CONFIG_IA64_ESI is a bool option. I do not know why the Makefile was
written like this, but this should not have any functional change.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

This reverts commit d79a2719.

According to the commit description, this ld-option test was added for
the gold linker at that time.

Commit 75959d44 ("kbuild: Fail if gold linker is detected") gave
up the gold linker support after all.

I tested the BFD linker from binutils 2.23 and LLD from LLVM 11.0.0.
Both of them support the -X option.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

When include/linux/export-internal.h is updated, .vmlinux.export.o
must be rebuilt, but it does not happen because its rule is hidden
behind scripts/link-vmlinux.sh.

Move it out of the shell script, so that Make can see the dependency
between vmlinux and .vmlinux.export.o.

Move the vmlinux rule to scripts/Makefile.vmlinux.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Do not build modules.builtin(.modinfo) as a side-effect of vmlinux.

There are no good reason to rebuild them just because any of vmlinux's
prerequistes (vmlinux.lds, .vmlinux.export.c, etc.) has been updated.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

With CONFIG_ZSTD_COMPRESS=m and CONFIG_ZSTD_DECOMPRESS=y we end up in
a situation when files from lib/zstd/common/ are compiled once to be
linked later for ZSTD_DECOMPRESS (build-in) and ZSTD_COMPRESS (module)
even though CFLAGS are different for builtins and modules.
So far somehow this was not a problem but enabling LLVM LTO exposes
the problem as:

ld.lld: error: linking module flags 'Code Model': IDs have conflicting values in 'lib/built-in.a(zstd_common.o at 5868)' and 'ld-temp.o'

This particular conflict is caused by KBUILD_CFLAGS=-mcmodel=medium vs.
KBUILD_CFLAGS_MODULE=-mcmodel=large , modules use the large model on
POWERPC as explained at
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/Makefile?h=v5.18-rc4#n127
but the current use of common files is wrong anyway.

This works around the issue by introducing a zstd_common module with
shared code.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Every EXPORT_SYMBOL creates __kstrtab_* and __kstrtabns_*, which
consumes 15-20% of the kallsyms entries.

For example, on the system built from the x86_64 defconfig,

  $ cat /proc/kallsyms | wc
     129527    388581   5685465
  $ cat /proc/kallsyms | grep __kstrtab | wc
      23489     70467   1187932

We already ignore __crc_* symbols populated by EXPORT_SYMBOL, so it
should be fine to ignore __kstrtab_* and __kstrtabns_* as well.

This makes vmlinux a bit smaller.

  $ size vmlinux.before vmlinux.after
     text    data     bss     dec     hex filename
  22785374        8559694 1413328 32758396        1f3da7c vmlinux.before
  22785374        8137806 1413328 32336508        1ed6a7c vmlinux.after
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

This gets rid of the pipe operator connected with 'cat'.

Also use getopt_long() to parse the command line.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Now that kallsyms.c parses the output from mksysmap, some symbols have
already been dropped.

Move comments to scripts/mksysmap. Also, make the grep command readable.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/mksysmap internally runs ${NM} (dropping some symbols).

When CONFIG_KALLSYMS=y, mksysmap creates .tmp_System.map, but it is
almost the same as the output from the ${NM} invocation in kallsyms().
It is true scripts/mksysmap drops some symbols, but scripts/kallsyms.c
ignores more anyway.

Keep the mksysmap output as *.syms, and reuse it for kallsyms and
'cmp -s'. It saves one ${NM} invocation.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Since commit 7b453719 ("kbuild: link symbol CRCs at final link,
removing CONFIG_MODULE_REL_CRCS"), __crc_* symbols never become
absolute.

Keep ignoring __crc_*, but update the comment.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Kbuild puts the objects listed in head-y at the head of vmlinux.
Conventionally, we do this for head*.S, which contains the kernel entry
point.

A counter approach is to control the section order by the linker script.
Actually, the code marked as __HEAD goes into the ".head.text" section,
which is placed before the normal ".text" section.

I do not know if both of them are needed. From the build system
perspective, head-y is not mandatory. If you can achieve the proper code
placement by the linker script only, it would be cleaner.

I collected the current head-y objects into head-object-list.txt. It is
a whitelist. My hope is it will be reduced in the long run.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

The objects placed at the head of vmlinux need special treatments:

 - arch/$(SRCARCH)/Makefile adds them to head-y in order to place
   them before other archives in the linker command line.

