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.

1 files changed, 31 insertions, 2 deletions

diff --git a/binutils/objcopy.c b/binutils/objcopy.c
index 4140077..206d80b 100644
--- a/binutils/objcopy.c
+++ b/binutils/objcopy.c
@@ -97,6 +97,7 @@ static int deterministic = -1;		/* Enable deterministic archives.  */
 static int status = 0;			/* Exit status.  */
 
 static bool    merge_notes = false;	/* Merge note sections.  */
+static bool strip_section_headers = false;/* Strip section headers.  */
 
 typedef struct merged_note_section
 {
@@ -365,6 +366,7 @@ enum command_line_switch
   OPTION_SREC_LEN,
   OPTION_STACK,
   OPTION_STRIP_DWO,
+  OPTION_STRIP_SECTION_HEADERS,
   OPTION_STRIP_SYMBOLS,
   OPTION_STRIP_UNNEEDED,
   OPTION_STRIP_UNNEEDED_SYMBOL,
@@ -403,6 +405,7 @@ static struct option strip_options[] =
   {"preserve-dates", no_argument, 0, 'p'},
   {"remove-section", required_argument, 0, 'R'},
   {"remove-relocations", required_argument, 0, OPTION_REMOVE_RELOCS},
+  {"strip-section-headers", no_argument, 0, OPTION_STRIP_SECTION_HEADERS},
   {"strip-all", no_argument, 0, 's'},
   {"strip-debug", no_argument, 0, 'S'},
   {"strip-dwo", no_argument, 0, OPTION_STRIP_DWO},
@@ -492,6 +495,7 @@ static struct option copy_options[] =
   {"remove-leading-char", no_argument, 0, OPTION_REMOVE_LEADING_CHAR},
   {"remove-section", required_argument, 0, 'R'},
   {"remove-relocations", required_argument, 0, OPTION_REMOVE_RELOCS},
+  {"strip-section-headers", no_argument, 0, OPTION_STRIP_SECTION_HEADERS},
   {"rename-section", required_argument, 0, OPTION_RENAME_SECTION},
   {"reverse-bytes", required_argument, 0, OPTION_REVERSE_BYTES},
   {"section-alignment", required_argument, 0, OPTION_PE_SECTION_ALIGNMENT},
@@ -592,6 +596,7 @@ copy_usage (FILE *stream, int exit_status)
      --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\
+     --strip-section-headers              Strip section header from the output\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\
@@ -730,6 +735,7 @@ strip_usage (FILE *stream, int exit_status)
   fprintf (stream, _("\
   -R --remove-section=<name>       Also remove section <name> from the output\n\
      --remove-relocations <name>   Remove relocations from section <name>\n\
+     --strip-section-headers       Strip section headers from the output\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\
@@ -2695,7 +2701,16 @@ copy_object (bfd *ibfd, bfd *obfd, const bfd_arch_info_type *input_arch)
      necessary.  */
   VerilogDataEndianness = ibfd->xvec->byteorder;
 
-  if (bfd_get_flavour (ibfd) != bfd_target_elf_flavour)
+  if (bfd_get_flavour (ibfd) == bfd_target_elf_flavour)
+    {
+      if (strip_section_headers)
+	{
+	  ibfd->flags |= BFD_NO_SECTION_HEADER;
+	  strip_symbols = STRIP_ALL;
+	  merge_notes = true;
+	}
+    }
+  else
     {
       if ((do_debug_sections & compress) != 0
 	  && do_debug_sections != compress)
@@ -2712,6 +2727,13 @@ copy_object (bfd *ibfd, bfd *obfd, const bfd_arch_info_type *input_arch)
 		     bfd_get_archive_filename (ibfd));
 	  return false;
 	}
+
+      if (strip_section_headers)
+	{
+	  non_fatal (_("--strip_section_headers is unsupported on `%s'"),
+		     bfd_get_archive_filename (ibfd));
+	  return false;
+	}
     }
 
   if (verbose)
@@ -3456,7 +3478,7 @@ copy_object (bfd *ibfd, bfd *obfd, const bfd_arch_info_type *input_arch)
 	  free (merged);
 	}
     }
-  else if (merge_notes && ! is_strip)
+  else if (merge_notes && ! is_strip && ! strip_section_headers)
     non_fatal (_("%s: Could not find any mergeable note sections"),
 	       bfd_get_filename (ibfd));
 
@@ -4759,6 +4781,9 @@ strip_main (int argc, char *argv[])
 	case OPTION_REMOVE_RELOCS:
 	  handle_remove_relocations_option (optarg);
 	  break;
+	case OPTION_STRIP_SECTION_HEADERS:
+	  strip_section_headers = true;
+	  break;
 	case 's':
 	  strip_symbols = STRIP_ALL;
 	  break;
@@ -5228,6 +5253,10 @@ copy_main (int argc, char *argv[])
 	  handle_remove_relocations_option (optarg);
 	  break;
 
+	case OPTION_STRIP_SECTION_HEADERS:
+	  strip_section_headers = true;
+	  break;
+
 	case 'S':
 	  strip_symbols = STRIP_ALL;
 	  break;