Pull compiler version requirement update from Arnd Bergmann:
 "Require gcc-8 and binutils-2.30

  x86 already uses gcc-8 as the minimum version, this changes all other
  architectures to the same version. gcc-8 is used is Debian 10 and Red
  Hat Enterprise Linux 8, both of which are still supported, and
  binutils 2.30 is the oldest corresponding version on those.

  Ubuntu Pro 18.04 and SUSE Linux Enterprise Server 15 both use gcc-7 as
  the system compiler but additionally include toolchains that remain
  supported.

  With the new minimum toolchain versions, a number of workarounds for
  older versions can be dropped, in particular on x86_64 and arm64.
  Importantly, the updated compiler version allows removing two of the
  five remaining gcc plugins, as support for sancov and structeak
  features is already included in modern compiler versions.

  I tried collecting the known changes that are possible based on the
  new toolchain version, but expect that more cleanups will be possible.

  Since this touches multiple architectures, I merged the patches
  through the asm-generic tree."

* tag 'gcc-minimum-version-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic:
  Makefile.kcov: apply needed compiler option unconditionally in CFLAGS_KCOV
  Documentation: update binutils-2.30 version reference
  gcc-plugins: remove SANCOV gcc plugin
  Kbuild: remove structleak gcc plugin
  arm64: drop binutils version checks
  raid6: skip avx512 checks
  kbuild: require gcc-8 and binutils-2.30

This is the follow-up to commit a79be02bba5c ("Fix mis-uses of
'cc-option' for warning disablement") where I mentioned that the best
fix would be to just make 'cc-option' a bit smarter, and work for all
compiler options, including the '-Wno-xyzzy' pattern that it used to
accept unknown options for.

It turns out that fixing cc-option is pretty straightforward: just
rewrite any '-Wno-xyzzy' option pattern to use '-Wxyzzy' instead for
testing.

That makes the whole artificial distinction between 'cc-option' and
'cc-disable-warning' go away, and we can happily forget about the odd
build rule that you have to treat compiler options that disable warnings
specially.

The 'cc-disable-warning' helper remains as a backwards compatibility
syntax for now, but is implemented in terms of the new and improved
cc-option.

Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Commit a3e8fe814ad1 ("x86/build: Raise the minimum GCC version to 8.1")
raised the minimum compiler version as enforced by Kbuild to gcc-8.1
and clang-15 for x86.

This is actually the same gcc version that has been discussed as the
minimum for all architectures several times in the past, with little
objection. A previous concern was the kernel for SLE15-SP7 needing to
be built with gcc-7. As this ended up still using linux-6.4 and there
is no plan for an SP8, this is no longer a problem.

Change it for all architectures and adjust the documentation accordingly.
A few version checks can be removed in the process.  The binutils
version 2.30 is the lowest version used in combination with gcc-8 on
common distros, so use that as the corresponding minimum.

Link: https://lore.kernel.org/lkml/20240925150059.3955569-32-ardb+git@google.com/
Link: https://lore.kernel.org/lkml/871q7yxrgv.wl-tiwai@suse.de/
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

GNU Make 4.3 changed the behavior of `#` inside commands in commit
c6966b323811 ("[SV 20513] Un-escaped # are not comments in function
invocations"):

    * WARNING: Backward-incompatibility!
      Number signs (#) appearing inside a macro reference or function invocation
      no longer introduce comments and should not be escaped with backslashes:
      thus a call such as:
        foo := $(shell echo '#')
      is legal.  Previously the number sign needed to be escaped, for example:
        foo := $(shell echo '\#')
      Now this latter will resolve to "\#".  If you want to write makefiles
      portable to both versions, assign the number sign to a variable:
        H := \#
        foo := $(shell echo '$H')
      This was claimed to be fixed in 3.81, but wasn't, for some reason.
      To detect this change search for 'nocomment' in the .FEATURES variable.

