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git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux
Pull Kbuild fixes from Nathan Chancellor:
- Move probing of '-mfentry' back into Makefile instead of Kconfig
because it does not interact well with toolchains that support
multiple bit widths
- Add a big comment in scripts/Kconfig.toolchain of two pitfalls when
moving cc-option checks from Kbuild to Kconfig
* tag 'kbuild-fixes-7.4-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux:
scripts/Kconfig.toolchain: Highlight cc-option differences between Kconfig and Kbuild
kbuild: Move testing of '-mfentry' back to Makefile from Kconfig
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git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux
Pull Kbuild / Kconfig updates from Nathan Chancellor:
"Kbuild:
- Suppress compiler flags in debug info for external module builds
- Use '-fmacro-prefix-map' in more places in the build
- Merge initial set of changes from Lorenzo's speed up series, along
with some fixes found through testing:
- Avoid allocating .modinfo in vmlinux
- Speed up kallsyms by indexing symbols by token and outputting
binary data to disk directly then including in assembly via
.incbin
- Don't sort $(NM) output when unnecessary
- Only emit relocations on the final vmlinx link
- Reimplement mksysmap in C
- Move many cc-option and ld-option calls into the Kconfig stage to
cache their results
- Use pigz for gzip compression when available
- Move gen_init_cpio and gen_initramfs.sh from usr/ to scripts/
- Add a TOML configuration to scripts/container and update
documentation accordingly
- Add a generic, opt-in mechanism for checking that headers can
compile standalone
- Update machine function splitting argument for LLVM 24 rename in
AutoFDO build
- Miscellaneous minor clean ups, fixes, and hardening, mostly
found/fixed via LLMs
Kconfig:
- Turn recursive ranges into an error
- Fix savedefconfig for defaults that were adjusted for being out of
range and revert a previously applied workaround
- Improvements and hardening around integer and hexadecimal values
- Emit a warning when selecting or implying a choice symbol, which
has no effect
- Emit a warning when KCONFIG_PROBABILITY is malformed
- Introduce def_string / def_int / def_hex to mirror the existing
def_bool / def_tristate to succinctly set a value and type at the
same time.
- Add cc-option-str and ld-option-str macros to act like Kbuild's
cc-option and ld-option, returning the string when the option is
supported, allowing many checks to be moved into Kconfig
- Minor usability improvements to Kconfig tests"
* tag 'kbuild-7.4-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux: (59 commits)
kbuild: AutoFDO: Update split machine function argument for upstream rename
kbuild: Mark the initcall ordering recipe as recursive
kbuild: Mark the gzip recipes as recursive
localmodconfig: Explicitly report boolean configs during integrity check
scripts/make_fit: Ignore schema checks when decomposing DTBs
clang-tools: Import os for broken pipe handling
kconfig: use the value argument in sym_get_near_range_bound()
kconfig: fix infinite loop in conf_choice() when no choice value is visible
kconfig: cleanup stale comment about 'keys' array
kconfig: Improve ergonomics around disabling warnings with cc-option
scripts/Kconfig.toolchain: Drop compiler symbols from dependencies
checkkconfigsymbols.py: Parse Git status output line by line
gen_init_cpio: stop parsing on lines with a missing argument list
.gitignore: drop Module.markers
.gitignore: ignore pacman package signatures
kbuild: add header check facility as a manually run static analyzer
Documentation: dev-tools: refer to user ID rather than id
Documentation: dev-tools: update container.rst with config file
scripts: add TOML config to container tool
kconfig: tests: {old,save}defconfig: Forward dynamic keyword arguments
...
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and Kbuild
Performing cc-option checks in Kconfig instead of Kbuild can help speed
up incremental builds where the configuration does not change, as the
results of the probes can be easily cached. However, there are two
potential issues that folks need to consider when using cc-option in
Kconfig compared to Kbuild.
The first is that in Kbuild, cc-option additions are cumulative, so
KBUILD_CFLAGS += $(call cc-option,-mfoo)
KBUILD_CFLAGS += $(call cc-option,-mbar)
results in '-mbar' being tested with '-mfoo' if it was supported. In
Kconfig, '-mbar' would be tested without '-mfoo', which could change the
result if '-mbar' depends on '-mfoo' being present, so it would need to
test support with
$(cc-option,-mbar -mfoo)
The second is that the Kconfig stage is where questions like "is the
target architecture 32-bit or 64-bit" or "is the target architecture big
or little endian" are answered, which very much matters for testing
compiler options. Toolchains may be configured for either option, so the
kernel needs to pass compiler flags like '-m32', '-m64',
'-mlittle-endian', and '-mbig-endian' to properly match a user's
configuration choices. Without these flags, '-mfoo' is tested against a
toolchain's configured default, resulting in an inconsistent answer to
whether the flag is actually supported for the requested configuration.
This could manifest as a build breakage from an unexpectedly included
but unsupported flag or missing functionality from an unexpected omitted
flag.
Add a big comment summarizing these two issues to help future travelers.
