a text file
listing those symbols and use `--keep-global-symbols' option in the
Makefile.
  all-in-one.o: foo1.o foo2.o exports.txt
        ld -r -o all-in-one.o foo1.o foo2.o
        objcopy --keep-global-symbols=exports.txt all-in-one.o

If we apply the above convention for all directories (system, libfoo
and libbar), we can write the top makefile (project/Makefile)
concisely.
  DIRS := system libfoo libbar
  OBJS := $(addsuffix /all-in-one.o, $(DIRS))
  FORCEDIRS := $(addprefix force-, $(DIRS))
  a.out: $(FORCEDIRS)
        cc -o a.out $(OBJS)
  $(FORCEDIRS) : force-% : FORCE
        cd $* && $(MAKE) all
  FORCE:

================================================================

Here is a patch to binutils-2.11.

I am using the patched `objcopy' in a "--host=i686-pc-linux-gnu 
--target=mipstx39-elf32" environment, which seems to be correctly
working.

Is there any moderator who will verify and commit this patch?

HONDA Hiroki (hhonda@kobe-catv.ne.jp)

--- binutils-2.11/binutils/objcopy.c.orig	Thu Jan 18 09:17:43 2001
+++ binutils-2.11/binutils/objcopy.c	Sat May 12 16:40:50 2001
@@ -56,6 +56,7 @@ static void copy_section PARAMS ((bfd *,
 static void get_sections PARAMS ((bfd *, asection *, PTR));
 static int compare_section_lma PARAMS ((const PTR, const PTR));
 static void add_specific_symbol PARAMS ((const char *, struct symlist **));
+static void add_specific_symbols PARAMS ((const char *, struct symlist **));
 static boolean is_specified_symbol PARAMS ((const char *, struct symlist *));
 static boolean is_strip_section PARAMS ((bfd *, asection *));
 static unsigned int filter_symbols
@@ -183,11 +184,13 @@ static boolean change_leading_char = fal
 
 static boolean remove_leading_char = false;
 
-/* List of symbols to strip, keep, localize, weaken, or redefine.  */
+/* List of symbols to strip, keep, localize, keep-global, weaken,
+   or redefine.  */
 
 static struct symlist *strip_specific_list = NULL;
 static struct symlist *keep_specific_list = NULL;
 static struct symlist *localize_specific_list = NULL;
+static struct symlist *keepglobal_specific_list = NULL;
 static struct symlist *weaken_specific_list = NULL;
 static struct redefine_node *redefine_sym_list = NULL;
 
@@ -217,6 +220,11 @@ static boolean weaken = false;
 #define OPTION_REDEFINE_SYM (OPTION_WEAKEN + 1)
 #define OPTION_SREC_LEN (OPTION_REDEFINE_SYM + 1)
 #define OPTION_SREC_FORCES3 (OPTION_SREC_LEN + 1)
+#define OPTION_STRIP_SYMBOLS (OPTION_SREC_FORCES3 + 1)
+#define OPTION_KEEP_SYMBOLS (OPTION_STRIP_SYMBOLS + 1)
+#define OPTION_LOCALIZE_SYMBOLS (OPTION_KEEP_SYMBOLS + 1)
+#define OPTION_KEEPGLOBAL_SYMBOLS (OPTION_LOCALIZE_SYMBOLS + 1)
+#define OPTION_WEAKEN_SYMBOLS (OPTION_KEEPGLOBAL_SYMBOLS + 1)
 