Unlike other commits in the kernel about this issue, such as commit
633174a7046e ("lib/raid6/test/Makefile: Use $(pound) instead of \#
for Make 4.3"), that fixed the issue for newer GNU Makes, in our case
it was the opposite, i.e. we need to fix it for the older ones: someone
building with e.g. 4.2.1 gets the following error:

    scripts/Makefile.compiler:81: *** unterminated call to function 'call': missing ')'.  Stop.

Thus use the existing variable to fix it.

Reported-by: moyi geek <1441339168@qq.com>
Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/291565/topic/x/near/512001985
Cc: stable@vger.kernel.org
Fixes: e72a076c620f ("kbuild: fix issues with rustc-option")
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250414171241.2126137-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

If KASAN is enabled, and one runs in a clean repository e.g.:

    make LLVM=1 prepare
    make LLVM=1 prepare

Then the Rust code gets rebuilt, which should not happen.

The reason is some of the LLVM KASAN `rustc` flags are added in the
second run:

    -Cllvm-args=-asan-instrumentation-with-call-threshold=10000
    -Cllvm-args=-asan-stack=0
    -Cllvm-args=-asan-globals=1
    -Cllvm-args=-asan-kernel-mem-intrinsic-prefix=1

Further runs do not rebuild Rust because the flags do not change anymore.

Rebuilding like that in the second run is bad, even if this just happens
with KASAN enabled, but missing flags in the first one is even worse.

The root issue is that we pass, for some architectures and for the moment,
a generated `target.json` file. That file is not ready by the time `rustc`
gets called for the flag test, and thus the flag test fails just because
the file is not available, e.g.:

    $ ... --target=./scripts/target.json ... -Cllvm-args=...
    error: target file "./scripts/target.json" does not exist

There are a few approaches we could take here to solve this. For instance,
we could ensure that every time that the config is rebuilt, we regenerate
the file and recompute the flags. Or we could use the LLVM version to
check for these flags, instead of testing the flag (which may have other
advantages, such as allowing us to detect renames on the LLVM side).

However, it may be easier than that: `rustc` is aware of the `-Cllvm-args`
regardless of the `--target` (e.g. I checked that the list printed
is the same, plus that I can check for these flags even if I pass
a completely unrelated target), and thus we can just eliminate the
dependency completely.

Thus filter out the target.

This does mean that `rustc-option` cannot be used to test a flag that
requires the right target, but we don't have other users yet, it is a
minimal change and we want to get rid of custom targets in the future.

We could only filter in the case `target.json` is used, to make it work
in more cases, but then it would be harder to notice that it may not
work in a couple architectures.

Cc: Matthew Maurer <mmaurer@google.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: stable@vger.kernel.org
Fixes: e3117404b411 ("kbuild: rust: Enable KASAN support")
Tested-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250408220311.1033475-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Introduce `rustc-min-version` support function that mimics
`{gcc,clang}-min-version` ones, following commit 88b61e3bff93
("Makefile.compiler: replace cc-ifversion with compiler-specific macros").

In addition, use it in the first use case we have in the kernel (which
was done independently to minimize the changes needed for the fix).

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Fiona Behrens <me@Kloenk.dev>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Currently, Kbuild always operates in the output directory of the kernel,
even when building external modules. This increases the risk of external
module Makefiles attempting to write to the kernel directory.

This commit switches the working directory to the external module
directory, allowing the removal of the $(KBUILD_EXTMOD)/ prefix from
some build artifacts.

The command for building external modules maintains backward
compatibility, but Makefiles that rely on working in the kernel
directory may break. In such cases, $(objtree) and $(srctree) should
be used to refer to the output and source directories of the kernel.

