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Masahiro Yamada authored
Currently, linker options are tested by the coordination of $(CC) and
$(LD) because $(LD) needs some object to link.

As commit 86a9df59 ("kbuild: fix linker feature test macros when
cross compiling with Clang") addressed, we need to make sure $(CC)
and $(LD) agree the underlying architecture of the passed object.

This could be a bit complex when we combine tools from different groups.
For example, we can use clang for $(CC), but we still need to rely on
GCC toolchain for $(LD).

So, I was searching for a way of standalone testing of linker options.
A trick I found is to use '-v'; this not only prints the version string,
but also tests if the given option is recognized.

If a given option is supported,

  $ aarch64-linux-gnu-ld -v --fix-cortex-a53-843419
  GNU ld (Linaro_Binutils-2017.11) 2.28.2.20170706
  $ echo $?
  0

If unsupported,

  $ aarch64-linux-gnu-ld -v --fix-cortex-a53-843419
  GNU ld (crosstool-NG linaro-1.13.1-4.7-2013.04-20130415 - Linaro GCC 2013.04) 2.23.1
  aarch64-linux-gnu-ld: unrecognized option '--fix-cortex-a53-843419'
  aarch64-linux-gnu-ld: use the --help option for usage information
  $ echo $?
  1

Gold works likewise.

  $ aarch64-linux-gnu-ld.gold -v --fix-cortex-a53-843419
  GNU gold (Linaro_Binutils-2017.11 2.28.2.20170706) 1.14
  masahiro@pug:~/ref/linux$ echo $?
  0
  $ aarch64-linux-gnu-ld.gold -v --fix-cortex-a53-999999
  GNU gold (Linaro_Binutils-2017.11 2.28.2.20170706) 1.14
  aarch64-linux-gnu-ld.gold: --fix-cortex-a53-999999: unknown option
  aarch64-linux-gnu-ld.gold: use the --help option for usage information
  $ echo $?
  1

LLD too.

  $ ld.lld -v --gc-sections
  LLD 7.0.0 (http://llvm.org/git/lld.git 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
  $ echo $?
  0
  $ ld.lld -v --fix-cortex-a53-843419
  LLD 7.0.0 (http://llvm.org/git/lld.git 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
  $ echo $?
  0
  $ ld.lld -v --fix-cortex-a53-999999
  ld.lld: error: unknown argument: --fix-cortex-a53-999999
  LLD 7.0.0 (http://llvm.org/git/lld.git

 4a0e4190e74cea19f8a8dc625ccaebdf8b5d1585) (compatible with GNU linkers)
  $ echo $?
  1

Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
0294e6f4
Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.