For ARCH=um, ${CC} is used as the linker driver. Hence, the linker
options are prefixed with -Wl, .

Merge the similar code.

I replaced the -T option with the long option --script= so that it
works well with/without ${wl}.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

arch/um/Makefile passes the -f option to the ln command:

  linux: vmlinux
          @echo '  LINK $@'
          $(Q)ln -f $< $@

So, the hard link is always re-created, and the old one is removed
anyway.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

When Clang LTO is enabled, vmlinux_link() reuses vmlinux.o instead of
re-linking ${KBUILD_VMLINUX_OBJS} and ${KBUILD_VMLINUX_LIBS}.

That is the only difference here, so merge the similar code.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

cmd_update_lto_symversions merges all the existing *.symversions, but
some of them might be stale.

If the last EXPORT_SYMBOL is removed from a C file, the *.symversions
file is not deleted or updated. It contains stale CRCs, but still they
will be used for linking the vmlinux or modules.

It is not a big deal when the EXPORT_SYMBOL is really removed. However,
when the EXPORT_SYMBOL is moved to another file, the same __crc_<symbol>
will appear twice in the merged *.symversions, possibly with different
CRCs if the function argument is changed at the same time. It would
confuse module versioning.

If no EXPORT_SYMBOL is found, let's remove *.symversions explicitly.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

This is not used anywhere because the short log is displayed when
it is used through a $(call cmd,...) invocation.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

The current gen_compile_commands.py assumes that objects are always
built by a single command.

It makes sense to support cases where objects are built by a series of
commands:

  cmd_<object> := <command1> ; <command2>

One use-case is that <command1> is a compiler command, and <command2>
an objtool command.

It allows *.cmd files to contain an objtool command so that any change
in it triggers object rebuilds.

If ; appears after the C source file, take the first command.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>

As noted in the comment, -mtune= has been supported since GCC 3.4. The
minimum required version of GCC to build the kernel (as specified in
Documentation/process/changes.rst) is GCC 4.9.

tune is not immediately expanded. Instead it defines a macro that will
test via cc-option later values for -mtune=. But we can skip the test
whether to use -mtune= vs. -mcpu=.
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

cc-option-yn can be replaced with cc-option. ie.
Checking for support:
ifeq ($(call cc-option-yn,$(FLAG)),y)
becomes:
ifneq ($(call cc-option,$(FLAG)),)

Checking for lack of support:
ifeq ($(call cc-option-yn,$(FLAG)),n)
becomes:
ifeq ($(call cc-option,$(FLAG)),)

This allows us to pursue removing cc-option-yn.
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

cc-option-yn can be replaced with cc-option. ie.
Checking for support:
ifeq ($(call cc-option-yn,$(FLAG)),y)
becomes:
ifneq ($(call cc-option,$(FLAG)),)

Checking for lack of support:
ifeq ($(call cc-option-yn,$(FLAG)),n)
becomes:
ifeq ($(call cc-option,$(FLAG)),)

This allows us to pursue removing cc-option-yn.
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

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

Currently, the install target in arch/sparc/Makefile descends into
arch/sparc/boot/Makefile to invoke the shell script, but there is no
good reason to do so.

arch/sparc/Makefile can run the shell script directly.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

All of these are unneeded. The directories to descend are specified
by obj-$(CONFIG_...).
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The sh arch has a install.sh script, but no Makefile actually calls it.
Remove it to keep anyone from accidentally calling it in the future.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

When CONFIG_TRIM_UNUSED_KSYMS is enabled, I see some warnings like this:

  nm: arch/x86/entry/vdso/vdso32/note.o: no symbols

$NM (both GNU nm and llvm-nm) warns when no symbol is found in the
object. Suppress the stderr.

Fangrui Song mentioned binutils>=2.37 `nm -q` can be used to suppress
"no symbols" [1], and llvm-nm>=13.0.0 supports -q as well.

We cannot use it for now, but note it as a TODO.

[1]: https://sourceware.org/bugzilla/show_bug.cgi?id=27408

Fixes: bbda5ec6 ("kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>

It has been brought up a few times in various code reviews that clang
3.5 introduced -f{,no-}integrated-as as the preferred way to enable and
disable the integrated assembler, mentioning that -{no-,}integrated-as
are now considered legacy flags.

Switch the kernel over to using those variants in case there is ever a
time where clang decides to remove the non-'f' variants of the flag.

