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, 275 insertions, 0 deletions

diff --git a/Documentation/sphinx/kerneldoc.py b/Documentation/sphinx/kerneldoc.py
new file mode 100644
index 000000000..c1cadb4eb
--- /dev/null
+++ b/Documentation/sphinx/kerneldoc.py
@@ -0,0 +1,275 @@
+# coding=utf-8
+# SPDX-License-Identifier: MIT
+#
+# Copyright © 2016 Intel Corporation
+#
+# Permission is hereby granted, free of charge, to any person obtaining a
+# copy of this software and associated documentation files (the "Software"),
+# to deal in the Software without restriction, including without limitation
+# the rights to use, copy, modify, merge, publish, distribute, sublicense,
+# and/or sell copies of the Software, and to permit persons to whom the
+# Software is furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice (including the next
+# paragraph) shall be included in all copies or substantial portions of the
+# Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+# THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+# IN THE SOFTWARE.
+#
+# Authors:
+#    Jani Nikula <jani.nikula@intel.com>
+#
+
+import codecs
+import os
+import subprocess
+import sys
+import re
+import glob
+
+from docutils import nodes, statemachine
+from docutils.statemachine import ViewList
+from docutils.parsers.rst import directives, Directive
+import sphinx
+from sphinx.util.docutils import switch_source_input
+from sphinx.util import logging
+from pprint import pformat
+
+srctree = os.path.abspath(os.environ["srctree"])
+sys.path.insert(0, os.path.join(srctree, "tools/lib/python"))
+
+from kdoc.kdoc_files import KernelFiles
+from kdoc.kdoc_output import RestFormat
+
+# Used when verbose is active to show how to reproduce kernel-doc
+# issues via command line
+kerneldoc_bin = "tools/docs/kernel-doc"
+
+__version__  = '1.0'
+kfiles = None
+logger = logging.getLogger(__name__)
+
+def cmd_str(cmd):
+    """
+    Helper function to output a command line that can be used to produce
+    the same records via command line. Helpful to debug troubles at the
+    script.
+    """
+
+    cmd_line = ""
+
+    for w in cmd:
+        if w == "" or " " in w:
+            esc_cmd = "'" + w + "'"
+        else:
+            esc_cmd = w
+
+        if cmd_line:
+            cmd_line += " " + esc_cmd
+            continue
+        else:
+            cmd_line = esc_cmd
+
+    return cmd_line
+
+class KernelDocDirective(Directive):
+    """Extract kernel-doc comments from the specified file"""
+    required_argument = 1
+    optional_arguments = 4
+    option_spec = {
+        'doc': directives.unchanged_required,
+        'export': directives.unchanged,
+        'internal': directives.unchanged,
+        'identifiers': directives.unchanged,
+        'no-identifiers': directives.unchanged,
+        'functions': directives.unchanged,
+    }
+    has_content = False
+    verbose = 0
+
+    parse_args = {}
+    msg_args = {}
+
+    def handle_args(self):
+
+        env = self.state.document.settings.env
+        cmd = [kerneldoc_bin, '-rst', '-enable-lineno']
+
+        filename = env.config.kerneldoc_srctree + '/' + self.arguments[0]
+
+        # Arguments used by KernelFiles.parse() function
+        self.parse_args = {
+            "file_list": [filename],
+            "export_file": []
+        }
+
+        # Arguments used by KernelFiles.msg() function
+        self.msg_args = {
+            "enable_lineno": True,
+            "export": False,
+            "internal": False,
+            "symbol": [],
+            "nosymbol": [],
+            "no_doc_sections": False
+        }
+
+        export_file_patterns = []
+
+        verbose = os.environ.get("V")
+        if verbose:
+            try:
+                self.verbose = int(verbose)
+            except ValueError:
+                pass
+
+        # Tell sphinx of the dependency
+        env.note_dependency(os.path.abspath(filename))
+
+        self.tab_width = self.options.get('tab-width',
+                                          self.state.document.settings.tab_width)
+
+        # 'function' is an alias of 'identifiers'
+        if 'functions' in self.options:
+            self.options['identifiers'] = self.options.get('functions')
+
+        # FIXME: make this nicer and more robust against errors
+        if 'export' in self.options:
+            cmd += ['-export']
+            self.msg_args["export"] = True
+            export_file_patterns = str(self.options.get('export')).split()
