kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 397 insertions, 0 deletions

diff --git a/tools/docs/kernel-doc b/tools/docs/kernel-doc
new file mode 100755
index 000000000..d9192c3f1
--- /dev/null
+++ b/tools/docs/kernel-doc
@@ -0,0 +1,397 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+# Copyright(c) 2025: Mauro Carvalho Chehab <mchehab@kernel.org>.
+#
+# pylint: disable=C0103,R0912,R0914,R0915
+#
+# NOTE: While kernel-doc requires at least version 3.6 to run, the
+#       command line should work with Python 3.2+ (tested with 3.4).
+#       The rationale is that it shall fail gracefully during Kernel
+#       compilation with older Kernel versions. Due to that:
+#       - encoding line is needed here;
+#       - f-strings cannot be used in this file.
+#       - libraries that require newer versions can only be included
+#         after the Python version has been checked.
+#
+# Converted from the kernel-doc script originally written in Perl
+# under GPLv2, copyrighted since 1998 by the following authors:
+#
+#    Aditya Srivastava <yashsri421@gmail.com>
+#    Akira Yokosawa <akiyks@gmail.com>
+#    Alexander A. Klimov <grandmaster@al2klimov.de>
+#    Alexander Lobakin <aleksander.lobakin@intel.com>
+#    André Almeida <andrealmeid@igalia.com>
+#    Andy Shevchenko <andriy.shevchenko@linux.intel.com>
+#    Anna-Maria Behnsen <anna-maria@linutronix.de>
+#    Armin Kuster <akuster@mvista.com>
+#    Bart Van Assche <bart.vanassche@sandisk.com>
+#    Ben Hutchings <ben@decadent.org.uk>
+#    Borislav Petkov <bbpetkov@yahoo.de>
+#    Chen-Yu Tsai <wenst@chromium.org>
+#    Coco Li <lixiaoyan@google.com>
+#    Conchúr Navid <conchur@web.de>
+#    Daniel Santos <daniel.santos@pobox.com>
+#    Danilo Cesar Lemes de Paula <danilo.cesar@collabora.co.uk>
+#    Dan Luedtke <mail@danrl.de>
+#    Donald Hunter <donald.hunter@gmail.com>
+#    Gabriel Krisman Bertazi <krisman@collabora.co.uk>
+#    Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+#    Harvey Harrison <harvey.harrison@gmail.com>
+#    Horia Geanta <horia.geanta@freescale.com>
+#    Ilya Dryomov <idryomov@gmail.com>
+#    Jakub Kicinski <kuba@kernel.org>
+#    Jani Nikula <jani.nikula@intel.com>
+#    Jason Baron <jbaron@redhat.com>
+#    Jason Gunthorpe <jgg@nvidia.com>
+#    Jérémy Bobbio <lunar@debian.org>
+#    Johannes Berg <johannes.berg@intel.com>
+#    Johannes Weiner <hannes@cmpxchg.org>
+#    Jonathan Cameron <Jonathan.Cameron@huawei.com>
+#    Jonathan Corbet <corbet@lwn.net>
+#    Jonathan Neuschäfer <j.neuschaefer@gmx.net>
+#    Kamil Rytarowski <n54@gmx.com>
+#    Kees Cook <kees@kernel.org>
+#    Laurent Pinchart <laurent.pinchart@ideasonboard.com>
+#    Levin, Alexander (Sasha Levin) <alexander.levin@verizon.com>
+#    Linus Torvalds <torvalds@linux-foundation.org>
+#    Lucas De Marchi <lucas.demarchi@profusion.mobi>
+#    Mark Rutland <mark.rutland@arm.com>
+#    Markus Heiser <markus.heiser@darmarit.de>
+#    Martin Waitz <tali@admingilde.org>
+#    Masahiro Yamada <masahiroy@kernel.org>
+#    Matthew Wilcox <willy@infradead.org>
+#    Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
