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linux-yocto/tools/include/uapi
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Thomas Weißschuh 70b9c0c11e uapi: bitops: use UAPI-safe variant of BITS_PER_LONG again (2) 
BITS_PER_LONG does not exist in UAPI headers, so can't be used by the UAPI
__GENMASK(). Instead __BITS_PER_LONG needs to be used.

When __GENMASK() was introduced in commit 3c7a8e190b ("uapi: introduce uapi-friendly macros for GENMASK"),
the code was fine. A broken revert in 1e7933a575 ("uapi: Revert "bitops: avoid integer overflow in GENMASK(_ULL)"")
introduced the incorrect usage of BITS_PER_LONG.
That was fixed in commit 11fcf36850 ("uapi: bitops: use UAPI-safe variant of BITS_PER_LONG again").
But a broken sync of the kernel headers with the tools/ headers in
commit fc92099902 ("tools headers: Synchronize linux/bits.h with the kernel sources")
undid the fix.

Reapply the fix and while at it also fix the tools header.

Fixes: fc92099902 ("tools headers: Synchronize linux/bits.h with the kernel sources")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
2025-07-08 10:23:13 -04:00
..
asm asm-generic: Unify uapi bitsperlong.h for arm64, riscv and loongarch 2023-06-22 17:04:36 +02:00
asm-generic af_unix: Introduce SO_PASSRIGHTS. 2025-05-23 10:24:18 +01:00
drm tools headers UAPI: Sync the drm/drm.h with the kernel sources 2025-06-16 14:05:11 -03:00
linux uapi: bitops: use UAPI-safe variant of BITS_PER_LONG again (2) 2025-07-08 10:23:13 -04:00
README perf tools: Add tools/include/uapi/README 2024-08-06 12:30:08 -07:00

README

Why we want a copy of kernel headers in tools?

There used to be no copies, with tools/ code using kernel headers directly. From time to time tools/perf/ broke due to legitimate kernel hacking. At some point Linus complained about such direct usage. Then we adopted the current model.

The way these headers are used in perf are not restricted to just including them to compile something.

There are sometimes used in scripts that convert defines into string tables, etc, so some change may break one of these scripts, or new MSRs may use some different #define pattern, etc.

E.g.:

$ ls -1 tools/perf/trace/beauty/*.sh | head -5 tools/perf/trace/beauty/arch_errno_names.sh tools/perf/trace/beauty/drm_ioctl.sh tools/perf/trace/beauty/fadvise.sh tools/perf/trace/beauty/fsconfig.sh tools/perf/trace/beauty/fsmount.sh $ $ tools/perf/trace/beauty/fadvise.sh static const char *fadvise_advices[] = { [0] = "NORMAL", [1] = "RANDOM", [2] = "SEQUENTIAL", [3] = "WILLNEED", [4] = "DONTNEED", [5] = "NOREUSE", }; $

The tools/perf/check-headers.sh script, part of the tools/ build process, points out changes in the original files.

So its important not to touch the copies in tools/ when doing changes in the original kernel headers, that will be done later, when check-headers.sh inform about the change to the perf tools hackers.

Another explanation from Ingo Molnar: It's better than all the alternatives we tried so far:

  • Symbolic links and direct #includes: this was the original approach but was pushed back on from the kernel side, when tooling modified the headers and broke them accidentally for kernel builds.

  • Duplicate self-defined ABI headers like glibc: double the maintenance burden, double the chance for mistakes, plus there's no tech-driven notification mechanism to look at new kernel side changes.

What we are doing now is a third option:

  • A software-enforced copy-on-write mechanism of kernel headers to tooling, driven by non-fatal warnings on the tooling side build when kernel headers get modified:

    Warning: Kernel ABI header differences: diff -u tools/include/uapi/drm/i915_drm.h include/uapi/drm/i915_drm.h diff -u tools/include/uapi/linux/fs.h include/uapi/linux/fs.h diff -u tools/include/uapi/linux/kvm.h include/uapi/linux/kvm.h ...

    The tooling policy is to always pick up the kernel side headers as-is, and integate them into the tooling build. The warnings above serve as a notification to tooling maintainers that there's changes on the kernel side.

We've been using this for many years now, and it might seem hacky, but works surprisingly well.