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, 107 insertions, 0 deletions

diff --git a/tools/perf/util/setup.py b/tools/perf/util/setup.py
new file mode 100644
index 000000000..a0ce76624
--- /dev/null
+++ b/tools/perf/util/setup.py
@@ -0,0 +1,107 @@
+from os import getenv, path
+from subprocess import Popen, PIPE
+from re import sub
+import shlex
+
+cc = getenv("CC")
+assert cc, "Environment variable CC not set"
+
+# Check if CC has options, as is the case in yocto, where it uses CC="cc --sysroot..."
+cc_tokens = cc.split()
+if len(cc_tokens) > 1:
+    cc = cc_tokens[0]
+    cc_options = " ".join([str(e) for e in cc_tokens[1:]]) + " "
+else:
+    cc_options = ""
+
+# ignore optional stderr could be None as it is set to PIPE to avoid that.
+# mypy: disable-error-code="union-attr"
+cc_is_clang = b"clang version" in Popen([cc, "-v"], stderr=PIPE).stderr.readline()
+
+srctree = getenv('srctree')
+assert srctree, "Environment variable srctree, for the Linux sources, not set"
+src_feature_tests  = f'{srctree}/tools/build/feature'
+
+def clang_has_option(option):
+    error_substrings = (
+        b"unknown argument",
+        b"is not supported",
+        b"unknown warning option"
+    )
+    cmd = shlex.split(f"{cc} {cc_options} {option}") + [
+        "-o", "/dev/null",
+        path.join(src_feature_tests, "test-hello.c")
+    ]
+    cc_output = Popen(cmd, stderr=PIPE).stderr.readlines()
+    return not any(any(error in line for error in error_substrings) for line in cc_output)
+
+if cc_is_clang:
+    from sysconfig import get_config_vars
+    vars = get_config_vars()
+    for var in ('CFLAGS', 'OPT'):
+        vars[var] = sub("-specs=[^ ]+", "", vars[var])
+        if not clang_has_option("-mcet"):
+            vars[var] = sub("-mcet", "", vars[var])
+        if not clang_has_option("-fcf-protection"):
+            vars[var] = sub("-fcf-protection", "", vars[var])
+        if not clang_has_option("-fstack-clash-protection"):
+            vars[var] = sub("-fstack-clash-protection", "", vars[var])
+        if not clang_has_option("-fstack-protector-strong"):
+            vars[var] = sub("-fstack-protector-strong", "", vars[var])
+        if not clang_has_option("-fno-semantic-interposition"):
+            vars[var] = sub("-fno-semantic-interposition", "", vars[var])
+        if not clang_has_option("-ffat-lto-objects"):
+            vars[var] = sub("-ffat-lto-objects", "", vars[var])
+        if not clang_has_option("-ftree-loop-distribute-patterns"):
+            vars[var] = sub("-ftree-loop-distribute-patterns", "", vars[var])
+        if not clang_has_option("-gno-variable-location-views"):
+            vars[var] = sub("-gno-variable-location-views", "", vars[var])
+
+from setuptools import setup, Extension
+
+from setuptools.command.build_ext   import build_ext   as _build_ext
+from setuptools.command.install_lib import install_lib as _install_lib
+
+class build_ext(_build_ext):
+    def finalize_options(self):
+        _build_ext.finalize_options(self)
+        self.build_lib  = build_lib
+        self.build_temp = build_tmp
+
+class install_lib(_install_lib):
+    def finalize_options(self):
+        _install_lib.finalize_options(self)
+        self.build_dir = build_lib
+
+
+# switch off several checks (need to be at the end of cflags list)
+extra_cflags = ['-fno-strict-aliasing', '-Wno-write-strings', '-Wno-unused-parameter', '-Wno-redundant-decls' ]
+if cc_is_clang:
+    extra_cflags += ["-Wno-unused-command-line-argument" ]
+    if clang_has_option("-Wno-cast-function-type-mismatch"):
+        extra_cflags += ["-Wno-cast-function-type-mismatch" ]
+else:
+    extra_cflags += ['-Wno-cast-function-type' ]
+
+# The python headers have mixed code with declarations (decls after asserts, for instance)
+extra_cflags += [ "-Wno-declaration-after-statement" ]
+
+src_perf  = f'{srctree}/tools/perf'
+build_lib = getenv('PYTHON_EXTBUILD_LIB')
+build_tmp = getenv('PYTHON_EXTBUILD_TMP')
+
+perf = Extension('perf',
+                 sources = [ src_perf + '/util/python.c' ],
+		         include_dirs = ['util/include'],
+		         extra_compile_args = extra_cflags,
+                 )
+
+setup(name='perf',
+      version='0.1',
+      description='Interface with the Linux profiling infrastructure',
+      author='Arnaldo Carvalho de Melo',
+      author_email='acme@redhat.com',
+      license='GPLv2',
+      url='http://perf.wiki.kernel.org',
+      ext_modules=[perf],
+      cmdclass={'build_ext': build_ext, 'install_lib': install_lib})