+#    Michal Wajdeczko <michal.wajdeczko@intel.com>
+#    Michael Zucchi
+#    Mike Rapoport <rppt@linux.ibm.com>
+#    Niklas Söderlund <niklas.soderlund@corigine.com>
+#    Nishanth Menon <nm@ti.com>
+#    Paolo Bonzini <pbonzini@redhat.com>
+#    Pavan Kumar Linga <pavan.kumar.linga@intel.com>
+#    Pavel Pisa <pisa@cmp.felk.cvut.cz>
+#    Peter Maydell <peter.maydell@linaro.org>
+#    Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
+#    Randy Dunlap <rdunlap@infradead.org>
+#    Richard Kennedy <richard@rsk.demon.co.uk>
+#    Rich Walker <rw@shadow.org.uk>
+#    Rolf Eike Beer <eike-kernel@sf-tec.de>
+#    Sakari Ailus <sakari.ailus@linux.intel.com>
+#    Silvio Fricke <silvio.fricke@gmail.com>
+#    Simon Huggins
+#    Tim Waugh <twaugh@redhat.com>
+#    Tomasz Warniełło <tomasz.warniello@gmail.com>
+#    Utkarsh Tripathi <utripathi2002@gmail.com>
+#    valdis.kletnieks@vt.edu <valdis.kletnieks@vt.edu>
+#    Vegard Nossum <vegard.nossum@oracle.com>
+#    Will Deacon <will.deacon@arm.com>
+#    Yacine Belkadi <yacine.belkadi.1@gmail.com>
+#    Yujie Liu <yujie.liu@intel.com>
+
+"""
+Print formatted kernel documentation to stdout.
+
+Read C language source or header FILEs, extract embedded
+documentation comments, and print formatted documentation
+to standard output.
+
+The documentation comments are identified by the ``/**``
+opening comment mark.
+
+See Documentation/doc-guide/kernel-doc.rst for the
+documentation comment syntax.
+"""
+
+import argparse
+import logging
+import os
+import sys
+
+# Import Python modules
+
+LIB_DIR = "../lib/python"
+SRC_DIR = os.path.dirname(os.path.realpath(__file__))
+
+sys.path.insert(0, os.path.join(SRC_DIR, LIB_DIR))
+
+WERROR_RETURN_CODE = 3
+
+DESC = """
+Read C language source or header FILEs, extract embedded documentation comments,
+and print formatted documentation to standard output.
+
+The documentation comments are identified by the "/**" opening comment mark.
+
+See Documentation/doc-guide/kernel-doc.rst for the documentation comment syntax.
+"""
+
+EXPORT_FILE_DESC = """
+Specify an additional FILE in which to look for EXPORT_SYMBOL information.
+
+May be used multiple times.
+"""
+
+EXPORT_DESC = """
+Only output documentation for symbols that have been
+exported using EXPORT_SYMBOL() and related macros in any input
+FILE or -export-file FILE.
+"""
+
+INTERNAL_DESC = """
+Only output documentation for symbols that have NOT been
+exported using EXPORT_SYMBOL() and related macros in any input
+FILE or -export-file FILE.
+"""
+
+FUNCTION_DESC = """
+Only output documentation for the given function or DOC: section
+title. All other functions and DOC: sections are ignored.
+
+May be used multiple times.
+"""
+
+NOSYMBOL_DESC = """
+Exclude the specified symbol from the output documentation.
+
+May be used multiple times.
+"""
+
+FILES_DESC = """
+Header and C source files to be parsed.
+"""
+
+WARN_CONTENTS_BEFORE_SECTIONS_DESC = """
+Warn if there are contents before sections (deprecated).
+
+This option is kept just for backward-compatibility, but it does nothing,
+neither here nor at the original Perl script.
