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PR23611, objcopy is not removing executable relocatable sections

Alan Modra amodra@gmail.com
Mon Sep 10 04:32:00 GMT 2018 
BFD handles ELF relocation sections in an executable differently to
relocation sections in a relocatable object.  For a relocatable
object, BFD carries the relocations as data associated with the
section to which they apply; The relocation section doesn't appear as
a separate section.  For an executable, dynamic relocation sections do
appear as separate sections.  This means that objcopy needs to use
different strategies when dealing with relocations.

When --remove-relocations was added to objcopy with commit
d3e5f6c8f1e, objcopy lost the ability to remove dynamic relocation
sections such as .rela.plt from executables using the option
"--remove-section=.rela.plt".  This patch reinstates that
functionality.

I thought it best to keep --remove-relocations as is, rather than
extending to handle dynamic relocations as per the patch in the PR,
because executables linked with --emit-relocs may have both dynamic
and non-dynamic relocations.  In that case --remove-relocataions=* is
useful to remove all the non-dynamic relocations.

	PR binutils/23611
	* objcopy.c (handle_remove_section_option): Consider .rela and
	.rel sections for stripping directly as well as attached to the
	associated section they relocate.
	* doc/binutils.texi (remove-relocations): Specify that this
	option removes non-dynamic relocation sections.
	* testsuite/binutils-all/objcopy.exp
	(objcopy_remove_relocations_from_executable): New test.

diff --git a/binutils/doc/binutils.texi b/binutils/doc/binutils.texi
index e40ccb073d..76cbed05af 100644
--- a/binutils/doc/binutils.texi
+++ b/binutils/doc/binutils.texi
@@ -1321,17 +1321,20 @@ will remove all sections matching the pattern '.text.*', but will not
 remove the section '.text.foo'.
 
 @item --remove-relocations=@var{sectionpattern}
-Remove relocations from the output file for any section matching
-@var{sectionpattern}.  This option may be given more than once.  Note
-that using this option inappropriately may make the output file
-unusable.  Wildcard characters are accepted in @var{sectionpattern}.
+Remove non-dynamic relocations from the output file for any section
+matching @var{sectionpattern}.  This option may be given more than
+once.  Note that using this option inappropriately may make the output
+file unusable, and attempting to remove a dynamic relocation section
+such as @samp{.rela.plt} from an executable or shared library with
+@option{--remove-relocations=.plt} will not work.  Wildcard characters
+are accepted in @var{sectionpattern}.
 For example:
 
 @smallexample
   --remove-relocations=.text.*
 @end smallexample
 
-will remove the relocations for all sections matching the patter
+will remove the relocations for all sections matching the pattern
 '.text.*'.
 
 If the first character of @var{sectionpattern} is the exclamation
diff --git a/binutils/objcopy.c b/binutils/objcopy.c
index 6bd933993b..f712ffe591 100644
--- a/binutils/objcopy.c
+++ b/binutils/objcopy.c
@@ -3943,7 +3943,7 @@ discard_relocations (bfd *ibfd ATTRIBUTE_UNUSED, asection *isection)
 /* 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.  */
+   be done using a different technique in a relocatable object.  */
 
 static void
 handle_remove_section_option (const char *section_pattern)
@@ -3952,11 +3952,9 @@ handle_remove_section_option (const char *section_pattern)
     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;
-    }
+
+  find_section_list (section_pattern, TRUE, SECTION_CONTEXT_REMOVE);
+  sections_removed = TRUE;
 }
 
 /* Copy relocations in input section ISECTION of IBFD to an output
diff --git a/binutils/testsuite/binutils-all/objcopy.exp b/binutils/testsuite/binutils-all/objcopy.exp
index d979648758..61793d98f5 100644
--- a/binutils/testsuite/binutils-all/objcopy.exp
+++ b/binutils/testsuite/binutils-all/objcopy.exp
@@ -1223,3 +1223,36 @@ proc objcopy_test_without_global_symbol { } {
 setup_xfail aarch64*-*-* arm*-*-*
 
 objcopy_test_without_global_symbol
+
+# objcopy remove relocation from executable test
+
+proc objcopy_remove_relocations_from_executable { } {
+    global OBJCOPY
+    global srcdir
+    global subdir
+    global READELF
+
+    set test "remove-section relocation sections"
+
+    if { [target_compile $srcdir/$subdir/testprog.c tmpdir/pr23611 executable debug] != "" } {
+	untested $test
+	return
+    }
+
+    if [is_remote host] {
+	set objfile [remote_download host tmpdir/pr23611]
+    } else {
+	set objfile tmpdir/pr23611
+    }
+    set out tmpdir/pr23611.out
+
+    set exec_output1 [binutils_run $OBJCOPY "-R .rela.plt -R .rela.dyn -R .rel.plt -R .rel.dyn $objfile $out"]
+    set exec_output2 [binutils_run $READELF "-S $out"]
+    if { [string match "*.rel.plt*" $exec_output2] || [string match "*.rela.plt*" $exec_output2] || [string match "*.rel.dyn*" $exec_output2] || [string match "*.rela.dyn*" $exec_output2] } {
+	fail $test
+	return
+    }
+    pass $test
+}
+
+objcopy_remove_relocations_from_executable

-- 
Alan Modra
Australia Development Lab, IBM
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