 - arch/$(SRCARCH)/kernel/Makefile adds them to extra-y instead of
   obj-y to avoid them going into built-in.a.

This commit gets rid of the latter.

Create vmlinux.a to collect all the objects that are unconditionally
linked to vmlinux. The objects listed in head-y are moved to the head
of vmlinux.a by using 'ar m'.

With this, arch/$(SRCARCH)/kernel/Makefile can consistently use obj-y
for builtin objects.

There is no *.o that is directly linked to vmlinux. Drop unneeded code
in scripts/clang-tools/gen_compile_commands.py.

$(AR) mPi needs 'T' to workaround the llvm-ar bug. The fix was suggested
by Nathan Chancellor [1].

[1]: https://lore.kernel.org/llvm/YyjjT5gQ2hGMH0ni@dev-arch.thelio-3990X/Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

V=1 (verbose build) shows commands executed by Make, but it may cause
misunderstanding.

For example, the following command shows the outstanding error message.

  $ make V=1 INSTALL_PATH=/tmp install
  test -e include/generated/autoconf.h -a -e include/config/auto.conf || (                \
  echo >&2;                                                       \
  echo >&2 "  ERROR: Kernel configuration is invalid.";           \
  echo >&2 "         include/generated/autoconf.h or include/config/auto.conf are missing.";\
  echo >&2 "         Run 'make oldconfig && make prepare' on kernel src to fix it.";      \
  echo >&2 ;                                                      \
  /bin/false)
    unset sub_make_done; ./scripts/install.sh

It is not an error. Make just showed the recipe lines it has executed,
but people may think that 'make install' has failed.

Likewise, the combination of V=1 and O= shows confusing
"*** The source tree is not clean, please run 'make mrproper'".

Suppress such misleading logs.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Modpost generates .vmlinux.export.c and *.mod.c, which are prerequisites
of vmlinux and modules, respectively.

The modpost stage should be re-run when the modpost code is updated.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Currently, modpost is executed twice; first for vmlinux, second
for modules.

This commit merges them.

Current build flow
==================

  1) build obj-y and obj-m objects
    2) link vmlinux.o
      3) modpost for vmlinux
        4) link vmlinux
          5) modpost for modules
            6) link modules (*.ko)

The build steps 1) through 6) are serialized, that is, modules are
built after vmlinux. You do not get benefits of parallel builds when
scripts/link-vmlinux.sh is being run.

New build flow
==============

  1) build obj-y and obj-m objects
    2) link vmlinux.o
      3) modpost for vmlinux and modules
        4a) link vmlinux
        4b) link modules (*.ko)

In the new build flow, modpost is invoked just once.

vmlinux and modules are built in parallel. One exception is
CONFIG_DEBUG_INFO_BTF_MODULES=y, where modules depend on vmlinux.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Move the build rules of vmlinux.o out of scripts/link-vmlinux.sh to
clearly separate 1) pre-modpost, 2) modpost, 3) post-modpost stages.
This will make further refactoring possible.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

.vmlinux.objs is used by modpost, so scripts/Makefile.modpost is
a better place to generate it.

It is used only when CONFIG_MODVERSIONS=y. It should be guarded
by "ifdef CONFIG_MODVERSIONS".
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Use the ordinary obj-y syntax to list subdirectories.

Note1:
Previously, the link order of lib-y depended on CONFIG_MODULES; lib-y
was linked before drivers-y when CONFIG_MODULES=y, otherwise after
drivers-y. This was a bug of commit 7273ad2b ("kbuild: link lib-y
objects to vmlinux forcibly when CONFIG_MODULES=y"), but it was not a
big deal after all. Now, all objects listed in lib-y are linked last,
irrespective of CONFIG_MODULES.

Note2:
Finally, the single target build in arch/*/lib/ works correctly. There was
a bug report about this. [1]

  $ make ARCH=arm arch/arm/lib/findbit.o
    CALL    scripts/checksyscalls.sh
    AS      arch/arm/lib/findbit.o

[1]: https://lore.kernel.org/linux-kbuild/YvUQOwL6lD4%2F5%2FU6@shell.armlinux.org.uk/Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

cc-ifversion is GCC specific. Replace it with compiler specific
variants. Update the users of cc-ifversion to use these new macros.

