This flag is specific to clang, where it is only used by the 32-bit and
64-bit ARM backends. In certain situations, the presence of this flag
will cause a warning, as shown by commit 6580c5c18fb3 ("um: clang: Strip
out -mno-global-merge from USER_CFLAGS").

Since commit 61163efae020 ("kbuild: LLVMLinux: Add Kbuild support for
building kernel with Clang") that added this flag back in 2014, there
have been quite a few changes to the GlobalMerge pass in LLVM. Building
several different ARCH=arm and ARCH=arm64 configurations with LLVM 11
(minimum) and 15 (current main version) with this flag removed (i.e.,
with the default of '-mglobal-merge') reveals no modpost warnings, so it
is likely that the issue noted in the comment is no longer relevant due
to changes in LLVM or modpost, meaning this flag can be removed.

If any new warnings show up that are a result of the removal of this
flag, it can be added back under arch/arm{,64}/Makefile to avoid
warnings on other architectures.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Pull Kbuild updates from Masahiro Yamada:

 - Add new environment variables, USERCFLAGS and USERLDFLAGS to allow
   additional flags to be passed to user-space programs.

 - Fix missing fflush() bugs in Kconfig and fixdep

 - Fix a minor bug in the comment format of the .config file

 - Make kallsyms ignore llvm's local labels, .L*

 - Fix UAPI compile-test for cross-compiling with Clang

 - Extend the LLVM= syntax to support LLVM=<suffix> form for using a
   particular version of LLVm, and LLVM=<prefix> form for using custom
   LLVM in a particular directory path.

 - Clean up Makefiles

* tag 'kbuild-v5.18-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
  kbuild: Make $(LLVM) more flexible
  kbuild: add --target to correctly cross-compile UAPI headers with Clang
  fixdep: use fflush() and ferror() to ensure successful write to files
  arch: syscalls: simplify uapi/kapi directory creation
  usr/include: replace extra-y with always-y
  certs: simplify empty certs creation in certs/Makefile
  certs: include certs/signing_key.x509 unconditionally
  kallsyms: ignore all local labels prefixed by '.L'
  kconfig: fix missing '# end of' for empty menu
  kconfig: add fflush() before ferror() check
  kbuild: replace $(if A,A,B) with $(or A,B)
  kbuild: Add environment variables for userprogs flags
  kbuild: unify cmd_copy and cmd_shipped

The LLVM make variable allows a developer to quickly switch between the
GNU and LLVM tools. However, it does not handle versioned binaries, such
as the ones shipped by Debian, as LLVM=1 just defines the tool variables
with the unversioned binaries.

There was some discussion during the review of the patch that introduces
LLVM=1 around versioned binaries, ultimately coming to the conclusion
that developers can just add the folder that contains the unversioned
binaries to their PATH, as Debian's versioned suffixed binaries are
really just symlinks to the unversioned binaries in /usr/lib/llvm-#/bin:

$ realpath /usr/bin/clang-14
/usr/lib/llvm-14/bin/clang

$ PATH=/usr/lib/llvm-14/bin:$PATH make ... LLVM=1

However, that can be cumbersome to developers who are constantly testing
series with different toolchains and versions. It is simple enough to
support these versioned binaries directly in the Kbuild system by
allowing the developer to specify the version suffix with LLVM=, which
is shorter than the above suggestion:

$ make ... LLVM=-14

It does not change the meaning of LLVM=1 (which will continue to use
unversioned binaries) and it does not add too much additional complexity
to the existing $(LLVM) code, while allowing developers to quickly test
their series with different versions of the whole LLVM suite of tools.

Some developers may build LLVM from source but not add the binaries to
their PATH, as they may not want to use that toolchain systemwide.
Support those developers by allowing them to supply the directory that
the LLVM tools are available in, as it is no more complex to support
than the version suffix change above.

$ make ... LLVM=/path/to/llvm/

Update and reorder the documentation to reflect these new additions.
At the same time, notate that LLVM=0 is not the same as just omitting it
altogether, which has confused people in the past.

Link: https://lore.kernel.org/r/20200317215515.226917-1-ndesaulniers@google.com/
Link: https://lore.kernel.org/r/20220224151322.072632223@infradead.org/
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Pull array-bounds updates from Kees Cook:
 "This enables -Warray-bounds and -Wzero-length-bounds, now that the
  many bug fixes have landed all over the place in the kernel, and in
  GCC itself[1].

  A couple fixes[2] for known corner-case issues currently live in my
  "pending-fixes" tree which I'm expecting to send next week if other
  maintainers still haven't picked them up.

  I'm also expecting we can enable -Wstringop-overflow next cycle, as
  there are only a few stragglers[3], but it might even be possible for
  this release"

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578
[2] https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=for-next/pending-fixes&id=2d253138910eec553fc706379914243d71de9b85
[3] https://github.com/KSPP/linux/issues/181

* tag 'array-bounds-v5.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  Makefile: Enable -Wzero-length-bounds
  Makefile: Enable -Warray-bounds

Pull Kbuild update for C11 language base from Masahiro Yamada:
 "Kbuild -std=gnu11 updates for v5.18

  Linus pointed out the benefits of C99 some years ago, especially
  variable declarations in loops [1]. At that time, we were not ready
  for the migration due to old compilers.

  Recently, Jakob Koschel reported a bug in list_for_each_entry(), which
  leaks the invalid pointer out of the loop [2]. In the discussion, we
  agreed that the time had come. Now that GCC 5.1 is the minimum
  compiler version, there is nothing to prevent us from going to
  -std=gnu99, or even straight to -std=gnu11.

  Discussions for a better list iterator implementation are ongoing, but
  this patch set must land first"

[1] https://lore.kernel.org/all/CAHk-=wgr12JkKmRd21qh-se-_Gs69kbPgR9x4C+Es-yJV2GLkA@mail.gmail.com/
[2] https://lore.kernel.org/lkml/86C4CE7D-6D93-456B-AA82-F8ADEACA40B7@gmail.com/

* tag 'kbuild-gnu11-v5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild:
  Kbuild: use -std=gnu11 for KBUILD_USERCFLAGS
  Kbuild: move to -std=gnu11
  Kbuild: use -Wdeclaration-after-statement
  Kbuild: add -Wno-shift-negative-value where -Wextra is used