[Morello] Capability data relocations

[Morello] Capability data relocations

Introduce three new relocations disguised as two relocations to
support capabilities.

R_MORELLO_CAPINIT is emitted as a static relocation by the assembler
and as a dynamic relocation by the linker; it's a one on one free!

The R_MORELLO_CAPINIT static relocation is emitted by the assembler to
provide capability information to the static linker.  The static
linker may do one of two things:

- For local symbols that can be resolved at link time, the static
  linker sets up frag and emits a R_MORELLO_RELATIVE dynamic
  relocation that the dynamic linker can resolve in a manner similar
  to R_AARCH64_RELATIVE.  The dynamic linker will have all of the
  information it needs (i.e. permissions, size and relative address)
  to set up the capability without needing to peek into the symbol
  table.

- For dynamic symbols, the static linker emits a R_MORELLO_CAPINIT
  with the reference of the dynamic symbol it refers to.  The dynamic
  linker is then responsible for resolving the symbol at runtime and
  setting up the capability based on the properties of the symbol it
  is able to deduce.

Linker and Linker script defined symbols
----------------------------------------

For symbols defined by the linker or in linker scripts, capability
size and permissions are based on the section the symbol belongs to.

For linker defined symbols (i.e. _DYNAMIC or _GLOBAL_OFFSET_TABLE_)
this is straightforward since the linker puts them in the correct
section and at the start.

For symbols defined in the linker script, if they are anywhere but the
end of the output script definition, their range becomes the point at
which they are defined, up to the end of the output section.  For
symbols defined at the end of the output section, the symbols are
defined with a zero size unless their name is of the form __start_.*
or __.*_start, indicating a start of the section that follows it.  In
this case, the symbols are given the range and permission of the
output section following it.

Ideally, the last case (i.e. the heuristic looking for the name)
should be strictly for compatibility and should eventually be fixed in
the linker script to put the symbol into the output section it intends
to track.  It may be a useful enhancement to add a warning to that
effect.

bfd/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* elfnn-aarch64.c (elfNN_aarch64_howto_table,
	elfNN_aarch64_final_link_relocate, elfNN_aarch64_check_relocs,
	elfNN_aarch64_relocate_section): Add R_MORELLO_CAPINIT and
	R_MORELLO_RELATIVE.
	(elf_aarch64_link_hash_table): New member srelcaps.
	(c64_valid_cap_range, exponent, cap_meta,
	section_start_symbol, c64_fixup_frag): New functions.
	* elfxx-aarch64.c (_bfd_aarch64_elf_put_addend,
	_bfd_aarch64_elf_resolve_relocation): Add
	BFD_RELOC_MORELLO_CAPINIT and BFD_RELOC_MORELLO_RELATIVE.
	* libbfd.h (bfd_reloc_code_real_names): Likewise.
	* reloc.c: Likewise.
	* bfd-in2.h: Regenerate.

gas/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* config/tc-aarch64.c (s_aarch64_capinit): New function.
	(md_pseudo_table): Use it.
	(md_apply_fix): Add BFD_RELOC_MORELLO_CAPINIT.
	(aarch64_fix_adjustable): Return FALSE for capabilities.
	* testsuite/gas/aarch64/morello-capinit.d: New test file.
	* testsuite/gas/aarch64/morello-capinit.s: Likewise.

include/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* elf/aarch64.h (R_MORELLO_CAPINIT, R_MORELLO_RELATIVE): New
	relocations.

ld/ChangeLog:

2020-10-20  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>

	* testsuite/ld-aarch64/aarch64-elf.exp: Add test.
	* testsuite/ld-aarch64/morello-capinit.d: New file.
	* testsuite/ld-aarch64/morello-capinit.ld: New file.
	* testsuite/ld-aarch64/morello-capinit.s: New file.