Link: https://github.com/ClangBuiltLinux/linux/issues/350
Link: https://lore.kernel.org/llvm/CAGG=3QWSAUakO42kubrCap8fp-gm1ERJJAYXTnP1iHk_wrH=BQ@mail.gmail.com/Suggested-by: Bill Wendling <morbo@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Doing make V=1 binrpm-pkg results in:

 Executing(%install): /bin/sh -e /var/tmp/rpm-tmp.EgV6qJ
 + umask 022
 + cd .
 + /bin/rm -rf /home/scgl/rpmbuild/BUILDROOT/kernel-6.0.0_rc5+-1.s390x
 + /bin/mkdir -p /home/scgl/rpmbuild/BUILDROOT
 + /bin/mkdir /home/scgl/rpmbuild/BUILDROOT/kernel-6.0.0_rc5+-1.s390x
 + mkdir -p /home/scgl/rpmbuild/BUILDROOT/kernel-6.0.0_rc5+-1.s390x/boot
 + make -f ./Makefile image_name
 + cp test -e include/generated/autoconf.h -a -e include/config/auto.conf || ( \ echo >&2; \ echo >&2 " ERROR: Kernel configuration is invalid."; \ echo >&2 " include/generated/autoconf.h or include/config/auto.conf are missing.";\ echo >&2 " Run 'make oldconfig && make prepare' on kernel src to fix it."; \ echo >&2 ; \ /bin/false) arch/s390/boot/bzImage /home/scgl/rpmbuild/BUILDROOT/kernel-6.0.0_rc5+-1.s390x/boot/vmlinuz-6.0.0-rc5+
 cp: invalid option -- 'e'
 Try 'cp --help' for more information.
 error: Bad exit status from /var/tmp/rpm-tmp.EgV6qJ (%install)

Because the make call to get the image name is verbose and prints
additional information.

Fixes: 993bdde9 ("kbuild: add image_name to no-sync-config-targets")
Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Remove unused function argument, and there is
no logic changes.
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

sym_set_choice_value could be removed and directly call
sym_set_tristate_value instead.
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Since commit 7b453719 ("kbuild: link symbol CRCs at final link,
removing CONFIG_MODULE_REL_CRCS"), the module versioning on the
(non-upstreamed-yet) kvx Linux port is broken due to unexpected padding
for __crc_* symbols. The kvx GCC adds padding so u32 gets 8-byte
alignment instead of 4.

I do not know if this happens for upstream architectures in general,
but any compiler has the freedom to insert padding for faster access.

Use the inline assembler to directly specify the wanted data layout.
This is how we previously did before the breakage.

Link: https://lore.kernel.org/lkml/20220817161438.32039-1-ysionneau@kalray.eu/
Link: https://lore.kernel.org/linux-kbuild/31ce5305-a76b-13d7-ea55-afca82c46cf2@kalray.eu/
Fixes: 7b453719 ("kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS")
Reported-by: Yann Sionneau <ysionneau@kalray.eu>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Yann Sionneau <ysionneau@kalray.eu>

Based on Linus' patch. Refactor scripts/Makefile.vmlinux_o as well.

Link: https://lore.kernel.org/lkml/CAHk-=wgjTMQgiKzBZTmb=uWGDEQxDdyF1+qxBkODYciuNsmwnw@mail.gmail.com/Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

The single target build has a subtle bug for the combination for
an individual file and a subdirectory.

[1] 'make kernel/fork.i' builds only kernel/fork.i

  $ make kernel/fork.i
    CALL    scripts/checksyscalls.sh
    DESCEND objtool
    CPP     kernel/fork.i

[2] 'make kernel/' builds only under the kernel/ directory.

  $ make kernel/
    CALL    scripts/checksyscalls.sh
    DESCEND objtool
    CC      kernel/fork.o
    CC      kernel/exec_domain.o
       [snip]
    CC      kernel/rseq.o
    AR      kernel/built-in.a

But, if you try to do [1] and [2] in a single command, you will get
only [1] with a weird log:

  $ make kernel/fork.i kernel/
    CALL    scripts/checksyscalls.sh
    DESCEND objtool
    CPP     kernel/fork.i
  make[2]: Nothing to be done for 'kernel/'.

With 'make kernel/fork.i kernel/', you should get both [1] and [2].

Rewrite the single target build.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Remove the bash build dependency for those who otherwise do not
have it installed. This also provides a significant speedup:

$ make defconfig
$ make yes2modconfig

...

