Pull Kbuild fixes from Masahiro Yamada:

 - add compile_commands.json to .gitignore

 - fix false-positive warning from gen_compile_commands.py after
   allnoconfig build

 - remove unused code

* tag 'kbuild-fixes-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
  kbuild: remove unused single-used-m
  gen_compile_commands: lower the entry count threshold
  .gitignore: Add compilation database file
  kbuild: remove unused objectify macro

This is unused since commit 9f69a496f100 ("kbuild: split out *.mod out
of {single,multi}-used-m rules").

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Running gen_compile_commands.py after building the kernel with
allnoconfig gave this:

$ ./scripts/gen_compile_commands.py
WARNING: Found 449 entries. Have you compiled the kernel?

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Commit 415008af3219 ("docs-rst: convert lsm from DocBook to ReST")
removed the last users of this macro.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Bring in a set of post-thrashup fixes from Mauro.

Pull more Kbuild updates from Masahiro Yamada:

 - match the directory structure of the linux-libc-dev package to that
   of Debian-based distributions

 - fix incorrect include/config/auto.conf generation when Kconfig
   creates it along with the .config file

 - remove misleading $(AS) from documents

 - clean up precious tag files by distclean instead of mrproper

 - add a new coccinelle patch for devm_platform_ioremap_resource
   migration

 - refactor module-related scripts to read modules.order instead of
   $(MODVERDIR)/*.mod files to get the list of created modules

 - remove MODVERDIR

 - update list of header compile-test

 - add -fcf-protection=none flag to avoid conflict with the retpoline
   flags when CONFIG_RETPOLINE=y

 - misc cleanups

* tag 'kbuild-v5.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (25 commits)
  kbuild: add -fcf-protection=none when using retpoline flags
  kbuild: update compile-test header list for v5.3-rc1
  kbuild: split out *.mod out of {single,multi}-used-m rules
  kbuild: remove 'prepare1' target
  kbuild: remove the first line of *.mod files
  kbuild: create *.mod with full directory path and remove MODVERDIR
  kbuild: export_report: read modules.order instead of .tmp_versions/*.mod
  kbuild: modpost: read modules.order instead of $(MODVERDIR)/*.mod
  kbuild: modsign: read modules.order instead of $(MODVERDIR)/*.mod
  kbuild: modinst: read modules.order instead of $(MODVERDIR)/*.mod
  scsi: remove pointless $(MODVERDIR)/$(obj)/53c700.ver
  kbuild: remove duplication from modules.order in sub-directories
  kbuild: get rid of kernel/ prefix from in-tree modules.{order,builtin}
  kbuild: do not create empty modules.order in the prepare stage
  coccinelle: api: add devm_platform_ioremap_resource script
  kbuild: compile-test headers listed in header-test-m as well
  kbuild: remove unused hostcc-option
  kbuild: remove tag files by distclean instead of mrproper
  kbuild: add --hash-style= and --build-id unconditionally
  kbuild: get rid of misleading $(AS) from documents
  ...

Currently, *.mod is created as a side-effect of obj-m.

Split out *.mod as a dedicated build rule, which allows to unify
the %.c -> %.o rule, and remove the single-used-m rule.

This also makes the incremental build of allmodconfig faster because
it saves $(NM) invocation when there is no change in the module.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

The current format of *.mod is like this:

  line 1: directory path to the .ko file
  line 2: a list of objects linked into this module
  line 3: unresolved symbols (only when CONFIG_TRIM_UNUSED_KSYMS=y)

Now that *.mod and *.ko are created in the same directory, the line 1
provides no valuable information. It can be derived by replacing the
extension .mod with .ko. In fact, nobody uses the first line any more.

Cut down the first line.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

While descending directories, Kbuild produces objects for modules,
but do not link final *.ko files; it is done in the modpost.

To keep track of modules, Kbuild creates a *.mod file in $(MODVERDIR)
for every module it is building. Some post-processing steps read the
necessary information from *.mod files. This avoids descending into
directories again. This mechanism was introduced in 2003 or so.

Later, commit 551559e13af1 ("kbuild: implement modules.order") added
modules.order. So, we can simply read it out to know all the modules
with directory paths. This is easier than parsing the first line of
*.mod files.

$(MODVERDIR) has a flat directory structure, that is, *.mod files
are named only with base names. This is based on the assumption that
the module name is unique across the tree. This assumption is really
fragile.

Stephen Rothwell reported a race condition caused by a module name
conflict:

  https://lkml.org/lkml/2019/5/13/991

In parallel building, two different threads could write to the same
$(MODVERDIR)/*.mod simultaneously.

Non-unique module names are the source of all kind of troubles, hence
commit 3a48a91901c5 ("kbuild: check uniqueness of module names")
introduced a new checker script.

However, it is still fragile in the build system point of view because
this race happens before scripts/modules-check.sh is invoked. If it
happens again, the modpost will emit unclear error messages.

To fix this issue completely, create *.mod with full directory path
so that two threads never attempt to write to the same file.

$(MODVERDIR) is no longer needed.

Since modules with directory paths are listed in modules.order, Kbuild
is still able to find *.mod files without additional descending.

I also killed cmd_secanalysis; scripts/mod/sumversion.c computes MD4 hash
for modules with MODULE_VERSION(). When CONFIG_DEBUG_SECTION_MISMATCH=y,
it occurs not only in the modpost stage, but also during directory
descending, where sumversion.c may parse stale *.mod files. It would emit
'No such file or directory' warning when an object consisting a module is
renamed, or when a single-obj module is turned into a multi-obj module or
vice versa.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Nicolas Pitre <nico@fluxnic.net>

Towards the goal of removing MODVERDIR aka .tmp_versions, read out
modules.order to get the list of modules to be processed. This is
simpler than parsing *.mod files in .tmp_versions.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>