objcopy/strip: Add option --remove-relocations=SECTIONPATTERN

The objcopy and strip tools make use of the bfd library to manipulate
the state of the input file (to produce an output file).  Within the
input file (for ELF at least), relocations are held within a section,
and so, if the user wanted to remove the relocations, but keep the
section to which the relocations would have been applied, it is tempting
to think that specifying the name of a relocation section to objcopy's
--remove-section option might do what you want, for example:

   objcopy --remove-section=.rela.text input.elf output.elf

However, this does not work.  The reason is that when the input file is
loaded, relocations are not managed as sections, but are, instead,
loaded as data associated with the section to which the relocations
would be applied.  In our example above the relocations in '.rela.text'
are held as data on the section '.text' once 'input.elf' is loaded.

One task that objcopy and strip do is copy the relocations from the
input file to the output file if the section is also being copied from
the input file to the output file.

This commit adds a new command line option for objcopy and strip,
--remove-relocations, which can be used to remove the relocations, while
keeping the section that the relocations would have been applied to, for
example:

    objcopy --remove-relocations=.text input.elf output.elf

in this case the section '.text' will appear in both 'input.elf' and
'output.elf', but any relocations in 'input.elf' that apply to '.text'
will not be present in 'output.elf'.

I have also added a special case to the handling of --remove-section
that spots if a user tries to remove a relocation section (currently
this is done by spotting the '.rela.' or '.rel.' prefix) and forwards
the request to --remove-relocations.

As with --remove-section and --only-section the --remove-relocations
option supports the '!' prefix on the section-patterns it takes to allow
for sections to be specifically not matched.

There are tests for all the new functionality.

binutils/ChangeLog:

	* doc/binutils.texi (objcopy): Document 'remove-relocations'.
	(strip): Likewise.
	* objcopy.c (SECTION_CONTEXT_REMOVE_RELOCS): Define.
	(enum command_line_switch): Add 'OPTION_REMOVE_RELOCS'.
	(struct option strip_options): Add 'remove-relocations'.
	(struct option copy_options): Likewise.
	(copy_usage): Likewise.
	(strip_usage): Likewise.
	(handle_remove_relocations_option): New function.
	(discard_relocations): New function.
	(handle_remove_section_option): New function.
	(copy_relocations_in_section): Use discard_relocations.
	(strip_main): Use handle_remove_section_option for
	'remove-section', and handle 'remove-relocations' option.
	(copy_main): Likewise.
	* testsuite/binutils-all/objcopy.exp: Run new tests.
	* testsuite/binutils-all/remove-relocs-01.d: New file.
	* testsuite/binutils-all/remove-relocs-01.s: New file.
	* testsuite/binutils-all/remove-relocs-02.d: New file.
	* testsuite/binutils-all/remove-relocs-03.d: New file.
	* testsuite/binutils-all/remove-relocs-04.d: New file.
	* testsuite/binutils-all/remove-relocs-05.d: New file.
	* testsuite/binutils-all/remove-relocs-06.d: New file.

1 files changed, 58 insertions, 5 deletions

diff --git a/binutils/objcopy.c b/binutils/objcopy.c
index 41ccc76..cf3f983 100644
--- a/binutils/objcopy.c
+++ b/binutils/objcopy.c
@@ -139,6 +139,7 @@ struct section_list
 #define SECTION_CONTEXT_SET_LMA   (1 << 4) /* Set the sections' LMA address.  */
 #define SECTION_CONTEXT_ALTER_LMA (1 << 5) /* Increment or decrement the section's LMA address.  */
 #define SECTION_CONTEXT_SET_FLAGS (1 << 6) /* Set the section's flags.  */
+#define SECTION_CONTEXT_REMOVE_RELOCS (1 << 7) /* Remove relocations for this section.  */
 
