[v5,04/14] tables.h: add linker table support

A linker table is a data structure that is stitched together from items
in multiple object files. Linux has historically implicitly used linker
tables for ages, however they were all built in an adhoc manner which
requires linker script modifications, per architecture. This adds a
general linker table solution so that a new linker table can be
implemented by changing C code only. The Linux linker table was
inspired by Michael Brown's iPXE's linker table solution, it has been
been completely re-written and adapted for integration and use on Linux.

The same philosophy is borrowed, extended and further simplified:

Linker tables enable an extremely light weight linker build time
solution for feature ordering and selection, this can help to both
simplify init sequences in a generic fashion and helps avoiding code
bit-rotting when desirable. Further changes will be added later
which will make more evident how code bit rot can be avoided using
linker tables.

v5:
o Use ..tbl.* instead of .tbl.* as suggested by Nicholas Piggin.
  This is the typical way to avoid clashes with compiler generated
  sections.
o Replace section macros with section names
o Dropped SECTION_RNG_ALL()
o Fix documentation typos
o To make this easier to read, as per Nicholas Piggin, add our own
  LINKTABLE_START(), LINKTABLE_END(). After reviewing the changes
  affected by this it seemed clearer and better then to also
  use our own specific LINKTABLE_SIZE(), LINKTABLE_EMPTY() and
  LINKTABLE_ALIGNMENT() as well.
o Clarifies SECTION_TBL_RO needs to be kept since some toolchains
  are buggy, and so we also add SECTION_TBL_RO_STR.
o We were using LINUX_SECTION_START() and LINUX_SECTION_END() in some places
  but in some other places VMLINUX_SYMBOL(name), VMLINUX_SYMBOL(name##__end).
  Since we are adding LINKTABLE_START() and LINKTABLE_END() just use those
  consistently.
o Fix DEFINE_LINKTABLE_INIT() by making it use DECLARE_LINKTABLE_RO()
  which forces const.
o Fix powerpc .text use: it does not use TEXT_TEXT so we must
  add our *(SORT(.text.tbl.*)) to its linker script manually.

v4:

o Split out kbuild additions to help with code bit rot into
  its own patch
o tons of documentation love
o fix arch/x86/tools/relocs.c typo - which caused compilation issues
  on old toolchains
o add c6x toolchain work around as discussed with Mark Salter
o sprinkle a few more needed VMLINUX_SYMBOL() - fixes
  compilation on blackfin
o suggested name changes by boris:
- %s/SECTION_TYPE_RANGES/rng/g
- %s/SECTION_TYPE/SECTION_CORE/g
- %s/section_type_asmtype/section_core_type/g
- %s/section_type/section_core/g
- %s/section_rng/set_section_rng/g
- Drop DECLARE_SECTION_TBL() -- this is an asm equivalent
  DEFINE_LINKTABLE() -- this however is not used yet, and it requires
  a bit more work to match the C code definitions.
o drop tools/include/linux/sections.h in favor of the more popular open
  coding the names for tools
o expand documentation to include module support
o add maintaners
o Use generic-y
o move .text.tbl before unlikely to match the other sections

v3:

o addressed initial modular support test cases
o added generic asm macros so linker tables can be used in
  asm code / C asm calls
o section ranges are now split up into their own set of files
o use asm/sections.h instead of linux/sections.h for the linker
  script
o add a sections.h file for each architecture that was missing one,
  this is needed now as we'll be relying on sections.h for custom
  section types in code rather than custom architecture specific
  linker script hacks.
o full rewrite at this point, decided to pick copyleft-next license
  for this work

v2:

o modified completely to match feedback by community, made equivalent
  modifications to userspace solution. This is pretty much a complete
  rewrite of how we present and use linker tables. By using standard
  sections we no longer have to make custom linker script extensions
  for each new linker table solution, you just pick a linker table
  type by section type.
o extend documention considerably, including use of kdoc
o drop ICC hacks per popular request to ignore such issues for now
o use sections.h - this lets us streamline a clean use case of
  well documented sections. To help further with this make use of
  SECTION_TBL() to allow use of these in code and SECTION_TBL_ALL()
  on linker scripts, as well as SECTION_TBL_ALL_STR() on relocs.c
  when needed.

Cc: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
---
 Documentation/sections/index.rst         |   1 +
 Documentation/sections/linker-tables.rst | 212 +++++++++++
 MAINTAINERS                              |  10 +
 arch/alpha/include/asm/Kbuild            |   1 +
 arch/arc/include/asm/Kbuild              |   1 +
 arch/arm/include/asm/Kbuild              |   1 +
 arch/arm64/include/asm/Kbuild            |   1 +
 arch/avr32/include/asm/Kbuild            |   1 +
 arch/blackfin/include/asm/Kbuild         |   1 +
 arch/c6x/include/asm/tables.h            |  26 ++
 arch/cris/include/asm/Kbuild             |   1 +
 arch/frv/include/asm/Kbuild              |   1 +
 arch/h8300/include/asm/Kbuild            |   1 +
 arch/hexagon/include/asm/Kbuild          |   1 +
 arch/ia64/include/asm/Kbuild             |   1 +
 arch/m32r/include/asm/Kbuild             |   1 +
 arch/m68k/include/asm/Kbuild             |   1 +
 arch/metag/include/asm/Kbuild            |   1 +
 arch/microblaze/include/asm/Kbuild       |   1 +
 arch/mips/include/asm/Kbuild             |   1 +
 arch/mn10300/include/asm/Kbuild          |   1 +
 arch/nios2/include/asm/Kbuild            |   1 +
 arch/openrisc/include/asm/Kbuild         |   1 +
 arch/parisc/include/asm/Kbuild           |   1 +
 arch/powerpc/include/asm/Kbuild          |   1 +
 arch/powerpc/kernel/vmlinux.lds.S        |   1 +
 arch/s390/include/asm/Kbuild             |   1 +
 arch/score/include/asm/Kbuild            |   1 +
 arch/sh/include/asm/Kbuild               |   1 +
 arch/sparc/include/asm/Kbuild            |   1 +
 arch/tile/include/asm/Kbuild             |   1 +
 arch/um/include/asm/Kbuild               |   1 +
 arch/unicore32/include/asm/Kbuild        |   1 +
 arch/x86/include/asm/Kbuild              |   1 +
 arch/x86/tools/relocs.c                  |   2 +
 arch/xtensa/include/asm/Kbuild           |   1 +
 include/asm-generic/tables.h             |  48 +++
 include/asm-generic/vmlinux.lds.h        |   6 +
 include/linux/tables.h                   | 612 +++++++++++++++++++++++++++++++
 39 files changed, 948 insertions(+)
 create mode 100644 Documentation/sections/linker-tables.rst
 create mode 100644 arch/c6x/include/asm/tables.h
 create mode 100644 include/asm-generic/tables.h
 create mode 100644 include/linux/tables.h

[v5,04/14] tables.h: add linker table support

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