mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-02-15 05:03:01 -05:00
ddc592972f
To pick up the changes in:af5366bea2KVM: x86: Drop the now unused KVM_X86_DISABLE_VALID_EXITS915d2f0718KVM: Move KVM_REG_SIZE() definition to common uAPI header5c17848134KVM: x86/xen: Restrict hypercall MSR to unofficial synthetic range9364789567KVM: x86: Add a VM type define for TDXfa662c9080KVM: SVM: Add Idle HLT intercept support3adaee7830KVM: arm64: Allow userspace to change the implementation ID registersfaf7714a47KVM: arm64: nv: Allow userland to set VGIC maintenance IRQc0000e58c7KVM: arm64: Introduce KVM_REG_ARM_VENDOR_HYP_BMAP_2f83c41fb3dKVM: arm64: Allow userspace to limit NV support to nVHE Addressing this perf tools build warning: Warning: Kernel ABI header differences: diff -u tools/include/uapi/linux/kvm.h include/uapi/linux/kvm.h diff -u tools/arch/x86/include/uapi/asm/kvm.h arch/x86/include/uapi/asm/kvm.h diff -u tools/arch/x86/include/uapi/asm/svm.h arch/x86/include/uapi/asm/svm.h diff -u tools/arch/arm64/include/uapi/asm/kvm.h arch/arm64/include/uapi/asm/kvm.h Please see tools/include/uapi/README for further details. Acked-by: Ingo Molnar <mingo@kernel.org> Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com> Cc: kvm@vger.kernel.org Link: https://lore.kernel.org/r/20250410001125.391820-2-namhyung@kernel.org Signed-off-by: Namhyung Kim <namhyung@kernel.org>
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.