 /* Options to handle if running as "strip".  */
 
@@ -278,6 +286,7 @@ static struct option copy_options[] =
   {"pad-to", required_argument, 0, OPTION_PAD_TO},
   {"preserve-dates", no_argument, 0, 'p'},
   {"localize-symbol", required_argument, 0, 'L'},
+  {"keep-global-symbol", required_argument, 0, 'G'},
   {"remove-leading-char", no_argument, 0, OPTION_REMOVE_LEADING_CHAR},
   {"remove-section", required_argument, 0, 'R'},
   {"set-section-flags", required_argument, 0, OPTION_SET_SECTION_FLAGS},
@@ -294,6 +303,11 @@ static struct option copy_options[] =
   {"redefine-sym", required_argument, 0, OPTION_REDEFINE_SYM},
   {"srec-len", required_argument, 0, OPTION_SREC_LEN},
   {"srec-forceS3", no_argument, 0, OPTION_SREC_FORCES3},
+  {"keep-symbols", required_argument, 0, OPTION_KEEP_SYMBOLS},
+  {"strip-symbols", required_argument, 0, OPTION_STRIP_SYMBOLS},
+  {"keep-global-symbols", required_argument, 0, OPTION_KEEPGLOBAL_SYMBOLS},
+  {"localize-symbols", required_argument, 0, OPTION_LOCALIZE_SYMBOLS},
+  {"weaken-symbols", required_argument, 0, OPTION_WEAKEN_SYMBOLS},
   {0, no_argument, 0, 0}
 };
 
@@ -335,6 +349,7 @@ copy_usage (stream, exit_status)
   -N --strip-symbol <name>         Do not copy symbol <name>\n\
   -K --keep-symbol <name>          Only copy symbol <name>\n\
   -L --localize-symbol <name>      Force symbol <name> to be marked as a local\n\
+  -G --keep-global-symbol <name>   Localize all symbols except <name>\n\
   -W --weaken-symbol <name>        Force symbol <name> to be marked as a weak\n\
      --weaken                      Force all global symbols to be marked as weak\n\
   -x --discard-all                 Remove all non-global symbols\n\
@@ -364,6 +379,11 @@ copy_usage (stream, exit_status)
      --redefine-sym <old>=<new>    Redefine symbol name <old> to <new>\n\
      --srec-len <number>           Restrict the length of generated Srecords\n\
      --srec-forceS3                Restrict the type of generated Srecords to S3\n\
+     --strip-symbols <file>        -N for all symbols listed in <file>\n\
+     --keep-symbols <file>         -K for all symbols listed in <file>\n\
+     --localize-symbols <file>     -L for all symbols listed in <file>\n\
+     --keep-global-symbols <file>  -G for all symbols listed in <file>\n\
+     --weaken-symbols <file>       -W for all symbols listed in <file>\n\
   -v --verbose                     List all object files modified\n\
   -V --version                     Display this program's version number\n\
   -h --help                        Display this output\n\
@@ -512,6 +532,43 @@ add_specific_symbol (name, list)
   *list = tmp_list;
 }
 
+/* Add symbols listed in `filename' to strip_specific_list. */
+
+static void
+add_specific_symbols (filename, list)
+     const char *filename;
+     struct symlist **list;
+{
+  struct stat st;
+  FILE *f;
+  char *p;
+  if (stat (filename, &st) < 0)
+    fatal (_("cannot stat: %s: %s"), filename, strerror (errno));
+  if (st.st_size == 0)
+    return;
+  p = (char *) xmalloc (st.st_size + 2);
+  f = fopen (filename, FOPEN_RT);
+  if (f == NULL)
+    fatal (_("cannot open: %s: %s"), filename, strerror (errno));
+  if (fread (p, 1, st.st_size, f) == 0 || ferror (f))
+    fatal (_("%s: fread failed"), filename);
+  fclose (f);
+  p[st.st_size] = '\n';
+  p[st.st_size + 1] = '\0';
+  while (p[0] != '\0')
+    {
+      int i;
+      for (i = 0; p[i] != '\n'; i++)
+	;
+      if (i != 0)
+	{
+	  p[i] = '\0';
+	  add_specific_symbol (p, list);
+	}
+      p += (i + 1);
+    }
+}
+
 /* See whether a symbol should be stripped or kept based on
    strip_specific_list and keep_symbols.  */
 
@@ -659,7 +716,9 @@ filter_symbols (abfd, obfd, osyms, isyms
 	  sym->flags |= BSF_WEAK;
 	}
       if (keep && (flags & (BSF_GLOBAL | BSF_WEAK))
-	  && is_specified_symbol (name, localize_specific_list))
+	  && (is_specified_symbol (name, localize_specific_list)
+	      || (keepglobal_specific_list != NULL
+		  && ! is_specified_symbol (name, keepglobal_specific_list))))
 	{
 	  sym->flags &= ~(BSF_GLOBAL | BSF_WEAK);
 	  sym->flags |= BSF_LOCAL;
@@ -971,6 +1030,7 @@ copy_object (ibfd, obfd)
       || strip_specific_list != NULL
       || keep_specific_list != NULL
       || localize_specific_list != NULL
+      || keepglobal_specific_list != NULL
       || weaken_specific_list != NULL
       || sections_removed
       || sections_copied
@@ -1821,7 +1881,7 @@ copy_main (argc, argv)
   struct section_list *p;
   struct stat statbuf;
 
