Several architectures provide an API to enable the FPU and run
floating-point SIMD code in kernel space.  However, the function names,
header locations, and semantics are inconsistent across architectures, and
FPU support may be gated behind other Kconfig options.

provide a standard way for architectures to declare that kernel space
FPU support is available. Architectures selecting this option must
implement what is currently the most common API (kernel_fpu_begin() and
kernel_fpu_end(), plus a new function kernel_fpu_available()) and
provide the appropriate CFLAGS for compiling floating-point C code.

Link: https://lkml.kernel.org/r/20240329072441.591471-2-samuel.holland@sifive.com


Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: WANG Xuerui <git@xen0n.name>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Currently, Kbuild produces inconsistent results in some cases.

You can do an interesting experiment using the --shuffle option, which
is supported by GNU Make 4.4 or later.

Set CONFIG_KVM_INTEL=y and CONFIG_KVM_AMD=m (or vice versa), and repeat
incremental builds w/wo --shuffle=reverse.

  $ make
    [ snip ]
    CC      arch/x86/kvm/kvm-asm-offsets.s

  $ make --shuffle=reverse
    [ snip ]
    CC [M]  arch/x86/kvm/kvm-asm-offsets.s

  $ make
    [ snip ]
    CC      arch/x86/kvm/kvm-asm-offsets.s

arch/x86/kvm/kvm-asm-offsets.s is rebuilt every time w/wo the [M] marker.

arch/x86/kvm/kvm-asm-offsets.s is built as built-in when it is built as
a prerequisite of arch/x86/kvm/kvm-intel.o, which is built-in.

arch/x86/kvm/kvm-asm-offsets.s is built as modular when it is built as
a prerequisite of arch/x86/kvm/kvm-amd.o, which is a module.

Another odd example is single target builds.

When CONFIG_LKDTM=m, drivers/misc/lkdtm/rodata.o can be built as
built-in or modular, depending on how it is built.

  $ make drivers/misc/lkdtm/lkdtm.o
    [ snip ]
    CC [M]  drivers/misc/lkdtm/rodata.o

  $ make drivers/misc/lkdtm/rodata.o
    [ snip ]
    CC      drivers/misc/lkdtm/rodata.o

drivers/misc/lkdtm/rodata.o is built as modular when it is built as a
prerequisite of another, but built as built-in when it is a final
target.

The same thing happens to drivers/memory/emif-asm-offsets.s when
CONFIG_TI_EMIF_SRAM=m.

  $ make drivers/memory/ti-emif-sram.o
    [ snip ]
    CC [M]  drivers/memory/emif-asm-offsets.s

  $ make drivers/memory/emif-asm-offsets.s
    [ snip ]
    CC      drivers/memory/emif-asm-offsets.s

This is because the part-of-module=y flag defined for the modules is
inherited by its prerequisites.

Target-specific variables are likely intended only for local use.
This commit adds 'private' to them.

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

The $(wildcard ) is called in quiet_cmd_rmfiles.

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

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

    src := $(obj)

When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.

This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.

To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.

Going forward, the variables used ...

There is an issue in clang's ThinLTO caching (enabled for the kernel via
'--thinlto-cache-dir') with .incbin, which the kernel occasionally uses
to include data within the kernel, such as the .config file for
/proc/config.gz. For example, when changing the .config and rebuilding
vmlinux, the copy of .config in vmlinux does not match the copy of
.config in the build folder:

  $ echo 'CONFIG_LTO_NONE=n
  CONFIG_LTO_CLANG_THIN=y
  CONFIG_IKCONFIG=y
  CONFIG_HEADERS_INSTALL=y' >kernel/configs/repro.config

  $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 clean defconfig repro.config vmlinux
  ...

  $ grep CONFIG_HEADERS_INSTALL .config
  CONFIG_HEADERS_INSTALL=y

  $ scripts/extract-ikconfig vmlinux | grep CONFIG_HEADERS_INSTALL
  CONFIG_HEADERS_INSTALL=y

  $ scripts/config -d HEADERS_INSTALL

  $ make -kj"$(nproc)" ARCH=x86_64 LLVM=1 vmlinux
  ...
    UPD     kernel/config_data
    GZIP    kernel/config_data.gz
    CC      kernel/configs.o
  ...
    LD      vmlinux
  ...

  $ grep CONFIG_HEADERS_INSTALL .config
  # CONFIG_HEADERS_INSTALL is not set

  $ scripts/extract-ikconfig vmlinux | grep CONFIG_HEADERS_INSTALL
  CONFIG_HEADERS_INSTALL=y

Without '--thinlto-cache-dir' or when using full LTO, this issue does
not occur.

Benchmarking incremental builds on a few different machines with and
without the cache shows a 20% increase in incremental build time without
the cache when measured by touching init/main.c and running 'make all'.

