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, 234 insertions, 0 deletions

diff --git a/tools/perf/util/kvm-stat.h b/tools/perf/util/kvm-stat.h
new file mode 100644
index 000000000..cdbd921a5
--- /dev/null
+++ b/tools/perf/util/kvm-stat.h
@@ -0,0 +1,234 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_KVM_STAT_H
+#define __PERF_KVM_STAT_H
+
+#include "tool.h"
+#include "sort.h"
+#include "stat.h"
+#include "symbol.h"
+#include "record.h"
+
+#include <errno.h>
+#include <stdlib.h>
+#include <linux/zalloc.h>
+
+#define KVM_EVENT_NAME_LEN	40
+
+struct evsel;
+struct evlist;
+struct perf_session;
+
+struct event_key {
+	#define INVALID_KEY     (~0ULL)
+	u64 key;
+	int info;
+	struct exit_reasons_table *exit_reasons;
+};
+
+struct kvm_info {
+	char name[KVM_EVENT_NAME_LEN];
+	refcount_t refcnt;
+};
+
+struct kvm_event_stats {
+	u64 time;
+	struct stats stats;
+};
+
+struct perf_kvm_stat;
+
+struct kvm_event {
+	struct list_head hash_entry;
+
+	struct perf_kvm_stat *perf_kvm;
+	struct event_key key;
+
+	struct kvm_event_stats total;
+
+	#define DEFAULT_VCPU_NUM 8
+	int max_vcpu;
+	struct kvm_event_stats *vcpu;
+
+	struct hist_entry he;
+};
+
+struct child_event_ops {
+	void (*get_key)(struct perf_sample *sample,
+			struct event_key *key);
+	const char *name;
+};
+
+struct kvm_events_ops {
+	bool (*is_begin_event)(struct perf_sample *sample,
+			       struct event_key *key);
+	bool (*is_end_event)(struct perf_sample *sample, struct event_key *key);
+	const struct child_event_ops *child_ops;
+	void (*decode_key)(struct perf_kvm_stat *kvm, struct event_key *key,
+			   char *decode);
+	const char *name;
+};
+
+struct exit_reasons_table {
+	unsigned long exit_code;
+	const char *reason;
+};
+
+struct perf_kvm_stat {
+	struct perf_tool    tool;
+	struct record_opts  opts;
+	struct evlist  *evlist;
+	struct perf_session *session;
+
+	const char *file_name;
+	const char *report_event;
+	const char *sort_key;
+	int trace_vcpu;
+
+	/* Used when process events */
+	struct addr_location al;
+
+	struct exit_reasons_table *exit_reasons;
+	const char *exit_reasons_isa;
+
+	const struct kvm_events_ops *events_ops;
+
+	u64 total_time;
+	u64 total_count;
+	u64 lost_events;
+	u64 duration;
+
+	struct intlist *pid_list;
+
+	int timerfd;
+	unsigned int display_time;
+	bool live;
+	bool force;
+	bool use_stdio;
+};
+
+struct kvm_reg_events_ops {
+	const char *name;
+	const struct kvm_events_ops *ops;
+};
+
+#ifdef HAVE_LIBTRACEEVENT
+
+void exit_event_get_key(struct perf_sample *sample,
+			struct event_key *key);
+bool exit_event_begin(struct perf_sample *sample,
+		      struct event_key *key);
+bool exit_event_end(struct perf_sample *sample,
+		    struct event_key *key);
+void exit_event_decode_key(struct perf_kvm_stat *kvm,
+			   struct event_key *key,
+			   char *decode);
+
+bool kvm_exit_event(struct evsel *evsel);
+bool kvm_entry_event(struct evsel *evsel);
+
+#define define_exit_reasons_table(name, symbols)	\
+	static struct exit_reasons_table name[] = {	\
+		symbols, { -1, NULL }			\
+	}
+
+/*
+ * arch specific callbacks and data structures
+ */
+int setup_kvm_events_tp(struct perf_kvm_stat *kvm, uint16_t e_machine);
