kernel/linux.git/Kbuild, branch master

checksyscalls: move instance functionality into generic code

2026-04-05T07:21:32+00:00

On MIPS the checksyscalls.sh script may be executed multiple times. Currently these multiple executions are executed on each build as kbuild see that the commands have changed each time. Use a dedicated stamp file for each different invocation to avoid the spurious executions. Signed-off-by: Thomas Weißschuh Acked-by: Arnd Bergmann Reviewed-by: Nicolas Schier Link: https://patch.msgid.link/20260402-kbuild-missing-syscalls-v3-3-6641be1de2db@weissschuh.net Signed-off-by: Nicolas Schier

checksyscalls: only run when necessary

2026-04-05T07:21:31+00:00

Currently checksyscalls.sh is unconditionally executed during each build. Most of these executions are unnecessary. Only run checksyscalls.sh if one of its inputs have changed. This new logic does not work for the multiple invocations done for MIPS. The effect is that checksyscalls.sh is still executed unconditionally. However this is not worse than before. Signed-off-by: Thomas Weißschuh Acked-by: Arnd Bergmann Reviewed-by: Nicolas Schier Link: https://patch.msgid.link/20260402-kbuild-missing-syscalls-v3-2-6641be1de2db@weissschuh.net Signed-off-by: Nicolas Schier

sched: Make migrate_{en,dis}able() inline

2025-09-25T07:57:16+00:00

For now, migrate_enable and migrate_disable are global, which makes them become hotspots in some case. Take BPF for example, the function calling to migrate_enable and migrate_disable in BPF trampoline can introduce significant overhead, and following is the 'perf top' of FENTRY's benchmark (./tools/testing/selftests/bpf/bench trig-fentry): 54.63% bpf_prog_2dcccf652aac1793_bench_trigger_fentry [k] bpf_prog_2dcccf652aac1793_bench_trigger_fentry 10.43% [kernel] [k] migrate_enable 10.07% bpf_trampoline_6442517037 [k] bpf_trampoline_6442517037 8.06% [kernel] [k] __bpf_prog_exit_recur 4.11% libc.so.6 [.] syscall 2.15% [kernel] [k] entry_SYSCALL_64 1.48% [kernel] [k] memchr_inv 1.32% [kernel] [k] fput 1.16% [kernel] [k] _copy_to_user 0.73% [kernel] [k] bpf_prog_test_run_raw_tp So in this commit, we make migrate_enable/migrate_disable inline to obtain better performance. The struct rq is defined internally in kernel/sched/sched.h, and the field "nr_pinned" is accessed in migrate_enable/migrate_disable, which makes it hard to make them inline. Alexei Starovoitov suggests to generate the offset of "nr_pinned" in [1], so we can define the migrate_enable/migrate_disable in include/linux/sched.h and access "this_rq()->nr_pinned" with "(void *)this_rq() + RQ_nr_pinned". The offset of "nr_pinned" is generated in include/generated/rq-offsets.h by kernel/sched/rq-offsets.c. Generally speaking, we move the definition of migrate_enable and migrate_disable to include/linux/sched.h from kernel/sched/core.c. The calling to __set_cpus_allowed_ptr() is leaved in ___migrate_enable(). The "struct rq" is not available in include/linux/sched.h, so we can't access the "runqueues" with this_cpu_ptr(), as the compilation will fail in this_cpu_ptr() -> raw_cpu_ptr() -> __verify_pcpu_ptr(): typeof((ptr) + 0) So we introduce the this_rq_raw() and access the runqueues with arch_raw_cpu_ptr/PERCPU_PTR directly. The variable "runqueues" is not visible in the kernel modules, and export it is not a good idea. As Peter Zijlstra advised in [2], we define and export migrate_enable/migrate_disable in kernel/sched/core.c too, and use them for the modules. Before this patch, the performance of BPF FENTRY is: fentry : 113.030 ± 0.149M/s fentry : 112.501 ± 0.187M/s fentry : 112.828 ± 0.267M/s fentry : 115.287 ± 0.241M/s After this patch, the performance of BPF FENTRY increases to: fentry : 143.644 ± 0.670M/s fentry : 149.764 ± 0.362M/s fentry : 149.642 ± 0.156M/s fentry : 145.263 ± 0.221M/s Signed-off-by: Menglong Dong Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/bpf/CAADnVQ+5sEDKHdsJY5ZsfGDO_1SEhhQWHrt2SMBG5SYyQ+jt7w@mail.gmail.com/ [1] Link: https://lore.kernel.org/all/20250819123214.GH4067720@noisy.programming.kicks-ass.net/ [2]