ARCH=arm64 defconfig + CONFIG_LTO_CLANG_THIN=y on an arm64 host:

  Benchmark 1: With ThinLTO cache
    Time (mean ± σ):     56.347 s ±  0.163 s    [User: 83.768 s, System: 24.661 s]
    Range (min … max):   56.109 s … 56.594 s    10 runs

  Benchmark 2: Without ThinLTO cache
    Time (mean ± σ):     67.740 s ±  0.479 s    [User: 718.458 s, System: 31.797 s]
    Range (min … max):   67.059 s … 68.556 s    10 runs

  Summary
    With ThinLTO cache ran
      1.20 ± 0.01 times faster than Without ThinLTO cache

ARCH=x86_64 defconfig + CONFIG_LTO_CLANG_THIN=y on an x86_64 host:

  Benchmark 1: With ThinLTO cache
    Time (mean ± σ):     85.772 s ±  0.252 s    [User: 91.505 s, System: 8.408 s]
    Range (min … max):   85.447 s … 86.244 s    10 runs

  Benchmark 2: Without ThinLTO cache
    Time (mean ± σ):     103.833 s ±  0.288 s    [User: 232.058 s, System: 8.569 s]
    Range (min … max):   103.286 s … 104.124 s    10 runs

  Summary
    With ThinLTO cache ran
      1.21 ± 0.00 times faster than Without ThinLTO cache

While it is unfortunate to take this performance improvement off the
table, correctness is more important. If/when this is fixed in LLVM, it
can potentially be brought back in a conditional manner. Alternatively,
a developer can just disable LTO if doing incremental compiles quickly
is important, as a full compile cycle can still take over a minute even
with the cache and it is unlikely that LTO will result in functional
differences for a kernel change.

Cc: stable@vger.kernel.org
Fixes: dc5723b0

 ("kbuild: add support for Clang LTO")
Reported-by: Yifan Hong <elsk@google.com>
Closes: https://github.com/ClangBuiltLinux/linux/issues/2021


Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
Closes: https://lore.kernel.org/r/20220327115526.cc4b0ff55fc53c97683c3e4d@kernel.org/


Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Running dtbs_check and dt_compatible_check targets really only depend
on processed-schema.json, but the dependency is 'dt_binding_check'. That
was sort worked around with the CHECK_DT_BINDING variable in order to
skip some of the work that 'dt_binding_check' does. It still runs the
full checks of the schemas which is not necessary and adds 10s of
seconds to the build time. That's significant when checking only a few
DTBs and with recent changes that have improved the validation time by
6-7x.

Add a new target, dt_binding_schema, which just builds
processed-schema.json and can be used as the dependency for other
targets. The scripts_dtc dependency isn't needed either as the examples
aren't built for it.

Signed-off-by: Rob Herring <robh@kernel.org>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Commit 25b146c5 ("kbuild: allow Kbuild to start from any directory")
exported abs_srctree and abs_objtree to avoid recomputation after the
sub-make. However, this approach turned out to be fragile.

Commit 5fa94ceb

 ("kbuild: set correct abs_srctree and abs_objtree
for package builds") moved them above "ifneq ($(sub_make_done),1)",
eliminating the need for exporting them.

These are only needed in the top Makefile. If an absolute path is
required in sub-directories, you can use $(abspath ) or $(realpath )
as needed.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Commit 3b9ab248

 ("kbuild: use 4-space indentation when followed
by conditionals") introduced inconsistent indentation because it
deliberately touched only the conditional directives to minimize the
change set.

This commit reformats some blocks in the top Makefile so they are
consistently indented with 4 spaces.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>

`rustc` (like Cargo) may take advantage of the jobserver at any time
(e.g. for backend parallelism, or eventually frontend too). In the kernel,
we call `rustc` with `-Ccodegen-units=1` (and `-Zthreads` is 1 so far),
so we do not expect parallelism. However, in the upcoming Rust 1.76.0, a
warning is emitted by `rustc` [1] when it cannot connect to the jobserver
it was passed (in many cases, but not all: compiling and `--print sysroot`
do, but `--version` does not). And given GNU Make always passes
the jobserver in the environment variable (even when a line is deemed
non-recursive), `rustc` will end up complaining about it (in particular
in Make 4.3 where there is only the simple pipe jobserver style).

One solution is to remove the jobserver from `MAKEFLAGS`. However, we
can mark the lines with calls to `rustc` (and Cargo) as recursive, which
looks simpler. This is being documented as a recommendation in `rustc`
[2] and allows us to be ready for the time we may use parallelism inside
`rustc` (potentially now, if a user passes `-Zthreads`). Thus do so.

Similarly, do the same for `rustdoc` and `cargo` calls.

Finally, there is one case that the solution does not cover, which is the
`$(shell ...)` call we have. Thus, for that one, set an empty `MAKEFLAGS`
environment variable.

Link: https://github.com/rust-lang/rust/issues/120515

 [1]
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://github.com/rust-lang/rust/pull/121564 [2]
Link: https://lore.kernel.org/r/20240217002638.57373-1-ojeda@kernel.org


[ Reworded to add link to PR documenting the recommendation. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

GCC recently added option -fmin-function-alignment, which should appear
in GCC 14. Unlike -falign-functions, this option causes all functions to
be aligned at the specified value, including the cold ones.