-  while ((c = getopt_long (argc, argv, "b:i:I:j:K:N:s:O:d:F:L:R:SpgxXVvW:",
+  while ((c = getopt_long (argc, argv, "b:i:I:j:K:N:s:O:d:F:L:G:R:SpgxXVvW:",
 			   copy_options, (int *) 0)) != EOF)
     {
       switch (c)
@@ -1892,6 +1952,10 @@ copy_main (argc, argv)
 	  add_specific_symbol (optarg, &localize_specific_list);
 	  break;
 
+	case 'G':
+	  add_specific_symbol (optarg, &keepglobal_specific_list);
+	  break;
+
 	case 'W':
 	  add_specific_symbol (optarg, &weaken_specific_list);
 	  break;
@@ -2157,6 +2221,26 @@ copy_main (argc, argv)
         case OPTION_SREC_FORCES3:
 	  S3Forced = true;
           break;
+
+	case OPTION_STRIP_SYMBOLS:
+	  add_specific_symbols (optarg, &strip_specific_list);
+	  break;
+
+	case OPTION_KEEP_SYMBOLS:
+	  add_specific_symbols (optarg, &keep_specific_list);
+	  break;
+
+	case OPTION_LOCALIZE_SYMBOLS:
+	  add_specific_symbols (optarg, &localize_specific_list);
+	  break;
+
+	case OPTION_KEEPGLOBAL_SYMBOLS:
+	  add_specific_symbols (optarg, &keepglobal_specific_list);
+	  break;
+
+	case OPTION_WEAKEN_SYMBOLS:
+	  add_specific_symbols (optarg, &weaken_specific_list);
+	  break;
 