+int __setup_kvm_events_tp_powerpc(struct perf_kvm_stat *kvm);
+
+int cpu_isa_init(struct perf_kvm_stat *kvm, uint16_t e_machine, const char *cpuid);
+int __cpu_isa_init_arm64(struct perf_kvm_stat *kvm);
+int __cpu_isa_init_loongarch(struct perf_kvm_stat *kvm);
+int __cpu_isa_init_powerpc(struct perf_kvm_stat *kvm);
+int __cpu_isa_init_riscv(struct perf_kvm_stat *kvm);
+int __cpu_isa_init_s390(struct perf_kvm_stat *kvm, const char *cpuid);
+int __cpu_isa_init_x86(struct perf_kvm_stat *kvm, const char *cpuid);
+
+const char *vcpu_id_str(uint16_t e_machine);
+const char *kvm_exit_reason(uint16_t e_machine);
+const char *kvm_entry_trace(uint16_t e_machine);
+const char *kvm_exit_trace(uint16_t e_machine);
+
+const char * const *kvm_events_tp(uint16_t e_machine);
+const char * const *__kvm_events_tp_arm64(void);
+const char * const *__kvm_events_tp_loongarch(void);
+const char * const *__kvm_events_tp_powerpc(void);
+const char * const *__kvm_events_tp_riscv(void);
+const char * const *__kvm_events_tp_s390(void);
+const char * const *__kvm_events_tp_x86(void);
+
+const struct kvm_reg_events_ops *kvm_reg_events_ops(uint16_t e_machine);
+const struct kvm_reg_events_ops *__kvm_reg_events_ops_arm64(void);
+const struct kvm_reg_events_ops *__kvm_reg_events_ops_loongarch(void);
+const struct kvm_reg_events_ops *__kvm_reg_events_ops_powerpc(void);
+const struct kvm_reg_events_ops *__kvm_reg_events_ops_riscv(void);
+const struct kvm_reg_events_ops *__kvm_reg_events_ops_s390(void);
+const struct kvm_reg_events_ops *__kvm_reg_events_ops_x86(void);
+
+const char * const *kvm_skip_events(uint16_t e_machine);
+const char * const *__kvm_skip_events_arm64(void);
+const char * const *__kvm_skip_events_loongarch(void);
+const char * const *__kvm_skip_events_powerpc(void);
+const char * const *__kvm_skip_events_riscv(void);
+const char * const *__kvm_skip_events_s390(void);
+const char * const *__kvm_skip_events_x86(void);
+
+int kvm_add_default_arch_event(uint16_t e_machine, int *argc, const char **argv);
+int __kvm_add_default_arch_event_powerpc(int *argc, const char **argv);
+int __kvm_add_default_arch_event_x86(int *argc, const char **argv);
+
+#else /* !HAVE_LIBTRACEEVENT */
+
+static inline int kvm_add_default_arch_event(uint16_t e_machine __maybe_unused,
+					     int *argc __maybe_unused,
+					     const char **argv __maybe_unused)
+{
+	return 0;
+}
+
+#endif /* HAVE_LIBTRACEEVENT */
+
+static inline struct kvm_info *kvm_info__get(struct kvm_info *ki)
+{
+	if (ki)
+		refcount_inc(&ki->refcnt);
+	return ki;
+}
+
+static inline void kvm_info__put(struct kvm_info *ki)
+{
+	if (ki && refcount_dec_and_test(&ki->refcnt))
+		free(ki);
+}
+
+static inline void __kvm_info__zput(struct kvm_info **ki)
+{
+	kvm_info__put(*ki);
+	*ki = NULL;
+}
+
+#define kvm_info__zput(ki) __kvm_info__zput(&ki)
+
+static inline struct kvm_info *kvm_info__new(void)
+{
+	struct kvm_info *ki;
+
+	ki = zalloc(sizeof(*ki));
+	if (ki)
+		refcount_set(&ki->refcnt, 1);
+
+	return ki;
+}
+
+#define STRDUP_FAIL_EXIT(s)		\
+	({	char *_p;		\
+		_p = strdup(s);		\
+		if (!_p) {		\
+			ret = -ENOMEM;	\
+			goto EXIT;	\
+		}			\
+		_p;			\
+	})
+
+#endif /* __PERF_KVM_STAT_H */