Link: https://patch.msgid.link/20261020-kconfig-fix-mfentry-check-v1-2-428258bc0fc0@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
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Unlike cc-option in Kbuild, cc-option in Kconfig does not test options
with either bit ('-m32' / '-m64') or endianness ('-mbig-endian' /
'-mlittle-endian') flags because which flag to use may depend on the
result of the configuration stage. This difference changes the result of
testing for '-mfentry' support when using the kernel.org s390 cross
compiler, which is configured for 32-bit by default.
$ s390-linux-gcc -mfentry -o /dev/null -x c -c /dev/null
cc1: error: '-mfentry' is supported only for 64-bit CPUs
arch/s390/Makefile sets '-m64' in KBUILD_CPPFLAGS early, so '-mfentry'
support was properly tested before the move to Kconfig.
$ s390-linux-gcc -m64 -mfentry -o /dev/null -x c -c /dev/null
Ricardo reported another issue with moving this check from Kbuild to
Kconfig, as '-mfentry' is not supported for x86_32 without '-fno-pic',
which affects GCC builds that are configured with PIE enabled by
default. arch/x86/Makefile adds '-fno-pic' to KBUILD_CFLAGS, so this
works properly in Kbuild.
Move the '-mfentry' check back into Kbuild to avoid adding additional
complexity to the Kconfig entry.
Fixes: 454e00cf8ee5 ("kbuild: avoid re-running compiler and linker probes")
Reported-by: Ricardo Ribalda <ribalda@chromium.org>
Closes: https://lore.kernel.org/20261020-pie-v1-1-9be09f2324b1@chromium.org/
Link: https://patch.msgid.link/20261020-kconfig-fix-mfentry-check-v1-1-428258bc0fc0@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
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This is essentially a port of commit 550ccb178de2 ("Make 'cc-option'
work correctly for the -Wno-xyzzy pattern") to scripts/Kconfig.include,
which simplifies the definition of many of the newly added CC_OPT_WNO_
symbols in scripts/Kconfig.toolchain and matches cc-option's behavior in
Kbuild.
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20261007-scripts-kconfig-toolchain-improvements-v1-2-1e524178da11@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
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Commit 454e00cf8ee5 ("kbuild: avoid re-running compiler and linker
probes") moved many cc-option calls from the main Makefile into Kconfig.
In the process, code such as
ifdef CONFIG_CC_IS_GCC
KBUILD_CFLAGS += $(call cc-option,-foo)
endif
was converted into Kconfig as
config CC_OPT_FOO
def_string "$(cc-option-str,-foo)" if CC_IS_GCC
The 'if CC_IS_GCC' is generally unnecessary because it does not prevent
the cc-option-str call from running (which is the primary reason the
ifdef guards exists in the Makefile), as cc-option-str and the like are
run before Kconfig even parses the dependency. It only impacts the
symbol's visibility, which does not really matter in the general case,
so remove these dependencies.
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20261007-scripts-kconfig-toolchain-improvements-v1-1-1e524178da11@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
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Each kernel make invocation begins with ~30 compiler and linker runs each
of which performs duplicate probe for a number of compiler and linker
options.
This is useless work - the compiler and its version is known, so use these
to determine which options are available, once.
Using the newly introduced cc-option-str, track the result of each probe in
CC_OPT_*, LD_OPT_* variables and have Makefile's simply append the symbol.
Some care has to be taken around negative options, i.e. -Wno-xxx, as gcc
accepts an unknown -Wno- without complaint and only complains later, so
instead probe the positive form for these cases.
Use CC_HAS_* For those probes that gate a Makefile conditional rather than
a simple option, as per the established pattern for this.
This change avoids a subtle issue with ppc32 (big endian) - clang doesn't
accept -fno-stack-clash-protection on this sub-target, so keep this option
in the Makefile.
With gcc and clang, defconfig and allmodconfig, the recorded command
lines are unchanged, a build with nothing to do rebuilds nothing and W=1
continues to function correctly.
Doing this improves all builds, but has a particularly positive impact on
no-op builds (builds where nothing has changed).
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, no-op make, gcc 0.78s 0.60s -0.18s (-23%)
x86 defconfig, no-op make, clang 0.94s 0.66s -0.28s (-30%)
x86 defconfig, touch mm/vma.c, gcc 8.6s 8.5s -0.16s (-2%)
x86 defconfig, touch mm/vma.c, clang 8.0s 7.7s -0.24s (-3%)
x86 defconfig, clean, clang 29.8s 29.4s -0.37s (-1%)
x86 allmodconfig, no-op make, gcc 12.9s 12.7s -0.23s (-2%)
x86 allmodconfig, no-op make, clang 14.2s 13.9s -0.29s (-2%)
x86 allmodconfig, touch mm/vma.c, clang 32.2s 31.9s -0.30s (-1%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Link: https://patch.msgid.link/20260923-build-speedup-v4-12-73128809a4a4@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
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init/Kconfig opens with two hundred lines identifying the compiler,
assembler, linker and rustc and probing which options they support, none of
it to do with init.
Move them into their own file, sourced from the top of init/Kconfig, so
that the next commit can add to them without growing init/Kconfig further.
Also update MAINTAINERS to put the new file in the KCONFIG entry.
No functional change intended.
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Link: https://patch.msgid.link/20260923-build-speedup-v4-11-73128809a4a4@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
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