+        elif 'internal' in self.options:
+            cmd += ['-internal']
+            self.msg_args["internal"] = True
+            export_file_patterns = str(self.options.get('internal')).split()
+        elif 'doc' in self.options:
+            func = str(self.options.get('doc'))
+            cmd += ['-function', func]
+            self.msg_args["symbol"].append(func)
+        elif 'identifiers' in self.options:
+            identifiers = self.options.get('identifiers').split()
+            if identifiers:
+                for i in identifiers:
+                    i = i.rstrip("\\").strip()
+                    if not i:
+                        continue
+
+                    cmd += ['-function', i]
+                    self.msg_args["symbol"].append(i)
+            else:
+                cmd += ['-no-doc-sections']
+                self.msg_args["no_doc_sections"] = True
+
+        if 'no-identifiers' in self.options:
+            no_identifiers = self.options.get('no-identifiers').split()
+            if no_identifiers:
+                for i in no_identifiers:
+                    i = i.rstrip("\\").strip()
+                    if not i:
+                        continue
+
+                    cmd += ['-nosymbol', i]
+                    self.msg_args["nosymbol"].append(i)
+
+        for pattern in export_file_patterns:
+            pattern = pattern.rstrip("\\").strip()
+            if not pattern:
+                continue
+
+            for f in glob.glob(env.config.kerneldoc_srctree + '/' + pattern):
+                env.note_dependency(os.path.abspath(f))
+                cmd += ['-export-file', f]
+                self.parse_args["export_file"].append(f)
+
+            # Export file is needed by both parse and msg, as kernel-doc
+            # cache exports.
+            self.msg_args["export_file"] = self.parse_args["export_file"]
+
+        cmd += [filename]
+
+        return cmd
+
+    def parse_msg(self, filename, node, out):
+        """
+        Handles a kernel-doc output for a given file
+        """
+
+        env = self.state.document.settings.env
+
+        lines = statemachine.string2lines(out, self.tab_width,
+                                            convert_whitespace=True)
+        result = ViewList()
+
+        lineoffset = 0;
+        line_regex = re.compile(r"^\.\. LINENO ([0-9]+)$")
+        for line in lines:
+            match = line_regex.search(line)
+            if match:
+                # sphinx counts lines from 0
+                lineoffset = int(match.group(1)) - 1
+                # we must eat our comments since the upset the markup
+            else:
+                doc = str(env.srcdir) + "/" + env.docname + ":" + str(self.lineno)
+                result.append(line, doc + ": " + filename, lineoffset)
+                lineoffset += 1
+
+        self.do_parse(result, node)
+
+    def run_kdoc(self, kfiles):
+        """
+        Execute kernel-doc classes directly instead of running as a separate
+        command.
+        """
+
+        env = self.state.document.settings.env
+
+        node = nodes.section()
+
+        kfiles.parse(**self.parse_args)
+        filenames = self.parse_args["file_list"]
+
+        for filename, out in kfiles.msg(**self.msg_args, filenames=filenames):
+            self.parse_msg(filename, node, out)
+
+        return node.children
+
+    def run(self):
+        cmd = self.handle_args()
+        if self.verbose >= 1:
+            logger.info(cmd_str(cmd))
+
+        try:
+            return self.run_kdoc(kfiles)
+        except Exception as e:  # pylint: disable=W0703
+            logger.warning("kernel-doc '%s' processing failed with: %s" %
+                           (cmd_str(cmd), pformat(e)))
+            return [nodes.error(None, nodes.paragraph(text = "kernel-doc missing"))]
+
+    def do_parse(self, result, node):
+        with switch_source_input(self.state, result):
+            self.state.nested_parse(result, 0, node, match_titles=1)
+
+def setup_kfiles(app):
+    global kfiles
+    out_style = RestFormat()
+    kfiles = KernelFiles(out_style=out_style, logger=logger)
+
+
+def setup(app):
+    app.add_config_value('kerneldoc_srctree', None, 'env')
+    app.add_config_value('kerneldoc_verbosity', 1, 'env')
+
+    app.add_directive('kernel-doc', KernelDocDirective)
+
+    app.connect('builder-inited', setup_kfiles)
+
+    return dict(
+        version = __version__,
+        parallel_read_safe = True,
+        parallel_write_safe = True
+    )