$ find  .  -name "*.o" | grep -v vmlinux | wc
     3169      3169     89615
$ export NM=nm
$ time sh -c 'find . -name "*.o" | grep -v vmlinux | xargs -n1
./scripts/check-local-export'

Without patch:
    0m15.90s real     0m12.17s user     0m05.28s system

With patch:
dash + nawk
    0m02.16s real     0m02.92s user     0m00.34s system

dash + busybox awk
    0m02.36s real     0m03.36s user     0m00.34s system

dash + gawk
    0m02.07s real     0m03.26s user     0m00.32s system

bash + gawk
    0m03.55s real     0m05.00s user     0m00.54s system
Signed-off-by: Owen Rafferty <owen@owenrafferty.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

This reverts commit [1] in the pre-git era.

I do not know what problem happened in the script when sh != bash
because there is no commit message.

Now that this script is much simpler than it used to be, let's revert
it, and let' see. (If this turns out to be problematic, fix the code
with proper commit description.)

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=11acbbbb8a50f4de7dbe4bc1b5acc440dfe81810Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Minimize the scope of LC_ALL=C like before commit 87c94bfb ("kbuild:
override build timestamp & version").

Give LC_ALL=C to '$LD -v' to get the consistent version output, as commit
bcbcf50f ("kbuild: fix ld-version.sh to not be affected by locale")
mentioned the LD version is affected by locale.

While I was here, I merged two sed invocations.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Now that UTS_VERSION was separated out, this header can be generated
much earlier, and probably the top Makefile is a better place to do it
than init/Makefile.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Kbuild builds init/built-in.a twice; first during the ordinary
directory descending, second from scripts/link-vmlinux.sh.

We do this because UTS_VERSION contains the build version and the
timestamp. We cannot update it during the normal directory traversal
since we do not yet know if we need to update vmlinux. UTS_VERSION is
temporarily calculated, but omitted from the update check. Otherwise,
vmlinux would be rebuilt every time.

When Kbuild results in running link-vmlinux.sh, it increments the
version number in the .version file and takes the timestamp at that
time to really fix UTS_VERSION.

However, updating the same file twice is a footgun. To avoid nasty
timestamp issues, all build artifacts that depend on init/built-in.a
are atomically generated in link-vmlinux.sh, where some of them do not
need rebuilding.

To fix this issue, this commit changes as follows:

[1] Split UTS_VERSION out to include/generated/utsversion.h from
    include/generated/compile.h

    include/generated/utsversion.h is generated just before the
    vmlinux link. It is generated under include/generated/ because
    some decompressors (s390, x86) use UTS_VERSION.

[2] Split init_uts_ns and linux_banner out to init/version-timestamp.c
    from init/version.c

    init_uts_ns and linux_banner contain UTS_VERSION. During the ordinary
    directory descending, they are compiled with __weak and used to
    determine if vmlinux needs relinking. Just before the vmlinux link,
    they are compiled without __weak to embed the real version and
    timestamp.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

This is unneeded since commit 073a9ecb ("init/version.c: remove
Version_<LINUX_VERSION_CODE> symbol").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Unify the code between in-tree builds and external module builds.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Remove the potentially invalid modules.order instead of using
the temporary file.

Also, KBUILD_MODULES is don't care for single builds. No need to
cancel it.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The dependency, "modules: modules_check" is specified twice.
Commit 1a998be6 ("kbuild: check module name conflict for external
modules as well") missed to clean it up.

'PHONY += modules' also appears twice.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Use obj-y to clean up Makefile.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The AWK code was added to deduplicate modules.order in case $(obj-m)
contains the same module multiple times, but it is actually unneeded
since commit b2c88554 ("kbuild: update modules.order only when
contained modules are updated").

The list is already deduplicated before being processed by AWK because
$^ is the deduplicated list of prerequisites.
(Please note the real-prereqs macro uses $^)

Yet, modules.order will contain duplication if two different Makefiles
build the same module:

  foo/Makefile:

      obj-m += bar/baz.o

  foo/bar/Makefile:

      obj-m += baz.o

However, the parallel builds cannot properly handle this case in the
first place. So, it is better to let it fail (as already done by
scripts/modules-check.sh).
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

It is unneeded to check the sha1sum every time.

Create the timestamp files to manage it.

Add '.' to clean-dirs because 'make clean' must visit ./Kbuild to
clean up the timestamp files.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

My future plan is to list subdirectories in ./Kbuild. When it occurs,
$(vmlinux-alldirs) will not contain all subdirectories.