   bfd_vma		vma_val;   /* Amount to change by or set to.  */
   bfd_vma		lma_val;   /* Amount to change by or set to.  */
@@ -326,6 +327,7 @@ enum command_line_switch
   OPTION_REDEFINE_SYM,
   OPTION_REDEFINE_SYMS,
   OPTION_REMOVE_LEADING_CHAR,
+  OPTION_REMOVE_RELOCS,
   OPTION_RENAME_SECTION,
   OPTION_REVERSE_BYTES,
   OPTION_SECTION_ALIGNMENT,
@@ -367,6 +369,7 @@ static struct option strip_options[] =
   {"output-target", required_argument, 0, 'O'},
   {"preserve-dates", no_argument, 0, 'p'},
   {"remove-section", required_argument, 0, 'R'},
+  {"remove-relocations", required_argument, 0, OPTION_REMOVE_RELOCS},
   {"strip-all", no_argument, 0, 's'},
   {"strip-debug", no_argument, 0, 'S'},
   {"strip-dwo", no_argument, 0, OPTION_STRIP_DWO},
@@ -451,6 +454,7 @@ static struct option copy_options[] =
   {"redefine-syms", required_argument, 0, OPTION_REDEFINE_SYMS},
   {"remove-leading-char", no_argument, 0, OPTION_REMOVE_LEADING_CHAR},
   {"remove-section", required_argument, 0, 'R'},
+  {"remove-relocations", required_argument, 0, OPTION_REMOVE_RELOCS},
   {"rename-section", required_argument, 0, OPTION_RENAME_SECTION},
   {"reverse-bytes", required_argument, 0, OPTION_REVERSE_BYTES},
   {"section-alignment", required_argument, 0, OPTION_SECTION_ALIGNMENT},
@@ -538,6 +542,7 @@ copy_usage (FILE *stream, int exit_status)
   -j --only-section <name>         Only copy section <name> into the output\n\
      --add-gnu-debuglink=<file>    Add section .gnu_debuglink linking to <file>\n\
   -R --remove-section <name>       Remove section <name> from the output\n\
+     --remove-relocations <name>   Remove relocations from section <name>\n\
   -S --strip-all                   Remove all symbol and relocation information\n\
   -g --strip-debug                 Remove all debugging symbols & sections\n\
      --strip-dwo                   Remove all DWO sections\n\
@@ -668,6 +673,7 @@ strip_usage (FILE *stream, int exit_status)
                                    Disable -D behavior (default)\n"));
   fprintf (stream, _("\
   -R --remove-section=<name>       Also remove section <name> from the output\n\
+     --remove-relocations <name>   Remove relocations from section <name>\n\
   -s --strip-all                   Remove all symbol and relocation information\n\
   -g -S -d --strip-debug           Remove all debugging symbols & sections\n\
      --strip-dwo                   Remove all DWO sections\n\
@@ -3207,6 +3213,46 @@ skip_section (bfd *ibfd, sec_ptr isection)
   return FALSE;
 }
 
+/* Add section SECTION_PATTERN to the list of sections that will have their
+   relocations removed.  */
+
+static void
+handle_remove_relocations_option (const char *section_pattern)
+{
+  find_section_list (section_pattern, TRUE, SECTION_CONTEXT_REMOVE_RELOCS);
+}
+
+/* Return TRUE if ISECTION from IBFD should have its relocations removed,
+   otherwise return FALSE.  If the user has requested that relocations be
+   removed from a section that does not have relocations then this
+   function will still return TRUE.  */
+
+static bfd_boolean
+discard_relocations (bfd *ibfd ATTRIBUTE_UNUSED, asection *isection)
+{
+  return (find_section_list (bfd_section_name (ibfd, isection), FALSE,
+			     SECTION_CONTEXT_REMOVE_RELOCS) != NULL);
+}
+
+/* Wrapper for dealing with --remove-section (-R) command line arguments.
+   A special case is detected here, if the user asks to remove a relocation
+   section (one starting with ".rela." or ".rel.") then this removal must
+   be done using a different technique.  */
+
+static void
+handle_remove_section_option (const char *section_pattern)
+{
+  if (strncmp (section_pattern, ".rela.", 6) == 0)
+    handle_remove_relocations_option (section_pattern + 5);
+  else if (strncmp (section_pattern, ".rel.", 5) == 0)
+    handle_remove_relocations_option (section_pattern + 4);
+  else
+    {
+      find_section_list (section_pattern, TRUE, SECTION_CONTEXT_REMOVE);
+      sections_removed = TRUE;
+    }
+}
+
 /* Copy relocations in input section ISECTION of IBFD to an output
    section with the same name in OBFDARG.  If stripping then don't
    copy any relocation info.  */
@@ -3226,7 +3272,9 @@ copy_relocations_in_section (bfd *ibfd, sec_ptr isection, void *obfdarg)
   osection = isection->output_section;
 
   /* Core files and DWO files do not need to be relocated.  */
-  if (bfd_get_format (obfd) == bfd_core || strip_symbols == STRIP_NONDWO)
+  if (bfd_get_format (obfd) == bfd_core
+      || strip_symbols == STRIP_NONDWO
+      || discard_relocations (ibfd, isection))
     relsize = 0;
   else
     {
@@ -3606,8 +3654,10 @@ strip_main (int argc, char *argv[])
 	  input_target = output_target = optarg;
 	  break;
 	case 'R':
-	  find_section_list (optarg, TRUE, SECTION_CONTEXT_REMOVE);
-	  sections_removed = TRUE;
+	  handle_remove_section_option (optarg);
+	  break;
+	case OPTION_REMOVE_RELOCS:
+	  handle_remove_relocations_option (optarg);
 	  break;
 	case 's':
 	  strip_symbols = STRIP_ALL;
@@ -4009,8 +4059,11 @@ copy_main (int argc, char *argv[])
 	  break;
 
 	case 'R':
-	  find_section_list (optarg, TRUE, SECTION_CONTEXT_REMOVE);
-	  sections_removed = TRUE;
+	  handle_remove_section_option (optarg);
+	  break;
+
+        case OPTION_REMOVE_RELOCS:
+	  handle_remove_relocations_option (optarg);
 	  break;
 
 	case 'S':