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, 26 insertions, 10 deletions

diff --git a/bfd/elfcode.h b/bfd/elfcode.h
index e4e29f0..495e498 100644
--- a/bfd/elfcode.h
+++ b/bfd/elfcode.h
@@ -266,6 +266,7 @@ elf_swap_ehdr_out (bfd *abfd,
 {
   unsigned int tmp;
   int signed_vma = get_elf_backend_data (abfd)->sign_extend_vma;
+  bool no_section_header = (abfd->flags & BFD_NO_SECTION_HEADER) != 0;
   memcpy (dst->e_ident, src->e_ident, EI_NIDENT);
   /* note that all elements of dst are *arrays of unsigned char* already...  */
   H_PUT_16 (abfd, src->e_type, dst->e_type);
@@ -276,7 +277,10 @@ elf_swap_ehdr_out (bfd *abfd,
   else
     H_PUT_WORD (abfd, src->e_entry, dst->e_entry);
   H_PUT_WORD (abfd, src->e_phoff, dst->e_phoff);
-  H_PUT_WORD (abfd, src->e_shoff, dst->e_shoff);
+  if (no_section_header)
+    H_PUT_WORD (abfd, 0, dst->e_shoff);
+  else
+    H_PUT_WORD (abfd, src->e_shoff, dst->e_shoff);
   H_PUT_32 (abfd, src->e_flags, dst->e_flags);
   H_PUT_16 (abfd, src->e_ehsize, dst->e_ehsize);
   H_PUT_16 (abfd, src->e_phentsize, dst->e_phentsize);
@@ -284,15 +288,24 @@ elf_swap_ehdr_out (bfd *abfd,
   if (tmp > PN_XNUM)
     tmp = PN_XNUM;
   H_PUT_16 (abfd, tmp, dst->e_phnum);
-  H_PUT_16 (abfd, src->e_shentsize, dst->e_shentsize);
-  tmp = src->e_shnum;
-  if (tmp >= (SHN_LORESERVE & 0xffff))
-    tmp = SHN_UNDEF;
-  H_PUT_16 (abfd, tmp, dst->e_shnum);
-  tmp = src->e_shstrndx;
-  if (tmp >= (SHN_LORESERVE & 0xffff))
-    tmp = SHN_XINDEX & 0xffff;
-  H_PUT_16 (abfd, tmp, dst->e_shstrndx);
+  if (no_section_header)
+    {
+      H_PUT_16 (abfd, 0, dst->e_shentsize);
+      H_PUT_16 (abfd, 0, dst->e_shnum);
+      H_PUT_16 (abfd, 0, dst->e_shstrndx);
+    }
+  else
+    {
+      H_PUT_16 (abfd, src->e_shentsize, dst->e_shentsize);
+      tmp = src->e_shnum;
+      if (tmp >= (SHN_LORESERVE & 0xffff))
+	tmp = SHN_UNDEF;
+      H_PUT_16 (abfd, tmp, dst->e_shnum);
+      tmp = src->e_shstrndx;
+      if (tmp >= (SHN_LORESERVE & 0xffff))
+	tmp = SHN_XINDEX & 0xffff;
+      H_PUT_16 (abfd, tmp, dst->e_shstrndx);
+    }
 }
 
 /* Translate an ELF section header table entry in external format into an
@@ -1077,6 +1090,9 @@ elf_write_shdrs_and_ehdr (bfd *abfd)
       || bfd_bwrite (&x_ehdr, amt, abfd) != amt)
     return false;
 
+  if ((abfd->flags & BFD_NO_SECTION_HEADER) != 0)
+    return true;
+
   /* Some fields in the first section header handle overflow of ehdr
      fields.  */
   if (i_ehdrp->e_phnum >= PN_XNUM)