+"""
+
+EPILOG = """
+The return value is:
+
+- 0: success or Python version is not compatible with
+kernel-doc.  If -Werror is not used, it will also
+return 0 if there are issues at kernel-doc markups;
+
+- 1: an abnormal condition happened;
+
+- 2: argparse issued an error;
+
+- 3: When -Werror is used, it means that one or more unfiltered parse
+     warnings happened.
+"""
+
+class MsgFormatter(logging.Formatter):
+    """
+    Helper class to capitalize errors and warnings, the same way
+    the venerable (now retired) kernel-doc.pl used to do.
+    """
+
+    def format(self, record):
+        record.levelname = record.levelname.capitalize()
+        return logging.Formatter.format(self, record)
+
+def main():
+    """
+    Main program.
+
+    """
+
+    parser = argparse.ArgumentParser(formatter_class=argparse.RawTextHelpFormatter,
+                                     description=DESC, epilog=EPILOG)
+
+    #
+    # Normal arguments
+    #
+    parser.add_argument("-v", "-verbose", "--verbose", action="store_true",
+                        help="Verbose output, more warnings and other information.")
+
+    parser.add_argument("-d", "-debug", "--debug", action="store_true",
+                        help="Enable debug messages")
+
+    parser.add_argument("-M", "-modulename", "--modulename",
+                        help="Allow setting a module name at the output.")
+
+    parser.add_argument("-l", "-enable-lineno", "--enable_lineno",
+                        action="store_true",
+                        help="Enable line number output (only in ReST mode)")
+
+    #
+    # Arguments to control the warning behavior
+    #
+    parser.add_argument("-Wreturn", "--wreturn", action="store_true",
+                        help="Warns about the lack of a return markup on functions.")
+
+    parser.add_argument("-Wshort-desc", "-Wshort-description", "--wshort-desc",
+                        action="store_true",
+                        help="Warns if initial short description is missing")
+
+    parser.add_argument("-Wcontents-before-sections",
+                        "--wcontents-before-sections", action="store_true",
+                        help=WARN_CONTENTS_BEFORE_SECTIONS_DESC)
+
+    parser.add_argument("-Wall", "--wall", action="store_true",
+                        help="Enable all types of warnings")
+
+    parser.add_argument("-Werror", "--werror", action="store_true",
+                        help="Treat warnings as errors.")
+
+    parser.add_argument("-export-file", "--export-file", action='append',
+                        help=EXPORT_FILE_DESC)
+
+    #
+    # Output format
+    #
+    out_fmt = parser.add_argument_group("Output format selection (mutually exclusive)")
+
+    out_fmt.add_argument("-m", "-man", "--man", action="store_true",
+                         help="Output troff manual page format.")
+    out_fmt.add_argument("-r", "-rst", "--rst", action="store_true",
+                         help="Output reStructuredText format (default).")
+    out_fmt.add_argument("-N", "-none", "--none", action="store_true",
+                         help="Do not output documentation, only warnings.")
+
+    out_fmt.add_argument("-y", "--yaml-file", "--yaml",
+                         help="Stores kernel-doc output on a yaml file.")
+    out_fmt.add_argument("-k", "--kdoc-item", "--kdoc", action="store_true",
+                         help="Store KdocItem inside yaml file. Ued together with --yaml.")