The appearance of the build log will change as follows:

[Before]

  $ make -C /path/to/my/linux M=/path/to/my/externel/module
  make: Entering directory '/path/to/my/linux'
    CC [M]  /path/to/my/externel/module/helloworld.o
    MODPOST /path/to/my/externel/module/Module.symvers
    CC [M]  /path/to/my/externel/module/helloworld.mod.o
    CC [M]  /path/to/my/externel/module/.module-common.o
    LD [M]  /path/to/my/externel/module/helloworld.ko
  make: Leaving directory '/path/to/my/linux'

[After]

  $ make -C /path/to/my/linux M=/path/to/my/externel/module
  make: Entering directory '/path/to/my/linux'
  make[1]: Entering directory '/path/to/my/externel/module'
    CC [M]  helloworld.o
    MODPOST Module.symvers
    CC [M]  helloworld.mod.o
    CC [M]  .module-common.o
    LD [M]  helloworld.ko
  make[1]: Leaving directory '/path/to/my/externel/module'
  make: Leaving directory '/path/to/my/linux'

Printing "Entering directory" twice is cumbersome. This will be
addressed later.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>

Fix a few different compiler errors that cause rustc-option to give
wrong results.

If KBUILD_RUSTFLAGS or the flags being tested contain any -Z flags, then
the error below is generated. The RUSTC_BOOTSTRAP environment variable
is added to fix this error.

	error: the option `Z` is only accepted on the nightly compiler
	help: consider switching to a nightly toolchain: `rustup default nightly`
	note: selecting a toolchain with `+toolchain` arguments require a rustup proxy;
	      see <https://rust-lang.github.io/rustup/concepts/index.html>
	note: for more information about Rust's stability policy, see
	      <https://doc.rust-lang.org/book/appendix-07-nightly-rust.html#unstable-features>
	error: 1 nightly option were parsed

Note that RUSTC_BOOTSTRAP is also defined in the top-level Makefile,
but Make-exported variables are unfortunately *not* inherited. That said,
this is changing as of commit 98da874c4303 ("[SV 10593] Export variables
to $(shell ...) commands"), which is part of Make 4.4.

The probe may also fail with the error message below. To fix it,
the /dev/null argument is replaced with a file containing the crate
attribute #![no_core]. The #![no_core] attribute ensures that rustc does
not look for the standard library. It's not possible to instead supply
a standard library (i.e. `core`) to rustc, as we need `rustc-option`
before the Rust standard library is compiled.

	error[E0463]: can't find crate for `std`
	  |
	  = note: the `aarch64-unknown-none` target may not be installed
	  = help: consider downloading the target with `rustup target add aarch64-unknown-none`
	  = help: consider building the standard library from source with `cargo build -Zbuild-std`

The -o and --out-dir parameters are altered to fix this warning:

	warning: ignoring --out-dir flag due to -o flag

The --sysroot flag is provided as we would otherwise require it to be
present in KBUILD_RUSTFLAGS. The --emit=obj flag is used to write the
resulting object file to /dev/null instead of writing it to a file
in $(TMPOUT).

I verified that the Kconfig version of rustc-option doesn't have the
same issues.

Fixes: c42297438aee ("kbuild: rust: Define probing macros for rustc")
Co-developed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20241009-rustc-option-bootstrap-v3-1-5fa0d520efba@google.com
[ Reworded as discussed in the list. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

cc-option-yn and cc-disable-warning duplicate the compile command seen
a few lines above. These can be defined based on cc-option.

I also refactored rustc-option-yn in the same way, although there are
currently no users of it.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20241009102821.2675718-1-masahiroy@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Creates flag probe macro variants for `rustc`. These are helpful
because:

1. The kernel now supports a minimum `rustc` version rather than a
   single version.
2. `rustc` links against a range of LLVM revisions, occasionally even
   ones without an official release number. Since the availability of
   some Rust flags depends on which LLVM it has been linked against,
   probing is necessary.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Link: https://github.com/Rust-for-Linux/linux/pull/1087
Link: https://lore.kernel.org/r/20240820194910.187826-2-mmaurer@google.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>