Re: stripping symbols needed for relocations

["Jan Beulich" <JBeulich at novell dot com>]

>> The --strip-all case is out of question, but my concern is primarily
>> with the combination of --strip-symbol/--strip-symbols and -w, but
to
>> some degree also with the plain use of
--strip-symbol/--strip-symbols:
>> When trying to cut down the number of symbols in the linux kernel
>> (subject to kallsyms lookup) I'm trying to eliminate all non-text
>> symbols. Finding them is not a problem, but filtering out those used
in
>> relocations is, which is why I'd want objcopy to do this for me.
Since
>> I'm of the general opinion that --strip-symbol for symbols used in
>> relocations for non-discarded sections (which I would hope already
don't
>> get the BSF_KEEP flag set) will result in a broken output file, I'd
like
>> to make objcopy smart enough to deal with that situation (possibly
>> through a new option --keep-needed or --force-strip-needed,
depending on
>> what the desirable default would be and whether keeping the current
>> behavior is a requirement).
>
>OK - I see your point.  My original thinking was that if the user had

>specified --strip-symbol=foo on the objcopy command line then that
meant 
>that they definitely wanted "foo" stripped out, even if it was used in
a 
>reloc, and that they knew what they were doing.
>
>Given that we are dealing with the binutils here, where you are
allowed 
>to shoot yourself in the foot if you do not know what you are doing, I

>think that this behaviour of the --strip-symbol switch should be 
>retained.  I would have no objections however to a patch which added 
>another switch, say --strip-unused-symbol=<>, or indeed the 
>--keep-needed switch you suggested, in order to provide a safer 
>environment for stripping symbols.

So I chose the more fine-grained method with
--strip-unneeded-symbol[s].

Built and tested on i686-pc-linux-gnu.

Jan

binutils/
2004-12-15 Jan Beulich  <jbeulich@novell.com>

	* doc/binutils.texi: Document --strip-unneeded-symbol and
	--strip-unneeded-symbols.
	* objcopy.c (strip_unneeded_list): New.
	(enum command_line_switch): Add OPTION_STRIP_UNNEEDED_SYMBOL
	and OPTION_STRIP_UNNEEDED_SYMBOLS.
	(copy_options): Add  --strip-unneeded-symbol and
	--strip-unneeded-symbols.
	(copy_usage): Likewise.
	(filter_symbols): Suppress copying of symbol if in
strip_unneeded_list
	and the symbol is not needed.
	(copy_main): Handle OPTION_STRIP_UNNEEDED_SYMBOL and
	OPTION_STRIP_UNNEEDED_SYMBOLS.

---
/home/jbeulich/src/binutils/mainline/2004-12-03.13.35/binutils/doc/binutils.texi	2004-11-18
15:05:13.000000000 +0100
+++ 2004-12-03.13.35/binutils/doc/binutils.texi	2004-12-15
16:35:20.514605416 +0100
@@ -947,6 +947,7 @@ objcopy [@option{-F} @var{bfdname}|@opti
         [@option{-g}|@option{--strip-debug}]
         [@option{-K}
@var{symbolname}|@option{--keep-symbol=}@var{symbolname}]
         [@option{-N}
@var{symbolname}|@option{--strip-symbol=}@var{symbolname}]
+        [@option{--strip-unneeded-symbol=}@var{symbolname}]
         [@option{-G}
@var{symbolname}|@option{--keep-global-symbol=}@var{symbolname}]
         [@option{-L}
@var{symbolname}|@option{--localize-symbol=}@var{symbolname}]
         [@option{-W}
@var{symbolname}|@option{--weaken-symbol=}@var{symbolname}]
@@ -978,6 +979,7 @@ objcopy [@option{-F} @var{bfdname}|@opti
         [@option{--weaken}]
         [@option{--keep-symbols=}@var{filename}]
         [@option{--strip-symbols=}@var{filename}]
+        [@option{--strip-unneeded-symbols=}@var{filename}]
         [@option{--keep-global-symbols=}@var{filename}]
         [@option{--localize-symbols=}@var{filename}]
         [@option{--weaken-symbols=}@var{filename}]
@@ -1106,6 +1108,10 @@ be given more than once.
 Do not copy symbol @var{symbolname} from the source file.  This
option
 may be given more than once.
 
+@item --strip-unneeded-symbol=@var{symbolname}
+Do not copy symbol @var{symbolname} from the source file unless it is
needed
+by a relocation.  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
@@ -1347,6 +1353,12 @@ Apply @option{--strip-symbol} option to 
 name per line.  Line comments may be introduced by the hash
character.
 This option may be given more than once.
 