 	case 0:
 	  break;		/* we've been given a long option */
--- binutils-2.11/binutils/objcopy.1.orig	Wed Nov 29 05:40:34 2000
+++ binutils-2.11/binutils/objcopy.1	Sat May 12 16:48:20 2001
@@ -25,6 +25,7 @@
 .RB "[\|" \-\-strip\-unneeded\fR "\|]" 
 .RB "[\|" \-K\ \fIsymbolname\fR\ |\ \fB\-\-keep\-symbol=\fIsymbolname\fR "\|]" 
 .RB "[\|" \-N\ \fIsymbolname\fR\ |\ \fB\-\-strip\-symbol=\fIsymbolname\fR "\|]" 
+.RB "[\|" \-G\ \fIsymbolname\fR\ |\ \fB\-\-keep-global\-symbol=\fIsymbolname\fR "\|]" 
 .RB "[\|" \-L\ \fIsymbolname\fR\ |\ \fB\-\-localize\-symbol=\fIsymbolname\fR "\|]" 
 .RB "[\|" \-W\ \fIsymbolname\fR\ |\ \fB\-\-weaken\-symbol=\fIsymbolname\fR "\|]" 
 .RB "[\|" \-x\fR\ |\ \fB\-\-discard\-all\fR "\|]" 
@@ -51,6 +52,11 @@
 .RB "[\|" \-\-srec\-forceS3\fR "\|]"
 .RB "[\|" \-\-redefine\-sym\ \fIold=new\fR "\|]"
 .RB "[\|" \-\-weaken\fR "\|]"
+.RB "[\|" \-\-keep\-symbols=\fIfilename\fR "\|]"
+.RB "[\|" \-\-strip\-symbols=\fIfilename\fR "\|]"
+.RB "[\|" \-\-keep\-global\-symbols=\fIfilename\fR "\|]"
+.RB "[\|" \-\-localize\-symbols=\fIfilename\fR "\|]"
+.RB "[\|" \-\-weaken\-symbols=\fIfilename\fR "\|]"
 .RB "[\|" \-v\ |\ \-\-verbose\fR "\|]" 
 .RB "[\|" \-V\ |\ \-\-version\fR "\|]" 
 .RB "[\|" \-\-help\fR "\|]" 
@@ -155,6 +161,11 @@
 Do not copy symbol \fIsymbolname\fP from the source file. This option
 may be given more than once.
 .TP
+.B \-G \fIsymbolname\fR, \fB\-\-keep\-global\-symbol=\fIsymbolname
+Keep only symbol \fIsymbolname\fP global.  Make all other symbols
+local to the file, so that they are not visible externally.  This
+option may be given more than once.
+.TP
 .B \-L \fIsymbolname\fR, \fB\-\-localize\-symbol=\fIsymbolname
 Make symbol \fIsymbolname\fP local to the file, so that it is not
 visible externally.  This option may be given more than once.
@@ -299,6 +310,31 @@
 .TP
 .B \-\-weaken
 Change all global symbols in the file to be weak.
+.TP
+.B \-\-keep\-symbols=\fIfilename
+Apply \fB\-\-keep\-symbol\fP option to each symbol listed in the file
+\fIfilename\fP.  \fIfilename\fP is simply a flat file, with one symbol
+name per line.  This option may be given more than once.
+.TP
+.B \-\-strip\-symbols=\fIfilename
+Apply \fB\-\-strip\-symbol\fP option to each symbol listed in the file
+\fIfilename\fP.  \fIfilename\fP is simply a flat file, with one symbol
+name per line.  This option may be given more than once.
+.TP
+.B \-\-keep\-global\-symbols=\fIfilename
+Apply \fB\-\-keep\-global\-symbol\fP option to each symbol listed in
+the file \fIfilename\fP.  \fIfilename\fP is simply a flat file, with
+one symbol name per line.  This option may be given more than once.
+.TP
+.B \-\-localize\-symbols=\fIfilename
+Apply \fB\-\-localize\-symbol\fP option to each symbol listed in the
+file \fIfilename\fP.  \fIfilename\fP is simply a flat file, with one
+symbol name per line.  This option may be given more than once.
+.TP
+.B \-\-weaken\-symbols=\fIfilename
+Apply \fB\-\-weaken\-symbol\fP option to each symbol listed in the
+file \fIfilename\fP.  \fIfilename\fP is simply a flat file, with one
+symbol name per line.  This option may be given more than once.
 .TP
 .B \-v\fR, \fB\-\-verbose
 Verbose output: list all object files modified.  In the case of
--- binutils-2.11/binutils/binutils.texi.orig	Thu Jan 18 09:18:50 2001
+++ binutils-2.11/binutils/binutils.texi	Sat May 12 16:53:55 2001
@@ -877,6 +877,7 @@
         [ -S | --strip-all ]  [ -g | --strip-debug ]
         [ -K @var{symbolname} | --keep-symbol=@var{symbolname} ]
         [ -N @var{symbolname} | --strip-symbol=@var{symbolname} ]
+        [ -G @var{symbolname} | --keep-global-symbol=@var{symbolname} ]
         [ -L @var{symbolname} | --localize-symbol=@var{symbolname} ]
         [ -W @var{symbolname} | --weaken-symbol=@var{symbolname} ]
         [ -x | --discard-all ]  [ -X | --discard-locals ]
@@ -897,6 +898,11 @@
         [ --change-leading-char ] [ --remove-leading-char ]
         [ --srec-len=@var{ival} ] [ --srec-forceS3 ]
         [ --redefine-sym @var{old}=@var{new} ] [ --weaken ]
+        [ --keep-symbols=@var{filename} ]
+        [ --strip-symbols=@var{filename} ]
+        [ --keep-global-symbols=@var{filename} ]
+        [ --localize-symbols=@var{filename} ]
+        [ --weaken-symbols=@var{filename} ]
         [ -v | --verbose ] [ -V | --version ]  [ --help ]
         @var{infile} [@var{outfile}]
 @end smallexample
@@ -993,6 +999,12 @@
 Do not copy symbol @var{symbolname} from the source file.  This option
 may be given more than once.
 