+
+
+    #
+    # Output selection mutually-exclusive group
+    #
+    sel_group = parser.add_argument_group("Output selection (mutually exclusive)")
+    sel_mut = sel_group.add_mutually_exclusive_group()
+
+    sel_mut.add_argument("-e", "-export", "--export", action='store_true',
+                         help=EXPORT_DESC)
+
+    sel_mut.add_argument("-i", "-internal", "--internal", action='store_true',
+                         help=INTERNAL_DESC)
+
+    sel_mut.add_argument("-s", "-function", "--symbol", action='append',
+                         help=FUNCTION_DESC)
+
+    #
+    # Those are valid for all 3 types of filter
+    #
+    parser.add_argument("-n", "-nosymbol", "--nosymbol", action='append',
+                        help=NOSYMBOL_DESC)
+
+    parser.add_argument("-D", "-no-doc-sections", "--no-doc-sections",
+                        action='store_true', help="Don't output DOC sections")
+
+    parser.add_argument("files", metavar="FILE",
+                        nargs="+", help=FILES_DESC)
+
+    args = parser.parse_args()
+
+    if args.wall:
+        args.wreturn = True
+        args.wshort_desc = True
+        args.wcontents_before_sections = True
+
+    logger = logging.getLogger()
+
+    if not args.debug:
+        logger.setLevel(logging.INFO)
+    else:
+        logger.setLevel(logging.DEBUG)
+
+    formatter = MsgFormatter('%(levelname)s: %(message)s')
+
+    handler = logging.StreamHandler()
+    handler.setFormatter(formatter)
+
+    logger.addHandler(handler)
+
+    python_ver = sys.version_info[:2]
+    if python_ver < (3,6):
+        #
+        # Depending on the Kernel configuration, kernel-doc --none is called at
+        # build time. As we don't want to break compilation due to the
+        # usage of an old Python version, return 0 here.
+        #
+        if args.none:
+            logger.error("Python 3.6 or later is required by kernel-doc. Skipping checks")
+            sys.exit(0)
+
+        sys.exit("Python 3.6 or later is required by kernel-doc. Aborting.")
+
+    if python_ver < (3,7):
+        logger.warning("Python 3.7 or later is required for correct results")
+
+    #
+    # Import kernel-doc libraries only after checking the Python version
+    #
+    from kdoc.kdoc_files import KernelFiles             # pylint: disable=C0415
+    from kdoc.kdoc_output import RestFormat, ManFormat  # pylint: disable=C0415
+
+    yaml_content = set()
+    if args.yaml_file:
+        out_style = None
+
+        if args.man:
+            yaml_content |= {"man"}
+
+        if args.rst:
+            yaml_content |= {"rst"}
+
+        if args.kdoc_item or not yaml_content:
+            yaml_content |= {"KdocItem"}
+
+    else:
+        n_outputs = 0
+
+        if args.man:
+            out_style = ManFormat(modulename=args.modulename)
+            n_outputs += 1
+
+        if args.none:
+            out_style = None
+            n_outputs += 1
+
+        if  args.rst or n_outputs == 0:
+            n_outputs += 1
+            out_style = RestFormat()
+
+        if n_outputs > 1:
+             parser.error("Those arguments are muttually exclusive: --man, --rst, --none, except when generating a YAML file.")
+
+        elif not n_outputs:
+            out_style = RestFormat()
+
+    kfiles = KernelFiles(verbose=args.verbose,
+                         yaml_file=args.yaml_file, yaml_content=yaml_content,
+                         out_style=out_style, werror=args.werror,
+                         wreturn=args.wreturn, wshort_desc=args.wshort_desc,
+                         wcontents_before_sections=args.wcontents_before_sections)
+
+    kfiles.parse(args.files, export_file=args.export_file)
+
+    for t in kfiles.msg(enable_lineno=args.enable_lineno, export=args.export,
+                        internal=args.internal, symbol=args.symbol,
+                        nosymbol=args.nosymbol, export_file=args.export_file,
+                        no_doc_sections=args.no_doc_sections):
+        msg = t[1]
+        if msg:
+            print(msg)
+
+    error_count = kfiles.errors
+    if not error_count:
+        sys.exit(0)
+
+    if args.werror:
+        print("%s warnings as errors" % error_count)    # pylint: disable=C0209
+        sys.exit(WERROR_RETURN_CODE)
+
+    if args.verbose:
+        print("%s errors" % error_count)                # pylint: disable=C0209
+
+    sys.exit(0)
+
+#
+# Call main method
+#
+if __name__ == "__main__":
+    main()