Let's hard-code the directory list until I get around to implementing
a more sophisticated way for generating a source tarball.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

missing-syscalls and old-atomics are meant to be phony targets.
Adding them to always-y is odd. (always-y should generate something).

Add a new phony target 'prepare', which depends on all the other.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

When receiving some signal, GNU Make automatically deletes the target if
it has already been changed by the interrupted recipe.

If the target is possibly incomplete due to interruption, it must be
deleted so that it will be remade from scratch on the next run of make.
Otherwise, the target would remain corrupted permanently because its
timestamp had already been updated.

Thanks to this behavior of Make, you can stop the build any time by
pressing Ctrl-C, and just run 'make' to resume it.

Kbuild also relies on this feature, but it is equivalently important
for any build systems that make decisions based on timestamps (if you
want to support Ctrl-C reliably).

However, this does not always work as claimed; Make immediately dies
with Ctrl-C if its stderr goes into a pipe.

  [Test Makefile]

    foo:
            echo hello > $@
            sleep 3
            echo world >> $@

  [Test Result]

    $ make                         # hit Ctrl-C
    echo hello > foo
    sleep 3
    ^Cmake: *** Deleting file 'foo'
    make: *** [Makefile:3: foo] Interrupt

    $ make 2>&1 | cat              # hit Ctrl-C
    echo hello > foo
    sleep 3
    ^C$                            # 'foo' is often left-over

The reason is because SIGINT is sent to the entire process group.
In this example, SIGINT kills 'cat', and 'make' writes the message to
the closed pipe, then dies with SIGPIPE before cleaning the target.

A typical bad scenario (as reported by [1], [2]) is to save build log
by using the 'tee' command:

    $ make 2>&1 | tee log

This can be problematic for any build systems based on Make, so I hope
it will be fixed in GNU Make. The maintainer of GNU Make stated this is
a long-standing issue and difficult to fix [3]. It has not been fixed
yet as of writing.

So, we cannot rely on Make cleaning the target. We can do it by
ourselves, in signal traps.

As far as I understand, Make takes care of SIGHUP, SIGINT, SIGQUIT, and
SITERM for the target removal. I added the traps for them, and also for
SIGPIPE just in case cmd_* rule prints something to stdout or stderr
(but I did not observe an actual case where SIGPIPE was triggered).

[Note 1]

The trap handler might be worth explaining.

    rm -f $@; trap - $(sig); kill -s $(sig) $$

This lets the shell kill itself by the signal it caught, so the parent
process can tell the child has exited on the signal. Generally, this is
a proper manner for handling signals, in case the calling program (like
Bash) may monitor WIFSIGNALED() and WTERMSIG() for WCE although this may
not be a big deal here because GNU Make handles SIGHUP, SIGINT, SIGQUIT
in WUE and SIGTERM in IUE.

  IUE - Immediate Unconditional Exit
  WUE - Wait and Unconditional Exit
  WCE - Wait and Cooperative Exit

For details, see "Proper handling of SIGINT/SIGQUIT" [4].

[Note 2]

Reverting 392885ee ("kbuild: let fixdep directly write to .*.cmd
files") would directly address [1], but it only saves if_changed_dep.
As reported in [2], all commands that use redirection can potentially
leave an empty (i.e. broken) target.

[Note 3]

Another (even safer) approach might be to always write to a temporary
file, and rename it to $@ at the end of the recipe.

   <command>  > $(tmp-target)
   mv $(tmp-target) $@

It would require a lot of Makefile changes, and result in ugly code,
so I did not take it.

[Note 4]

A little more thoughts about a pattern rule with multiple targets (or
a grouped target).

    %.x %.y: %.z
            <recipe>

When interrupted, GNU Make deletes both %.x and %.y, while this solution
only deletes $@. Probably, this is not a big deal. The next run of make
will execute the rule again to create $@ along with the other files.

[1]: https://lore.kernel.org/all/YLeot94yAaM4xbMY@gmail.com/
[2]: https://lore.kernel.org/all/20220510221333.2770571-1-robh@kernel.org/
[3]: https://lists.gnu.org/archive/html/help-make/2021-06/msg00001.html
[4]: https://www.cons.org/cracauer/sigint.html

Fixes: 392885ee ("kbuild: let fixdep directly write to .*.cmd files")
Reported-by: Ingo Molnar <mingo@kernel.org>
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>