In particular, when an arm64 kernel is built with
DYNAMIC_FTRACE_WITH_CALL_OPS=y, the 8-byte function alignment is
required for correct functionality. This was done by -falign-functions=8
and having workarounds in the kernel to force the compiler to follow
this alignment. The new -fmin-function-alignment option directly
guarantees it.

Detect availability of -fmin-function-alignment and use it instead of
-falign-functions when present. Introduce CC_HAS_SANE_FUNCTION_ALIGNMENT
and enable __cold to work as expected when it is set.

Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Now that the minimum supported version of LLVM for building the kernel has
been bumped to 13.0.1, the inner ifeq statement is always false, as the
build will fail during the configuration stage for older LLVM versions.

This effectively reverts commit 24845dcb ("Makefile: LTO: have linker
check -Wframe-larger-than") and its follow up fix, commit 0236526d
("Makefile: lto: Pass -warn-stack-size only on LLD < 13.0.0").

Link: https://lkml.kernel.org/r/20240125-bump-min-llvm-ver-to-13-0-1-v1-2-f5ff9bda41c5@kernel.org


Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: "Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Conor Dooley <conor@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Retrieve the list of *.dtb(o) files from arch/*/boot/dts/dtbs-list
instead of traversing the directory tree again.

Please note that 'make dtbs_install' installs *.dtb(o) files directly
added to dtb-y because scripts/Makefile.dtbinst installs $(dtb-y)
without expanding the -dtbs suffix.

This commit preserves this behavior.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

It is useful to have a list of all *.dtb and *.dtbo files generated
from the current build.

With this commit, 'make dtbs' creates arch/*/boot/dts/dtbs-list, which
lists the dtb(o) files created in the current build. It maintains the
order of the dtb-y additions in Makefiles although the order is not
important for DTBs. It is a (good) side effect through the reuse of the
modules.order rule.

Please note this list only includes the files directly added to dtb-y.

For example, consider this case:

    foo-dtbs := foo_base.dtb foo_overlay.dtbo
    dtb-y := foo.dtb

In this example, the list will include foo.dtb, but not foo_base.dtb
or foo_overlay.dtbo.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

GNU Make manual [1] clearly forbids a tab at the beginning of the
conditional directive line:
 "Extra spaces are allowed and ignored at the beginning of the
  conditional directive line, but a tab is not allowed."

This will not work for the next release of GNU Make, hence commit
82175d1f ("kbuild: Replace tabs with spaces when followed by
conditionals") replaced the inappropriate tabs with 8 spaces.

However, the 8-space indentation cannot be visually distinguished.
Linus suggested 2-4 spaces for those nested if-statements. [2]

This commit redoes the replacement with 4 spaces.

[1]: https://www.gnu.org/software/make/manual/make.html#Conditional-Syntax
[2]: https://lore.kernel.org/all/CAHk-=whJKZNZWsa-VNDKafS_VfY4a5dAjG-r8BZgWk_a-xSepw@mail.gmail.com/



Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Eventually we want all architectures to be using the target as defined
by rustc. However currently some architectures can't do that and are
using the target.json specification. This puts in place the foundation
to allow the use of the builtin target definition or a target.json
specification.

Signed-off-by: Jamie Cunliffe <Jamie.Cunliffe@arm.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20231020155056.3495121-2-Jamie.Cunliffe@arm.com


[catalin.marinas@arm.com: squashed loongarch ifneq fix from WANG Rui]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

This is needed for the future (post make-4.4.1) versions of gnu make.

Starting from https://git.savannah.gnu.org/cgit/make.git/commit/?id=07fcee35f058a876447c8a021f9eb1943f902534
gnu make won't allow conditionals to follow recipe prefix.

For example there is a tab followed by ifeq on line 324 in the root Makefile.
With the new make this conditional causes the following

$ make cpu.o
/home/dgoncharov/src/linux-kbuild/Makefile:2063: *** missing 'endif'.  Stop.
make: *** [Makefile:240: __sub-make] Error 2

This patch replaces tabs followed by conditionals with 8 spaces.

See https://savannah.gnu.org/bugs/?64185 and
https://savannah.gnu.org/bugs/?64259

 for details.

Signed-off-by: Dmitry Goncharov <dgoncharov@users.sf.net>
Reported-by: Martin Dorey <martin.dorey@hitachivantara.com>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

W=c and W=e are supported.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

-Wstringop-overflow is buggy in GCC-11. Therefore, we should disable
this option specifically for that compiler version. To achieve this,
we introduce a new configuration option: GCC11_NO_STRINGOP_OVERFLOW.

The compiler option related to string operation overflow is now managed
under configuration CC_STRINGOP_OVERFLOW. This option is enabled by
default for all other versions of GCC that support it.

Link: https://lore.kernel.org/lkml/b3c99290-40bc-426f-b3d2-1aa903f95c4e@embeddedor.com/
Link: https://lore.kernel.org/lkml/20231128091351.2bfb38dd@canb.auug.org.au/


Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/linux-hardening/ZWj1+jkweEDWbmAR@work/


Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

It seems that we have finished addressing all the remaining
issues regarding -Wstringop-overflow. So, we are now in good
shape to enable this compiler option globally.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>