Change the behaviour of the --only-keep-debug option to objcopy and strip so that the sh_link and sh_info fields in stripped section headers are preserved.

bfd	* elf.c (_bfd_elf_copy_private_bfd_data): Copy the sh_link and
	sh_info fields of sections whose type has been changed to
	SHT_NOBITS.

bin	* doc/binutils.texi: Document that the --only-keep-debug option
	to strip and objcopy preserves the section headers of stripped
	sections.

tests	* binutils-all/objcopy.exp (keep_debug_symbols_and_check_links):
	New proc.  Checks that debug-info-only binaries retain the
	sh_link field in stripped sections.

4 files changed, 94 insertions, 2 deletions

diff --git a/binutils/ChangeLog b/binutils/ChangeLog
index 33c5e7d..0b5ff7f 100644
--- a/binutils/ChangeLog
+++ b/binutils/ChangeLog
@@ -1,3 +1,9 @@
+2015-08-05  Nick Clifton  <nickc@redhat.com>
+
+	* doc/binutils.texi: Document that the --only-keep-debug option
+	to strip and objcopy preserves the section headers of stripped
+	sections.
+
 2015-08-04  Yuriy M. Kaminskiy"  <yumkam@gmail.com>
 	    Tyler Hicks  <tyhicks@canonical.com>
 
diff --git a/binutils/doc/binutils.texi b/binutils/doc/binutils.texi
index 466f125..fef5f3e 100644
--- a/binutils/doc/binutils.texi
+++ b/binutils/doc/binutils.texi
@@ -1731,6 +1731,12 @@ Strip a file, removing contents of any sections that would not be
 stripped by @option{--strip-debug} and leaving the debugging sections
 intact.  In ELF files, this preserves all note sections in the output.
 
+Note - the section headers of the stripped sections are preserved,
+including their sizes, but the contents of the section are discarded.
+The section headers are preserved so that other tools can match up the
+debuginfo file with the real executable, even if that executable has
+been relocated to a different address space.
+
 The intention is that this option will be used in conjunction with
 @option{--add-gnu-debuglink} to create a two part executable.  One a
 stripped binary which will occupy less space in RAM and in a
@@ -3074,9 +3080,16 @@ When stripping a file, perhaps with @option{--strip-debug} or
 which would otherwise get stripped.
 
 @item --only-keep-debug
-Strip a file, removing contents of any sections that would not be
+Strip a file, emptying the contents of any sections that would not be
 stripped by @option{--strip-debug} and leaving the debugging sections
-intact.  In ELF files, this preserves all note sections in the output.
+intact.  In ELF files, this preserves all the note sections in the
+output as well.
+
+Note - the section headers of the stripped sections are preserved,
+including their sizes, but the contents of the section are discarded.
+The section headers are preserved so that other tools can match up the
+debuginfo file with the real executable, even if that executable has
+been relocated to a different address space.
 
 The intention is that this option will be used in conjunction with
 @option{--add-gnu-debuglink} to create a two part executable.  One a
diff --git a/binutils/testsuite/ChangeLog b/binutils/testsuite/ChangeLog
index 1076ca7..9255fb9 100644
--- a/binutils/testsuite/ChangeLog
+++ b/binutils/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2015-08-05  Nick Clifton  <nickc@redhat.com>
+
+	* binutils-all/objcopy.exp (keep_debug_symbols_and_check_links):
+	New proc.  Checks that debug-info-only binaries retain the
+	sh_link field in stripped sections.
+
 2015-08-04  Nick Clifton  <nickc@redhat.com>
 
 	* lib/utils-lib.exp (run_dump_test): Document DUMPPROG, readelf
diff --git a/binutils/testsuite/binutils-all/objcopy.exp b/binutils/testsuite/binutils-all/objcopy.exp
index ae21b22..01d2e17 100644
--- a/binutils/testsuite/binutils-all/objcopy.exp
+++ b/binutils/testsuite/binutils-all/objcopy.exp
@@ -829,12 +829,70 @@ proc keep_debug_symbols_and_test_copy { prog1 flags1 test1 prog2 flags2 test2 }
     pass $test2
 }
 