Also, fix a typo in a comment ("intergrated" -> "integrated").

Link: https://releases.llvm.org/3.5.0/tools/clang/docs/ReleaseNotes.html#new-compiler-flagsReviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

-Wunused-but-set-variable and -Wunused-const-variable are both disabled
for the same reason but there is a blank line between them and no blank
line between -Wno-unused-const-variable and the block.

Shuffle the new line so that it is clear that the comment applied to
both flags and the next block is separate from them.
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Whenever a warning is disabled, it is helpful for future travelers to
understand why the warning is disabled and why it is acceptable to do
so. Add a comment for -Wno-gnu so that people understand why it is
disabled.
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Turning on -Wformat does not reveal any instances of this warning across
several different builds so remove this line to keep the number of
disabled warnings as slim as possible.

This has been disabled since commit 61163efa ("kbuild: LLVMLinux:
Add Kbuild support for building kernel with Clang"), which does not
explain exactly why it was turned off but since it was so long ago in
terms of both the kernel and LLVM so it is possible that some bug got
fixed along the way.
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

if_changed, if_changed_dep, and if_changed_rule must have FORCE as a
prerequisite so the command line change is detected.

Documentation/kbuild/makefiles.rst clearly explains it:

  Note: It is a typical mistake to forget the FORCE prerequisite.

However, not all people follow the document.

This mistake occurred again and again, so a compelling force is needed.

Show a warning if FORCE is missing in the prerequisite of if_changed
and friends. Same for filechk.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nicolas Schier <n.schier@avm.de>

Add a new macro that expands into $(newer-prereqs)$(cmd-check).

It makes it easier to add common code for if_changed, if_changed_dep,
and if_changed_rule.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Add FORCE so that if_changed can detect the command line change.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

With CONFIG_LTO_CLANG, we currently link modules into native
code just before modpost, which means with TRIM_UNUSED_KSYMS
enabled, we still look at the LLVM bitcode in the .o files when
generating the list of used symbols. As the bitcode doesn't
yet have calls to compiler intrinsics and llvm-nm doesn't see
function references that only exist in function-level inline
assembly, we currently need a whitelist for TRIM_UNUSED_KSYMS to
work with LTO.

This change moves module LTO linking to happen earlier, and
thus avoids the issue with LLVM bitcode and TRIM_UNUSED_KSYMS
entirely, allowing us to also drop the whitelist from
gen_autoksyms.sh.

Link: https://github.com/ClangBuiltLinux/linux/issues/1369Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Alexander Lobakin <alobakin@pm.me>
Tested-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

cc-option, cc-option-yn, and cc-disable-warning all invoke the compiler
during build time, and can slow down the build when these checks become
stale for our supported compilers, whose minimally supported versions
increases over time. See Documentation/process/changes.rst for the
current supported minimal versions (GCC 4.9+, clang 10.0.1+). Compiler
version support for these flags may be verified on godbolt.org.

The following flags are GCC only and supported since at least GCC 4.9.
Remove cc-option and cc-disable-warning tests.
* -fno-tree-loop-im
* -Wno-maybe-uninitialized
* -fno-reorder-blocks
* -fno-ipa-cp-clone
* -fno-partial-inlining
* -femit-struct-debug-baseonly
* -fno-inline-functions-called-once
* -fconserve-stack

The following flags are supported by all supported versions of GCC and
Clang. Remove their cc-option, cc-option-yn, and cc-disable-warning tests.
* -fno-delete-null-pointer-checks
* -fno-var-tracking
* -Wno-array-bounds

The following configs are made dependent on GCC, since they use GCC
specific flags.
* READABLE_ASM
* DEBUG_SECTION_MISMATCH

-mfentry was not supported by s390-linux-gnu-gcc until gcc-9+, add a
comment.

--param=allow-store-data-races=0 was renamed to -fno-allow-store-data-races
in the GCC 10 release; add a comment.

-Wmaybe-uninitialized (GCC specific) was being added for CONFIG_GCOV,
then again unconditionally; add it only once.

Also, base RETPOLINE_CFLAGS and RETPOLINE_VDSO_CFLAGS on CONFIC_CC_IS_*
then remove cc-option tests for Clang.

Link: https://github.com/ClangBuiltLinux/linux/issues/1436Acked-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Kees' post inspired me to get more involved. I still have a long way to
go in terms of mastery of GNU make, but at the least I can help with
more code review. It's also helpful for me to pick up on what's missing
from the LLVM ecosystem.

