ELF: Strip section header in ELF objects

Section header isn't mandatory on ELF executable nor shared library.
This patch adds a new linker option, -z nosectionheader, to omit ELF
section header, a new objcopy and strip option, --strip-section-headers,
to remove ELF section headers.

bfd/

2023-06-06  H.J. Lu  <hongjiu.lu@intel.com>
	    Kaylee Blake  <klkblake@gmail.com>

	PR ld/25617
	* bfd.c (BFD_NO_SECTION_HEADER): New.
	(BFD_FLAGS_SAVED): Add BFD_NO_SECTION_HEADER.
	(BFD_FLAGS_FOR_BFD_USE_MASK): Likewise.
	* elfcode.h (elf_swap_ehdr_out): Omit section header with
	BFD_NO_SECTION_HEADER.
	(elf_write_shdrs_and_ehdr): Likewise.
	* elfxx-target.h (TARGET_BIG_SYM): Add BFD_NO_SECTION_HEADER
	to object_flags.
	(TARGET_LITTLE_SYM): Likewise.
	* bfd-in2.h: Regenerated.

binutils/

2023-06-06  H.J. Lu  <hongjiu.lu@intel.com>

	PR ld/25617
	* NEWS: Mention --strip-section-headers for objcopy and strip.
	* objcopy.c (strip_section_headers): New.
	(command_line_switch): Add OPTION_STRIP_SECTION_HEADERS.
	(strip_options): Add --strip-section-headers.
	(copy_options): Likewise.
	(copy_usage): Add --strip-section-headers.
	(strip_usage): Likewise.
	(copy_object): Handle --strip-section-headers for ELF files.
	(strip_main): Handle OPTION_STRIP_SECTION_HEADERS.
	(copy_main): Likewise.
	* doc/binutils.texi: Document --strip-section-headers for objcopy
	and strip.

ld/

2023-06-06  H.J. Lu  <hongjiu.lu@intel.com>
	    Kaylee Blake  <klkblake@gmail.com>

	PR ld/25617
	* NEWS: Mention -z nosectionheader.
	* emultempl/elf.em: Support -z sectionheader and
	-z nosectionheader.
	* ld.h (ld_config_type): Add no_section_header.
	* ld.texi: Document -z sectionheader and -z nosectionheader.
	* ldlang.c (ldlang_open_output): Handle
	config.no_section_header.
	* lexsup.c (parse_args): Enable --strip-all with
	-z nosectionheader.  Disallow -r with -z nosectionheader.
	(elf_static_list_options): Add -z sectionheader and
	-z nosectionheader.

6 files changed, 32 insertions, 0 deletions

diff --git a/ld/NEWS b/ld/NEWS
index 4dee230..dbeea12 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -15,6 +15,9 @@
 * The linker script syntax has a new command for output sections: ASCIZ "string"
   This will insert a zero-terminated string at the current location.
 
+* Add command-line option, -z nosectionheader, to omit ELF section
+  header.
+
 Changes in 2.40:
 
 * The linker has a new command line option to suppress the generation of any
diff --git a/ld/emultempl/elf.em b/ld/emultempl/elf.em
index e367299..3f67f8b 100644
--- a/ld/emultempl/elf.em
+++ b/ld/emultempl/elf.em
@@ -807,6 +807,10 @@ fragment <<EOF
 		     "must be default, internal, hidden, or protected"),
 		   optarg);
 	}
+      else if (strcmp (optarg, "sectionheader") == 0)
+	config.no_section_header = false;
+      else if (strcmp (optarg, "nosectionheader") == 0)
+	config.no_section_header = true;
 EOF
 
 if test x"$GENERATE_SHLIB_SCRIPT" = xyes; then
diff --git a/ld/ld.h b/ld/ld.h
index 1882a28..a0f8a15 100644
--- a/ld/ld.h
+++ b/ld/ld.h
@@ -280,6 +280,9 @@ typedef struct
   /* If set, code and non-code sections should never be in one segment.  */
   bool separate_code;
 
+  /* If set, generation of ELF section header should be suppressed.  */
+  bool no_section_header;
+
   /* The rpath separation character.  Usually ':'.  */
   char rpath_separator;
 
diff --git a/ld/ld.texi b/ld/ld.texi
index a007ae7..aa8b1aa 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -1544,6 +1544,11 @@ Don't create an ELF @code{PT_GNU_RELRO} segment if @samp{norelro}.
 Report dynamic relative relocations generated by linker.  Supported for
 Linux/i386 and Linux/x86_64.
 
+@item sectionheader
+@itemx nosectionheader
+Generate section header.  Don't generate section header if
+@samp{nosectionheader} is used.  @option{sectionheader} is the default.
+
 @item separate-code
 @itemx noseparate-code
 Create separate code @code{PT_LOAD} segment header in the object.  This
diff --git a/ld/ldlang.c b/ld/ldlang.c
index e359a89..f4a8b72 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -3434,6 +3434,10 @@ ldlang_open_output (lang_statement_union_type *statement)
 	link_info.output_bfd->flags |= BFD_TRADITIONAL_FORMAT;
       else
 	link_info.output_bfd->flags &= ~BFD_TRADITIONAL_FORMAT;
+      if (config.no_section_header)
+	link_info.output_bfd->flags |= BFD_NO_SECTION_HEADER;
+      else
+	link_info.output_bfd->flags &= ~BFD_NO_SECTION_HEADER;
       break;
 
     case lang_target_statement_enum:
diff --git a/ld/lexsup.c b/ld/lexsup.c
index 4e20e93..fe87223 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -1998,6 +1998,15 @@ parse_args (unsigned argc, char **argv)
 	break;
       }
 
+  /* -z nosectionheader implies --strip-all.  */
+  if (config.no_section_header)
+    {
+      if (bfd_link_relocatable (&link_info))
+	einfo (_("%F%P: -r and -z nosectionheader may not be used together\n"));
+
+      link_info.strip = strip_all;
+    }
+
   if (!bfd_link_dll (&link_info))
     {
       if (command_line.filter_shlib)
@@ -2272,6 +2281,10 @@ elf_static_list_options (FILE *file)
   fprintf (file, _("\
   -z start-stop-visibility=V  Set visibility of built-in __start/__stop symbols\n\
                                 to DEFAULT, PROTECTED, HIDDEN or INTERNAL\n"));
+  fprintf (file, _("\
+  -z sectionheader            Generate section header (default)\n"));
+  fprintf (file, _("\
+  -z nosectionheader          Do not generate section header\n"));
 }
 
 static void