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, 142 insertions, 0 deletions

diff --git a/tools/perf/util/data.h b/tools/perf/util/data.h
new file mode 100644
index 000000000..8299fb5fa
--- /dev/null
+++ b/tools/perf/util/data.h
@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_DATA_H
+#define __PERF_DATA_H
+
+#include <stdio.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <linux/types.h>
+
+enum perf_data_mode {
+	PERF_DATA_MODE_WRITE,
+	PERF_DATA_MODE_READ,
+};
+
+enum perf_dir_version {
+	PERF_DIR_SINGLE_FILE	= 0,
+	PERF_DIR_VERSION	= 1,
+};
+
+/**
+ * struct perf_data_file: A wrapper around a file used for perf.data reading or writing. Generally
+ * part of struct perf_data.
+ */
+struct perf_data_file {
+	/**
+	 * @path: Path of file. Generally a copy of perf_data.path but for a
+	 * directory it is the file within the directory.
+	 */
+	char		*path;
+	union {
+		/** @fd: File descriptor for read/writes. Valid if use_stdio is false. */
+		int	 fd;
+		/**
+		 * @fptr: Stdio FILE. Valid if use_stdio is true, currently just
+		 * pipes in perf inject.
+		 */
+		FILE	*fptr;
+	};
+	/** @size: Size of file when opened. */
+	unsigned long	 size;
+	/** @use_stdio: Use buffered stdio operations. */
+	bool		 use_stdio;
+};
+
+/**
+ * struct perf_data: A wrapper around a file used for perf.data reading or writing.
+ */
+struct perf_data {
+	/** @path: Path to open and of the file. NULL implies 'perf.data' will be used. */
+	const char		*path;
+	/** @file: Underlying file to be used. */
+	struct perf_data_file	 file;
+	/** @is_pipe: Underlying file is a pipe. */
+	bool			 is_pipe;
+	/** @is_dir: Underlying file is a directory. */
+	bool			 is_dir;
+	/** @force: Ignore opening a file creating created by a different user. */
+	bool			 force;
+	/** @in_place_update: A file opened for reading but will be written to. */
+	bool			 in_place_update;
+	/** @mode: Read or write mode. */
+	enum perf_data_mode	 mode;
+
+	struct {
+		/** @version: perf_dir_version. */
+		u64			 version;
+		/** @files: perf data files for the directory. */
+		struct perf_data_file	*files;
+		/** @nr: Number of perf data files for the directory. */
+		int			 nr;
+	} dir;
+};
+
+static inline int perf_data_file__fd(struct perf_data_file *file)
+{
+	return file->use_stdio ? fileno(file->fptr) : file->fd;
+}
+
+ssize_t perf_data_file__write(struct perf_data_file *file,
+			      void *buf, size_t size);
+off_t perf_data_file__seek(struct perf_data_file *file, off_t offset, int whence);
+
+
+static inline bool perf_data__is_read(struct perf_data *data)
+{
+	return data->mode == PERF_DATA_MODE_READ;
+}
+
+static inline bool perf_data__is_write(struct perf_data *data)
+{
+	return data->mode == PERF_DATA_MODE_WRITE;
+}
+
+static inline int perf_data__is_pipe(struct perf_data *data)
+{
+	return data->is_pipe;
+}
+
+static inline bool perf_data__is_dir(struct perf_data *data)
+{
+	return data->is_dir;
+}
+
+static inline bool perf_data__is_single_file(struct perf_data *data)
+{
+	return data->dir.version == PERF_DIR_SINGLE_FILE;
+}
+
+static inline int perf_data__fd(struct perf_data *data)
+{
+	return perf_data_file__fd(&data->file);
+}
+
+int perf_data__open(struct perf_data *data);
+void perf_data__close(struct perf_data *data);
+ssize_t perf_data__read(struct perf_data *data, void *buf, size_t size);
+ssize_t perf_data__write(struct perf_data *data,
+			 void *buf, size_t size);
+off_t perf_data__seek(struct perf_data *data, off_t offset, int whence);
+/*
+ * If at_exit is set, only rename current perf.data to
+ * perf.data.<postfix>, continue write on original data.
+ * Set at_exit when flushing the last output.
+ *
+ * Return value is fd of new output.
+ */
+int perf_data__switch(struct perf_data *data,
+		      const char *postfix,
+		      size_t pos, bool at_exit, char **new_filepath);
+
+int perf_data__create_dir(struct perf_data *data, int nr);
+int perf_data__open_dir(struct perf_data *data);
+void perf_data__close_dir(struct perf_data *data);
+unsigned long perf_data__size(struct perf_data *data);
+int perf_data__make_kcore_dir(struct perf_data *data, char *buf, size_t buf_sz);
+char *perf_data__kallsyms_name(struct perf_data *data);
+char *perf_data__guest_kallsyms_name(struct perf_data *data, pid_t machine_pid);
+
+bool has_kcore_dir(const char *path);
+bool is_perf_data(const char *path);
+
+#endif /* __PERF_DATA_H */