Link: https://security.googleblog.com/2021/08/linux-kernel-security-done-right.htmlSigned-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Ship minimal stdarg.h (1 type, 4 macros) as <linux/stdarg.h>.
stdarg.h is the only userspace header commonly used in the kernel.

GPL 2 version of <stdarg.h> can be extracted from
http://archive.debian.org/debian/pool/main/g/gcc-4.2/gcc-4.2_4.2.4.orig.tar.gzSigned-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Delete/fixup few includes in anticipation of global -isystem compile
option removal.

Note: crypto/aegis128-neon-inner.c keeps <stddef.h> due to redefinition
of uintptr_t error (one definition comes from <stddef.h>, another from
<linux/types.h>).
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

LLVM_IAS=1 controls enabling clang's integrated assembler via
-integrated-as. This was an explicit opt in until we could enable
assembler support in Clang for more architecures. Now we have support
and CI coverage of LLVM_IAS=1 for all architecures except a few more
bugs affecting s390 and powerpc.

This commit flips the default from opt in via LLVM_IAS=1 to opt out via
LLVM_IAS=0.  CI systems or developers that were previously doing builds
with CC=clang or LLVM=1 without explicitly setting LLVM_IAS must now
explicitly opt out via LLVM_IAS=0, otherwise they will be implicitly
opted-in.

This finally shortens the command line invocation when cross compiling
with LLVM to simply:

$ make ARCH=arm64 LLVM=1
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

LLVM_IAS is the user interface to set the -(no-)integrated-as flag,
and it should be used only for that purpose.

LLVM_IAS is checked in some places to determine the assembler type,
but it is not precise.

For example,

 $ make CC=gcc LLVM_IAS=1

... will use the GNU assembler (i.e. binutils) since LLVM_IAS=1 is
effective only when $(CC) is clang.

Of course, 'CC=gcc LLVM_IAS=1' is an odd combination, but the build
system can be more robust against such insane input.

Commit ba64beb1 ("kbuild: check the minimum assembler version in
Kconfig") introduced CONFIG_AS_IS_GNU/LLVM, which is more precise
because Kconfig checks the version string from the assembler in use.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>

As noted by Masahiro, document how we can generally infer CROSS_COMPILE
(and the more specific details about --target and --prefix) based on
ARCH.

Change use of env vars to command line parameters.
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

We get constant feedback that the command line invocation of make is too
long when compiling with LLVM. CROSS_COMPILE is helpful when a toolchain
has a prefix of the target triple, or is an absolute path outside of
$PATH.

Since a Clang binary is generally multi-targeted, we can infer a given
target from SRCARCH/ARCH.  If CROSS_COMPILE is not set, simply set
--target= for CLANG_FLAGS, KBUILD_CFLAGS, and KBUILD_AFLAGS based on
$SRCARCH.

Previously, we'd cross compile via:
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make LLVM=1 LLVM_IAS=1
Now:
$ ARCH=arm64 make LLVM=1 LLVM_IAS=1

For native builds (not involving cross compilation) we now explicitly
specify a target triple rather than rely on the implicit host triple.

Link: https://github.com/ClangBuiltLinux/linux/issues/1399Suggested-by: Arnd Bergmann <arnd@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Arnd Bergmann <arnd@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

With some of the changes we'd like to make to CROSS_COMPILE, the initial
block of clang flag handling which controls things like the target triple,
whether or not to use the integrated assembler and how to find GAS,
and erroring on unknown warnings is becoming unwieldy. Move it into its
own file under scripts/.
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

It is always safe to use the same compiler for the kernel and external
modules, but in reality, some distributions such as Fedora release a
different version of GCC from the one used for building the kernel.

There was a long discussion about mixing different compilers [1].

I do not repeat it here, but at least, showing a heads up in that
case is better than nothing.

Linus suggested [2]:
  And a warning might be more palatable even if different compiler
  version work fine together. Just a heads up on "it looks like you
  might be mixing compiler versions" is a valid note, and isn't
  necessarily wrong. Even when they work well together, maybe you want
  to have people at least _aware_ of it.

This commit shows a warning unless the compiler is exactly the same.

  warning: the compiler differs from the one used to build the kernel
    The kernel was built by: gcc (GCC) 11.1.1 20210531 (Red Hat 11.1.1-3)
    You are using:           gcc (GCC) 11.2.1 20210728 (Red Hat 11.2.1-1)

Check the difference, and if it is OK with you, please proceed at your
risk.