drm: ensure drm headers are self-contained and pass kernel-doc

2025-02-12T08:44:43+00:00

Ensure drm headers build, are self-contained, have header guards, and have no kernel-doc warnings, when CONFIG_DRM_HEADER_TEST=y. The mechanism follows similar patters used in i915, xe, and usr/include. To cover include/drm, we need to recurse there using the top level Kbuild and the new include/Kbuild files. v4: check for CONFIG_WERROR in addition to CONFIG_DRM_WERROR v3: adapt to upstream build changes v2: make DRM_HEADER_TEST depend on DRM Suggested-by: Daniel Vetter Cc: David Airlie Cc: Daniel Vetter Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: Masahiro Yamada Acked-by: Thomas Zimmermann Acked-by: Simona Vetter Link: https://patchwork.freedesktop.org/patch/msgid/d8ad1c6d707f38a55987f616cb9650aef30b84e1.1737556766.git.jani.nikula@intel.com Signed-off-by: Jani Nikula

Merge tag 'kbuild-v6.1' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild

2022-10-10T19:00:45+00:00

Pull Kbuild updates from Masahiro Yamada: - Remove potentially incomplete targets when Kbuid is interrupted by SIGINT etc in case GNU Make may miss to do that when stderr is piped to another program. - Rewrite the single target build so it works more correctly. - Fix rpm-pkg builds with V=1. - List top-level subdirectories in ./Kbuild. - Ignore auto-generated __kstrtab_* and __kstrtabns_* symbols in kallsyms. - Avoid two different modules in lib/zstd/ having shared code, which potentially causes building the common code as build-in and modular back-and-forth. - Unify two modpost invocations to optimize the build process. - Remove head-y syntax in favor of linker scripts for placing particular sections in the head of vmlinux. - Bump the minimal GNU Make version to 3.82. - Clean up misc Makefiles and scripts. * tag 'kbuild-v6.1' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (41 commits) docs: bump minimal GNU Make version to 3.82 ia64: simplify esi object addition in Makefile Revert "kbuild: Check if linker supports the -X option" kbuild: rebuild .vmlinux.export.o when its prerequisite is updated kbuild: move modules.builtin(.modinfo) rules to Makefile.vmlinux_o zstd: Fixing mixed module-builtin objects kallsyms: ignore __kstrtab_* and __kstrtabns_* symbols kallsyms: take the input file instead of reading stdin kallsyms: drop duplicated ignore patterns from kallsyms.c kbuild: reuse mksysmap output for kallsyms mksysmap: update comment about __crc_* kbuild: remove head-y syntax kbuild: use obj-y instead extra-y for objects placed at the head kbuild: hide error checker logs for V=1 builds kbuild: re-run modpost when it is updated kbuild: unify two modpost invocations kbuild: move vmlinux.o rule to the top Makefile kbuild: move .vmlinux.objs rule to Makefile.modpost kbuild: list sub-directories in ./Kbuild Makefile.compiler: replace cc-ifversion with compiler-specific macros ...

kbuild: list sub-directories in ./Kbuild

2022-09-28T19:41:31+00:00

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 7273ad2b08f8 ("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 Tested-by: Nick Desaulniers Reviewed-by: Nicolas Schier

kbuild: check sha1sum just once for each atomic header

2022-09-28T19:40:14+00:00

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

kbuild: add phony targets to ./Kbuild

2022-09-28T17:00:29+00:00

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

kbuild: rename hostprogs-y/always to hostprogs/always-y

2020-02-03T16:53:07+00:00

In old days, the "host-progs" syntax was used for specifying host programs. It was renamed to the current "hostprogs-y" in 2004. It is typically useful in scripts/Makefile because it allows Kbuild to selectively compile host programs based on the kernel configuration. This commit renames like follows: always -> always-y hostprogs-y -> hostprogs So, scripts/Makefile will look like this: always-$(CONFIG_BUILD_BIN2C) += ... always-$(CONFIG_KALLSYMS) += ... ... hostprogs := $(always-y) $(always-m) I think this makes more sense because a host program is always a host program, irrespective of the kernel configuration. We want to specify which ones to compile by CONFIG options, so always-y will be handier. The "always", "hostprogs-y", "hostprogs-m" will be kept for backward compatibility for a while. Signed-off-by: Masahiro Yamada

kbuild: do not descend to ./Kbuild when cleaning

2019-08-21T12:03:58+00:00

'make clean' descends into ./Kbuild, but does not clean anything since everything is added to no-clean-files. There is no need to descend to ./Kbuild in the first place. We can drop the no-clean-files assignment. With this, there is no more user of no-clean-files. I will keep it for a while to see whether a new user will appear. Signed-off-by: Masahiro Yamada