+# Tests that in a debug only copy of a file the sections
+# headers whoes types have been changed to NOBITS still
+# retain their sh_link fields.
+
+proc keep_debug_symbols_and_check_links { prog flags test } {
+    global READELF
+
+    remote_file build delete tmpdir/striprog
+    remote_download build tmpdir/copyprog tmpdir/striprog
+    if [is_remote host] {
+	set copyfile [remote_download host tmpdir/striprog]
+    } else {
+	set copyfile tmpdir/striprog
+    }
+
+    set exec_output [binutils_run $prog "$flags ${copyfile}"]
+    if ![string match "" $exec_output] {
+	fail $test
+	return
+    }
+
+    set got [binutils_run $READELF "-S --wide ${copyfile}"]
+
+    set fails 0
+    # Regexp to match a section with NOBITS type and extract its name and sh_link fields
+    while {[regexp \
+		{[^a-zA-Z]+([a-zA-Z0-9_\.]+)[ 	]+NOBITS[ 	]+[0-9a-fA-F]+ [0-9a-fA-F]+ [0-9a-fA-F]+ [0-9]+[ A]+([0-9]+)(.*)} \
+		$got all name link rest]} {
+	set sh_link 0x$link
+	if {$sh_link == 0} {
+	    # Only some NOBITS sections should have a non-zero sh_link field.
+	    # Look for them by name.
+	    verbose "NOBITS section .$name has a 0 sh_link field\n"
+	    switch $name {
+		"rela.*"	{ set fails 1 ; send_log "Expected non-zero sh_link for .$name\n" }
+		"rel.*"		{ set fails 1 ; send_log "Expected non-zero sh_link for .$name\n" }
+		"hash"		{ set fails 1 ; send_log "Expected non-zero sh_link for .$name\n" }
+		"gnu_version"	{ set fails 1 ; send_log "Expected non-zero sh_link for .$name\n" }
+		"dynsym"	{ set fails 1 ; send_log "Expected non-zero sh_link for .$name\n" }
+		"gnu.version_r"	{ set fails 1 ; send_log "Expected non-zero sh_link for .$name\n" }
+		"dynamic"	{ set fails 1 ; send_log "Expected non-zero sh_link for .$name\n" }
+		"symtab"	{ set fails 1 ; send_log "Expected non-zero sh_link for .$name\n" }
+	    }
+	}
+	set got $rest
+    }
+
+    if {$fails == 0} {
+	pass $test
+    } else {
+	fail $test
+    }
+}
+
+
 set test1 "simple objcopy of executable"
 set test2 "run objcopy of executable"
 set test3 "run stripped executable"
 set test4 "run stripped executable with saving a symbol"
 set test5 "keep only debug data"
 set test6 "simple objcopy of debug data"
+if [is_elf_format] {
+    set test7 "NOBITS sections retain sh_link field"
+}
 
 switch [copy_setup] {
     "1" {
@@ -847,6 +905,9 @@ switch [copy_setup] {
 	untested $test4
 	untested $test5
 	untested $test6
+	if [is_elf_format] {
+	    untested $test7
+	}
     }
     "3" {
 	copy_executable "$OBJCOPY" "$OBJCOPYFLAGS" "$test1" ""
@@ -855,6 +916,9 @@ switch [copy_setup] {
 	unsupported $test4
 	unsupported $test5
 	unsupported $test6
+	if [is_elf_format] {
+	    unsupported $test7
+	}
     }
     "0" {
 	copy_executable "$OBJCOPY" "$OBJCOPYFLAGS" "$test1" "$test2"
@@ -862,6 +926,9 @@ switch [copy_setup] {
 	strip_executable_with_saving_a_symbol "$STRIP" "-K main -K _main $STRIPFLAGS" "$test4"
 	keep_debug_symbols_and_test_copy "$STRIP" "--only-keep-debug $STRIPFLAGS" "$test5" \
 					 "$OBJCOPY" "$OBJCOPYFLAGS" "$test6"
+	if [is_elf_format] {
+	    keep_debug_symbols_and_check_links "$STRIP" "--only-keep-debug $STRIPFLAGS" "$test7"
+	}
     }
 }