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, 98 insertions, 0 deletions

diff --git a/tools/perf/util/target.h b/tools/perf/util/target.h
new file mode 100644
index 000000000..bc2bff9c6
--- /dev/null
+++ b/tools/perf/util/target.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _PERF_TARGET_H
+#define _PERF_TARGET_H
+
+#include <stdbool.h>
+#include <sys/types.h>
+
+struct target {
+	const char   *pid;
+	const char   *tid;
+	const char   *cpu_list;
+	const char   *bpf_str;
+	bool	     system_wide;
+	bool	     uses_mmap;
+	bool	     default_per_cpu;
+	bool	     per_thread;
+	bool	     use_bpf;
+	bool	     inherit;
+	int	     initial_delay;
+	const char   *attr_map;
+};
+
+enum target_errno {
+	TARGET_ERRNO__SUCCESS		= 0,
+
+	/*
+	 * Choose an arbitrary negative big number not to clash with standard
+	 * errno since SUS requires the errno has distinct positive values.
+	 * See 'Issue 6' in the link below.
+	 *
+	 * http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/errno.h.html
+	 */
+	__TARGET_ERRNO__START		= -10000,
+
+	/* for target__validate() */
+	TARGET_ERRNO__PID_OVERRIDE_CPU	= __TARGET_ERRNO__START,
+	TARGET_ERRNO__PID_OVERRIDE_SYSTEM,
+	TARGET_ERRNO__SYSTEM_OVERRIDE_THREAD,
+	TARGET_ERRNO__BPF_OVERRIDE_CPU,
+	TARGET_ERRNO__BPF_OVERRIDE_PID,
+	TARGET_ERRNO__BPF_OVERRIDE_THREAD,
+
+	__TARGET_ERRNO__END,
+};
+
+enum target_errno target__validate(struct target *target);
+
+uid_t parse_uid(const char *str);
+
+int target__strerror(struct target *target, int errnum, char *buf, size_t buflen);
+
+static inline bool target__has_task(const struct target *target)
+{
+	return target->tid || target->pid;
+}
+
+static inline bool target__has_cpu(const struct target *target)
+{
+	return target->system_wide || target->cpu_list;
+}
+
+static inline bool target__none(const struct target *target)
+{
+	return !target__has_task(target) && !target__has_cpu(target);
+}
+
+static inline bool target__enable_on_exec(const struct target *target)
+{
+	/*
+	 * Normally enable_on_exec should be set if:
+	 *  1) The tracee process is forked (not attaching to existed task or cpu).
+	 *  2) And initial_delay is not configured.
+	 * Otherwise, we enable tracee events manually.
+	 */
+	return target__none(target) && !target->initial_delay;
+}
+
+static inline bool target__has_per_thread(const struct target *target)
+{
+	return target->system_wide && target->per_thread;
+}
+
+static inline bool target__uses_dummy_map(const struct target *target)
+{
+	bool use_dummy = false;
+
+	if (target->default_per_cpu)
+		use_dummy = target->per_thread ? true : false;
+	else if (target__has_task(target) ||
+	         (!target__has_cpu(target) && !target->uses_mmap))
+		use_dummy = true;
+	else if (target__has_per_thread(target))
+		use_dummy = true;
+
+	return use_dummy;
+}
+
+#endif /* _PERF_TARGET_H */