To avoid the locale issue as in commit bcbcf50f ("kbuild: fix
ld-version.sh to not be affected by locale"), pass LC_ALL=C to
"$(CC) --version".

[1] https://lore.kernel.org/linux-hardening/efe6b039a544da8215d5e54aa7c4b6d1986fc2b0.1611607264.git.jpoimboe@redhat.com/
[2] https://lore.kernel.org/lkml/CAHk-=wgjwhDy-y4mQh34L+2aF=n6BjzHdqAW2=8wri5x7O04pA@mail.gmail.com/Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Set the x bit to some scripts to make them directly executable.

Especially, scripts/checkdeclares.pl is not hooked by anyone.
It should be executable since it is tedious to type
'perl scripts/checkdeclares.pl'.

The original patch [1] set the x bit properly, but it was lost when
it was merged as commit 21917bde ("scripts: a new script for
checking duplicate struct declaration").

[1] https://lore.kernel.org/lkml/20210401110943.1010796-1-wanjiabing@vivo.com/Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

As explained in commit 3204a7fb ("kbuild: prefix $(srctree)/ to some
included Makefiles"), I want to stop using --include-dir some day.

I already fixed up the top Makefile, but some arch Makefiles (mips, um,
x86) still include check-in Makefiles without $(srctree)/.

Fix them up so 'need-sub-make := 1' can go away for this case.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

When merging configuration fragments, it might be of interest to
identify mismatches (redefinitions) programmatically. Hence add the
option -s (strict mode) to instruct merge_config.sh to bail out in
case any redefinition has been detected.

With strict mode, warnings are emitted as before, but the script
terminates with rc=1. If -y is set to define "builtin having
precedence over modules", fragments are still allowed to set =m (while
the base config has =y). Strict mode will tolerate that as demotions
from =y to =m are ignored when setting -y.
Signed-off-by: Matthias Maennich <maennich@google.com>
Reviewed-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Pull timer fix from Thomas Gleixner:
 "A single timer fix:

   - Prevent a memory ordering issue in the timer expiry code which
     makes it possible to observe falsely that the callback has been
     executed already while that's not the case, which violates the
     guarantee of del_timer_sync()"

* tag 'timers-urgent-2021-08-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timers: Move clearing of base::timer_running under base:: Lock

Pull scheduler fix from Thomas Gleixner:
 "A single scheduler fix:

   - Prevent a double enqueue caused by rt_effective_prio() being
     invoked twice in __sched_setscheduler()"

* tag 'sched-urgent-2021-08-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/rt: Fix double enqueue caused by rt_effective_prio

Pull perf fixes from Thomas Gleixner:
 "A set of perf fixes:

   - Correct the permission checks for perf event which send SIGTRAP to
     a different process and clean up that code to be more readable.

   - Prevent an out of bound MSR access in the x86 perf code which
     happened due to an incomplete limiting to the actually available
     hardware counters.

   - Prevent access to the AMD64_EVENTSEL_HOSTONLY bit when running
     inside a guest.

   - Handle small core counter re-enabling correctly by issuing an ACK
     right before reenabling it to prevent a stale PEBS record being
     kept around"

* tag 'perf-urgent-2021-08-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/x86/intel: Apply mid ACK for small core
  perf/x86/amd: Don't touch the AMD64_EVENTSEL_HOSTONLY bit inside the guest
  perf/x86: Fix out of bound MSR access
  perf: Refactor permissions check into perf_check_permission()
  perf: Fix required permissions if sigtrap is requested

Pull char/misc driver fixes from Greg KH:
 "Here are some small char/misc driver fixes for 5.14-rc5.

  They resolve a few regressions that people reported:

   - acrn driver fix

   - fpga driver fix

   - interconnect tiny driver fixes

  All have been in linux-next for a while with no reported issues"

* tag 'char-misc-5.14-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
  interconnect: Fix undersized devress_alloc allocation
  interconnect: qcom: icc-rpmh: Add BCMs to commit list in pre_aggregate
  interconnect: qcom: icc-rpmh: Ensure floor BW is enforced for all nodes
  fpga: dfl: fme: Fix cpu hotplug issue in performance reporting
  virt: acrn: Do hcall_destroy_vm() before resource release
  interconnect: Always call pre_aggregate before aggregate
  interconnect: Zero initial BW after sync-state