+@item -G @var{symbolname}
+@itemx --keep-global-symbol=@var{symbolname}
+Keep only symbol @var{symbolname} global.  Make all other symbols local
+to the file, so that they are not visible externally.  This option may
+be given more than once.
+
 @item -L @var{symbolname}
 @itemx --localize-symbol=@var{symbolname}
 Make symbol @var{symbolname} local to the file, so that it is not
@@ -1175,6 +1187,31 @@
 when building an object which will be linked against other objects using
 the @code{-R} option to the linker.  This option is only effective when
 using an object file format which supports weak symbols.
+
+@item --keep-symbols=@var{filename}
+Apply @samp{--keep-symbol} option to each symbol listed in the file
+@var{filename}.  @var{filename} is simply a flat file, with one symbol
+name per line.  This option may be given more than once.
+
+@item --strip-symbols=@var{filename}
+Apply @samp{--strip-symbol} option to each symbol listed in the file
+@var{filename}.  @var{filename} is simply a flat file, with one symbol
+name per line.  This option may be given more than once.
+
+@item --keep-global-symbols=@var{filename}
+Apply @samp{--keep-global-symbol} option to each symbol listed in the
+file @var{filename}.  @var{filename} is simply a flat file, with one
+symbol name per line.  This option may be given more than once.
+
+@item --localize-symbols=@var{filename}
+Apply @samp{--localize-symbol} option to each symbol listed in the file
+@var{filename}.  @var{filename} is simply a flat file, with one symbol
+name per line.  This option may be given more than once.
+
+@item --weaken-symbols=@var{filename}
+Apply @samp{--weaken-symbol} option to each symbol listed in the file
+@var{filename}.  @var{filename} is simply a flat file, with one symbol
+name per line.  This option may be given more than once.
 
 @item -V
 @itemx --version

Re: [PATCH] new option for objcopy: --keep-global-symbol

[Nick Clifton]

Hi Honda,

  Well several people wrote in to support your idea, and nobody
  complained, so I have gone ahead and applied your patch to the
  sources.  In fact, being the nice kind of chap that I am, I also
  applied the patch to the 2.11 branch, so that when that is released
  in will be in there too.

  I made two changes to your patch.  Firstly I created an entry in the
  NEWS file mentioning this new feature.  Secondly I changed the code
  inside add_specified_symbols() so that it could cope with lines that
  are terminated by \r\n, so that it will work under Windows(tm).  I
  also added the ability to use '#' as the start of a line comment,
  because it was simple to do, and it is always a good idea to be
  able to add comments to files.

  So, thanks very much for submitting this patch, and I am sorry that
  it took so long for it to be accepted, but it got through in the end.

Cheers
	Nick

Re: [PATCH] new option for objcopy: --keep-global-symbol

[hhonda]

Hi Nick,

>                                            But people having been
> building libraries for ages, so how has this problem been solved
> before now ?

I want to know that, too.

Maybe I am so lazy that I cannot take care of prefixing
local-to-the-library symbols :->.

> Another problem that occurs to me if you strip all of the non-exported
> global symbols out the library by using this proposed patch, you will
> be forced to do this on a fully resolved binary.

???

--keep-global-symbol option leaves attributes of undefined symbols
unchanged.  So undefined symbols are kept undefined, aren't they?

>                                                   I changed the code
>  inside add_specified_symbols() so that it could cope with lines that
>  are terminated by \r\n, so that it will work under Windows(tm).

Great.

>                                                                   I
>  also added the ability to use '#' as the start of a line comment,
>  because it was simple to do, and it is always a good idea to be
>  able to add comments to files.

My add_specified_symbols() adds every non-blank line (including
comment line) to xxx_specific_list, but it causes no trouble because
valid symbols do not begin with '#' on my target machine.  I myself
use '#' comments in export.txt files and regard my
add_specified_symbols() as an example of K.I.S.S. approach, but this
again shows how lazy I am :->.

Anyway, thank you very much for accepting the patch.

HONDA Hiroki (hhonda@kobe-catv.ne.jp)

Re: [PATCH] new option for objcopy: --keep-global-symbol

[Ian Lance Taylor]

In general objcopy has a hodge-podge of options to manipulate object
files.  I don't think --keep-global-symbol is out of place in that
hodge-podge.  It might be nice to try to regularize the options, if
anybody has any clever scheme for doing so.  But in general the
ability to specify that only particular symbols be globally visible
seems reasonable.

