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, 380 insertions, 0 deletions

diff --git a/tools/perf/util/debug.c b/tools/perf/util/debug.c
new file mode 100644
index 000000000..6b5ffe81f
--- /dev/null
+++ b/tools/perf/util/debug.c
@@ -0,0 +1,380 @@
+// SPDX-License-Identifier: GPL-2.0
+/* For general debugging purposes */
+
+#include <inttypes.h>
+#include <string.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+#include <api/debug.h>
+#include <linux/kernel.h>
+#include <linux/time64.h>
+#include <sys/time.h>
+#ifdef HAVE_BACKTRACE_SUPPORT
+#include <execinfo.h>
+#endif
+#include "addr_location.h"
+#include "color.h"
+#include "debug.h"
+#include "env.h"
+#include "event.h"
+#include "machine.h"
+#include "map.h"
+#include "print_binary.h"
+#include "srcline.h"
+#include "symbol.h"
+#include "synthetic-events.h"
+#include "target.h"
+#include "thread.h"
+#include "trace-event.h"
+#include "ui/helpline.h"
+#include "ui/ui.h"
+#include "util/parse-sublevel-options.h"
+
+#include <linux/ctype.h>
+
+#ifdef HAVE_LIBTRACEEVENT
+#include <event-parse.h>
+#else
+#define LIBTRACEEVENT_VERSION 0
+#endif
+
+int verbose;
+int debug_kmaps;
+int debug_peo_args;
+bool dump_trace = false, quiet = false;
+int debug_ordered_events;
+static int redirect_to_stderr;
+int debug_data_convert;
+static FILE *_debug_file;
+static bool debug_display_time;
+int debug_type_profile;
+
+FILE *debug_file(void)
+{
+	if (!_debug_file) {
+		debug_set_file(stderr);
+		pr_warning_once("debug_file not set");
+	}
+	return _debug_file;
+}
+
+void debug_set_file(FILE *file)
+{
+	_debug_file = file;
+}
+
+void debug_set_display_time(bool set)
+{
+	debug_display_time = set;
+}
+
+static int fprintf_time(FILE *file)
+{
+	struct timeval tod;
+	struct tm ltime;
+	char date[64];
+
+	if (!debug_display_time)
+		return 0;
+
+	if (gettimeofday(&tod, NULL) != 0)
+		return 0;
+
+	if (localtime_r(&tod.tv_sec, &ltime) == NULL)
+		return 0;
+
+	strftime(date, sizeof(date),  "%F %H:%M:%S", &ltime);
+	return fprintf(file, "[%s.%06lu] ", date, (long)tod.tv_usec);
+}
+
+int veprintf(int level, int var, const char *fmt, va_list args)
+{
+	int ret = 0;
+
+	if (var >= level) {
+		if (use_browser >= 1 && !redirect_to_stderr) {
+			ui_helpline__vshow(fmt, args);
+		} else {
+			ret = fprintf_time(debug_file());
+			ret += vfprintf(debug_file(), fmt, args);
+		}
+	}
+
+	return ret;
+}
+
+int eprintf(int level, int var, const char *fmt, ...)
+{
+	va_list args;
+	int ret;
+
+	va_start(args, fmt);
+	ret = veprintf(level, var, fmt, args);
+	va_end(args);
+
+	return ret;
+}
+
+static int veprintf_time(u64 t, const char *fmt, va_list args)
+{
+	int ret = 0;
+	u64 secs, usecs, nsecs = t;
+
+	secs   = nsecs / NSEC_PER_SEC;
+	nsecs -= secs  * NSEC_PER_SEC;
+	usecs  = nsecs / NSEC_PER_USEC;
+
+	ret = fprintf(debug_file(), "[%13" PRIu64 ".%06" PRIu64 "] ", secs, usecs);
+	ret += vfprintf(debug_file(), fmt, args);
+	return ret;
+}
+
+int eprintf_time(int level, int var, u64 t, const char *fmt, ...)
+{
+	int ret = 0;
+	va_list args;
+
+	if (var >= level) {
+		va_start(args, fmt);
+		ret = veprintf_time(t, fmt, args);
+		va_end(args);
+	}
+
+	return ret;
+}
+
+/*
+ * Overloading libtraceevent standard info print
+ * function, display with -v in perf.
+ */
+void pr_stat(const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	veprintf(1, verbose, fmt, args);
+	va_end(args);
+	eprintf(1, verbose, "\n");
+}
+
+int dump_printf(const char *fmt, ...)
