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Linus Torvalds 78bb43e51b Updates for the generic entry code: - Split the code into syscall and exception/interrupt parts to ease the conversion of ARM[64] to the generic entry infrastructure - Extend syscall user dispatching to support a single intercepted range instead of the default single non-intercepted range. That allows monitoring/analysis of a specific executable range, e.g. a library, and also provides flexibility for sandboxing scenarios. - Cleanup and extend the user dispatch selftest -----BEGIN PGP SIGNATURE----- iQJHBAABCgAxFiEEQp8+kY+LLUocC4bMphj1TA10mKEFAmiIg6UTHHRnbHhAbGlu dXRyb25peC5kZQAKCRCmGPVMDXSYoWn7EACTvQpu7tGd1rN9hCjiB1W5po7nvlCd gKghjS9Kp0KttTDQPLVcmnH06BhDHWNNn1HXZ1ORea4bpLywiKHtVgqUAsJDsBsv ETeTHYNphk0sktvAqp3XusA6HF4T0s1KXJQj3W1ACrYZWRkK/VystCLYwBRGpc3r cj7jAFmJyNpU236R5XYJ7ooHfPYpzZ8VAHBO8ykK7muHDfyBRXEIlmkGep++ctSv v0uZXAy6LONljKg87YJTien0UA7ze9lFgPTuV1y/qfaLbYNekUaJSDjfuhOpZZUw TzSh9OYoIvKpd0ylHwB1qMLd5CaXNicaeLfTW3xbX06KaXa7WNAonS35sK0EjhtZ 0bBA9g6bRhphyh0tzR4saF9bczNvJydNCn7/QFo9dKbQUEL/FRXtJiIeusVx/0fJ +ZqWRTcEdDw2Rsyv52hKgyEJi7F3nL9ovabUN9P1/0aPcTdM3WekMpSOJm1U6wVF e6oSyeoeNdjcdxgWbQrgRNbmq5CPEV3ig5J+G418r5DTF3ifqZX+WscijUtKTu5K V5GpLc0PL9eoigQ37LmGkwK/4xoB9SAPTQuzUs9qgh9NidwT0cCfoNxpeGh6GeHX GLHPGU61vZaefxpwuAuv+SQSgxXSKk2/H/ijPzSjrX/PkUp7MoX9XoOQAh4FxZjO ok5YEUGXzSJfXQ== =yaCQ -----END PGP SIGNATURE----- Merge tag 'core-entry-2025-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull generic entry code updates from Thomas Gleixner: - Split the code into syscall and exception/interrupt parts to ease the conversion of ARM[64] to the generic entry infrastructure - Extend syscall user dispatching to support a single intercepted range instead of the default single non-intercepted range. That allows monitoring/analysis of a specific executable range, e.g. a library, and also provides flexibility for sandboxing scenarios - Cleanup and extend the user dispatch selftest * tag 'core-entry-2025-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: entry: Split generic entry into generic exception and syscall entry selftests: Add tests for PR_SYS_DISPATCH_INCLUSIVE_ON syscall_user_dispatch: Add PR_SYS_DISPATCH_INCLUSIVE_ON selftests: Fix errno checking in syscall_user_dispatch test		2025-07-29 15:14:29 -07:00
..
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	Updates for the generic entry code:	2025-07-29 15:14:29 -07:00
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.