Ian

Re: [PATCH] new option for objcopy: --keep-global-symbol

[Philip Blundell]

Hi Nick

>I am sorry but I still have serious misgivings about accepting this
>patch.  I am still open to persuasion however, and I hope that this
>email will start some discussion on the binutils list to see what
>other people think.

Well, I agree with you that this patch doesn't look like the best way to 
solve the problem at hand.  But, conversely, given that we already have
--localize-symbol and so on, it does seem to be a reasonable extension to
objcopy's existing behaviour.  So, I think we should accept the patch
regardless of the fact that it might be put to misguided use.

p.

Re: [PATCH] new option for objcopy: --keep-global-symbol

[Nick Clifton]

Hi Honda,

> > >     project --+-- system --+-- main.c
> > >               |            +-- sub.c
> > >               +-- libfoo --+-- foo1.c : foo_init(), foo_doit()
> > >               |            +-- foo2.c : subroutine1(), subroutine2()
> > >               +-- libbar --+-- bar1.c : bar_init(), bar_doit()
> > >                            +-- bar2.c : subroutine1(), subroutine2()
> > >
> > > Now look at `libfoo' directory.  It has four global symbols (foo_init,
> > > foo_doit, subroutine1, subroutine2), but we want to export only the
> > > former two (foo_init, foo_doit).
> > >
> > > [Proposal for new objcopy option to selectively 
> > >  make some symbols local].
> > 
> > I am not sure that this is such a good idea.  It would mean that
> > your library could only be built with a patched version of objcopy
> > (or a release after 2.11) which would make it less portable.
> 
> Hmm, so the question is whether or not the advantage of my proposal
> is greater than the disadvantage of portability restriction.

Well that, plus the fact that this is the first time (to my knowledge)
that a patch like this has been proposed.  But people having been
building libraries for ages, so how has this problem been solved
before now ?


> > Instead why not just prefix the local-to-the-library subroutines,
> > so that a name clash does not occur.  ie rename subroutine1() on
> > foo2.c to libfoo_subroutine1(), and so on.
> 
> Theoretically it suffices, but in practice it is inconvenient.
> 
> When libfoo has 10 files and 50 global symbols, and when we want to
> export only 5 symbols, we should prefix 45 local-to-the-library
> subroutines, which is awkward and makes the source code less readable.

Well a script could easily handle the renaming, and I seriously doubt
that a small prefix to function names would make the code less
readable.

> Or, when some of the local-to-the-library subroutines are generic
> mini-libraries (e.g. hash_lookup, lzw_decode, ...) taken from
> elsewhere, we don't want to spend tedious time renaming those
> mini-library subroutines.

Although a set of hash defines could handle that for you.


> In normal cases, we have relatively small number of export symbols
> while there are many local-to-the-library ones.  Moreover, during the
> library development, we rarely add/remove export symbols while we
> frequently add/remove local-to-the-library ones (i.e. we rarely change
> external API while we frequently change internal implementation).
> Therefore, in the Makefile, it is more convenient to specify export
> symbols than to specify local-to-the-library ones.

True, but I am suggesting that you do not do anything in the
Makefile.  You just keep your local-to-the-library functions out of
the way by prefixing them with private-to-the-library prefix.  In
fact if you are coding in C++ you can use namespaces to achieve the
same kind of effect as well.


Another problem that occurs to me if you strip all of the non-exported
global symbols out the library by using this proposed patch, you will
be forced to do this on a fully resolved binary.  Otherwise the final
link of the application will fail because there will be internal
references in the library that cannot be resolved.  But by fully
resolving the library you are forcing the application to link with the
entire library, not just those components that it uses.  This may not
be a problem for applications linking against shared libraries, but
static links in means that the application can become unnecessarily
bloated.


> An ideal solution will be to support selective specification of
> externally visible symbols not for object files but for archive files.
> However, it will require considerable amount of changes to binutils,
> and will introduce binary incompatibilities on archive file formats.
> So I propose the patch for objcopy as a second solution.
> 
> I hope you agree with me and accept the patch.

I am sorry but I still have serious misgivings about accepting this
patch.  I am still open to persuasion however, and I hope that this
email will start some discussion on the binutils list to see what
other people think.

Cheers
        Nick