RFC: GAS: Add option to generate unused section symbols

[Nick Clifton]

Hi Guys,

  With the 2.36 release of the binutils we stopped generating section
  symbols if they were not needed by relocations.  This helps to reduce
  object file size and enhances compatibility with the LLVM compiler.
  But I have received some bug reports about this feature, most notably
  from kernel maintainers who have found that the new behaviour breaks
  the recordmcount tool.  So I am proposing the attached patch as a
  solution.

  The patch adds an option to the assembler: --keep-unused-section-symbols=[yes|no]
  which is pretty much self describing.  The patch itself is fairly
  simple, although there is one area that might provoke comment:  Since
  the xvec structure in a BFD is accessed via a const pointer, its
  contents cannot be changed.  This makes sense most of the time, but
  poses a problem for this patch since it wants to change the
  keep_unused_section_symbols field.  So I decided that the simplest way
  to resolve this would be to allocate a new xvec structure, fill it in,
  and then change the pointer in the bfd.  This might be a bit wasteful
  of memory, but I am not expecting this feature to be used very often
  and I thought that it was better to preserve the const pointer
  semantics.

  Any comments ?

Cheers
  Nick

bfd/ChangeLog
2022-03-04  Nick Clifton  <nickc@redhat.com>

	* targets.c (bfd_set_keep_unused_section_symbols): New function.
	* bfd-in2.h: Rgenerate.

gas/ChangeLog
2022-03-04  Nick Clifton  <nickc@redhat.com>

	* as.c (keep_unused_sec_syms): New local variable.
        (parse_args): Add --keep-unused-section-symbols=[yes|no].
        (show_usage): Mention the new option.
        (main): Call bfd_set_keep_unused_section_symbols if requested.
        * doc/as.texi: Document the new option.
        * NEWS: Mention the new feature.
        * testsuite/gas/elf/unused-section-symbols.s: New source file.
        * testsuite/gas/elf/unused-section-symbols.d: New test.
        * testsuite/gas/elf/used-section-symbols.d: New test.
        * testsuite/gas/elf/elf.exp: Run the new tests.

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