+@item --strip-unneeded-symbols=@var{filename}
+Apply @option{--strip-unneeded-symbol} option to each symbol listed
in
+the file @var{filename}.  @var{filename} is simply a flat file, with
one
+symbol name per line.  Line comments may be introduced by the hash
+character.  This option may be given more than once.
+
 @item --keep-global-symbols=@var{filename}
 Apply @option{--keep-global-symbol} option to each symbol listed in
the
 file @var{filename}.  @var{filename} is simply a flat file, with one
---
/home/jbeulich/src/binutils/mainline/2004-12-03.13.35/binutils/objcopy.c	2004-11-02
17:16:02.000000000 +0100
+++ 2004-12-03.13.35/binutils/objcopy.c	2004-12-15
16:26:32.097936960 +0100
@@ -192,6 +192,7 @@ static bfd_boolean wildcard = FALSE;
 /* List of symbols to strip, keep, localize, keep-global, weaken,
    or redefine.  */
 static struct symlist *strip_specific_list = NULL;
+static struct symlist *strip_unneeded_list = NULL;
 static struct symlist *keep_specific_list = NULL;
 static struct symlist *localize_specific_list = NULL;
 static struct symlist *keepglobal_specific_list = NULL;
@@ -231,6 +232,8 @@ enum command_line_switch
     OPTION_SREC_LEN,
     OPTION_SREC_FORCES3,
     OPTION_STRIP_SYMBOLS,
+    OPTION_STRIP_UNNEEDED_SYMBOL,
+    OPTION_STRIP_UNNEEDED_SYMBOLS,
     OPTION_KEEP_SYMBOLS,
     OPTION_LOCALIZE_SYMBOLS,
     OPTION_KEEPGLOBAL_SYMBOLS,
@@ -340,6 +343,8 @@ static struct option copy_options[] =
   {"strip-all", no_argument, 0, 'S'},
   {"strip-debug", no_argument, 0, 'g'},
   {"strip-unneeded", no_argument, 0, OPTION_STRIP_UNNEEDED},
+  {"strip-unneeded-symbol", required_argument, 0,
OPTION_STRIP_UNNEEDED_SYMBOL},
+  {"strip-unneeded-symbols", required_argument, 0,
OPTION_STRIP_UNNEEDED_SYMBOLS},
   {"strip-symbol", required_argument, 0, 'N'},
   {"strip-symbols", required_argument, 0, OPTION_STRIP_SYMBOLS},
   {"target", required_argument, 0, 'F'},
@@ -405,6 +410,9 @@ copy_usage (FILE *stream, int exit_statu
   -g --strip-debug                 Remove all debugging symbols &
sections\n\
      --strip-unneeded              Remove all symbols not needed by
relocations\n\
   -N --strip-symbol <name>         Do not copy symbol <name>\n\
+     --strip-unneeded-symbol <name>\n\
+                                   Do not copy symbol <name> unless
needed by\n\
+                                     relocations\n\
      --only-keep-debug             Strip everything but the debug
information\n\
   -K --keep-symbol <name>          Only copy symbol <name>\n\
   -L --localize-symbol <name>      Force symbol <name> to be marked as
a local\n\
@@ -443,6 +451,9 @@ copy_usage (FILE *stream, int exit_statu
      --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\
+     --strip-unneeded-symbols <file>\n\
+                                   --strip-unneeded-symbol for all
symbols listed\n\
+                                     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\
@@ -903,6 +914,10 @@ filter_symbols (bfd *abfd, bfd *obfd, as
 
       if (keep && is_specified_symbol (name, strip_specific_list))
 	keep = 0;
+      if (keep
+	  && !(flags & BSF_KEEP)
+	  && is_specified_symbol (name, strip_unneeded_list))
+	keep = 0;
       if (!keep && is_specified_symbol (name, keep_specific_list))
 	keep = 1;
       if (keep && is_strip_section (abfd, bfd_get_section (sym)))
@@ -2525,6 +2540,10 @@ copy_main (int argc, char *argv[])
 	  add_specific_symbol (optarg, &strip_specific_list);
 	  break;
 
+	case OPTION_STRIP_UNNEEDED_SYMBOL:
+	  add_specific_symbol (optarg, &strip_unneeded_list);
+	  break;
+
 	case 'L':
 	  add_specific_symbol (optarg, &localize_specific_list);
 	  break;
@@ -2858,6 +2877,10 @@ copy_main (int argc, char *argv[])
 	  add_specific_symbols (optarg, &strip_specific_list);
 	  break;
 
+	case OPTION_STRIP_UNNEEDED_SYMBOLS:
+	  add_specific_symbols (optarg, &strip_unneeded_list);
+	  break;
+
 	case OPTION_KEEP_SYMBOLS:
 	  add_specific_symbols (optarg, &keep_specific_list);
 	  break;

Attachment: binutils-mainline-strip-unneeded-symbols.patch
Description: Binary data