+{
+	va_list args;
+	int ret = 0;
+
+	if (dump_trace) {
+		va_start(args, fmt);
+		ret = vprintf(fmt, args);
+		va_end(args);
+	}
+
+	return ret;
+}
+
+static int trace_event_printer(enum binary_printer_ops op,
+			       unsigned int val, void *extra, FILE *fp)
+{
+	const char *color = PERF_COLOR_BLUE;
+	union perf_event *event = (union perf_event *)extra;
+	unsigned char ch = (unsigned char)val;
+	int printed = 0;
+
+	switch (op) {
+	case BINARY_PRINT_DATA_BEGIN:
+		printed += fprintf(fp, ".");
+		printed += color_fprintf(fp, color, "\n. ... raw event: size %d bytes\n",
+					 event->header.size);
+		break;
+	case BINARY_PRINT_LINE_BEGIN:
+		printed += fprintf(fp, ".");
+		break;
+	case BINARY_PRINT_ADDR:
+		printed += color_fprintf(fp, color, "  %04x: ", val);
+		break;
+	case BINARY_PRINT_NUM_DATA:
+		printed += color_fprintf(fp, color, " %02x", val);
+		break;
+	case BINARY_PRINT_NUM_PAD:
+		printed += color_fprintf(fp, color, "   ");
+		break;
+	case BINARY_PRINT_SEP:
+		printed += color_fprintf(fp, color, "  ");
+		break;
+	case BINARY_PRINT_CHAR_DATA:
+		printed += color_fprintf(fp, color, "%c",
+			      isprint(ch) && isascii(ch) ? ch : '.');
+		break;
+	case BINARY_PRINT_CHAR_PAD:
+		printed += color_fprintf(fp, color, " ");
+		break;
+	case BINARY_PRINT_LINE_END:
+		printed += color_fprintf(fp, color, "\n");
+		break;
+	case BINARY_PRINT_DATA_END:
+		printed += fprintf(fp, "\n");
+		break;
+	default:
+		break;
+	}
+
+	return printed;
+}
+
+void trace_event(union perf_event *event)
+{
+	unsigned char *raw_event = (void *)event;
+
+	if (!dump_trace)
+		return;
+
+	print_binary(raw_event, event->header.size, 16,
+		     trace_event_printer, event);
+}
+
+static struct sublevel_option debug_opts[] = {
+	{ .name = "verbose",		.value_ptr = &verbose },
+	{ .name = "ordered-events",	.value_ptr = &debug_ordered_events},
+	{ .name = "stderr",		.value_ptr = &redirect_to_stderr},
+	{ .name = "data-convert",	.value_ptr = &debug_data_convert },
+	{ .name = "perf-event-open",	.value_ptr = &debug_peo_args },
+	{ .name = "kmaps",		.value_ptr = &debug_kmaps },
+	{ .name = "type-profile",	.value_ptr = &debug_type_profile },
+	{ .name = NULL, }
+};
+
+int perf_debug_option(const char *str)
+{
+	int ret;
+
+	ret = perf_parse_sublevel_options(str, debug_opts);
+	if (ret)
+		return ret;
+
+	/* Allow only verbose value in range (0, 10), otherwise set 0. */
+	verbose = (verbose < 0) || (verbose > 10) ? 0 : verbose;
+
+#if LIBTRACEEVENT_VERSION >= MAKE_LIBTRACEEVENT_VERSION(1, 3, 0)
+	if (verbose == 1)
+		tep_set_loglevel(TEP_LOG_INFO);
+	else if (verbose == 2)
+		tep_set_loglevel(TEP_LOG_DEBUG);
+	else if (verbose >= 3)
+		tep_set_loglevel(TEP_LOG_ALL);
+#endif
+	return 0;
+}
+
+int perf_quiet_option(void)
+{
+	struct sublevel_option *opt = &debug_opts[0];
+
+	/* disable all debug messages */
+	while (opt->name) {
+		*opt->value_ptr = -1;
+		opt++;
+	}
+
+	/* For debug variables that are used as bool types, set to 0. */
+	redirect_to_stderr = 0;
+	debug_peo_args = 0;
+	debug_kmaps = 0;
+	debug_type_profile = 0;
+
+	return 0;
+}
+
+#define DEBUG_WRAPPER(__n, __l)				\
+static int pr_ ## __n ## _wrapper(const char *fmt, ...)	\
+{							\
+	va_list args;					\
+	int ret;					\
+							\
+	va_start(args, fmt);				\
+	ret = veprintf(__l, verbose, fmt, args);	\
+	va_end(args);					\
+	return ret;					\
+}
+
+DEBUG_WRAPPER(warning, 0);
+DEBUG_WRAPPER(debug, 1);
+
+void perf_debug_setup(void)
+{
+	debug_set_file(stderr);
+	libapi_set_print(pr_warning_wrapper, pr_warning_wrapper, pr_debug_wrapper);
+}
+
+void __dump_stack(FILE *file, void **stackdump, size_t stackdump_size)
+{
+	/* TODO: async safety. printf, malloc, etc. aren't safe inside a signal handler. */
+	pid_t pid = getpid();
+	struct machine *machine;
+	struct thread *thread = NULL;
+	struct perf_env host_env;
+
+	perf_env__init(&host_env);
+	machine = machine__new_live(&host_env, /*kernel_maps=*/false, pid);
+
+	if (machine)
+		thread = machine__find_thread(machine, pid, pid);
+
+#ifdef HAVE_BACKTRACE_SUPPORT
+	if (!machine || !thread) {
+		/*
+		 * Backtrace functions are async signal safe. Fall back on them
+		 * if machine/thread creation fails.
+		 */
+		backtrace_symbols_fd(stackdump, stackdump_size, fileno(file));
+		machine__delete(machine);
+		perf_env__exit(&host_env);
+		return;
+	}
+#endif
+
+	for (size_t i = 0; i < stackdump_size; i++) {
+		struct addr_location al;
+		u64 addr = (u64)(uintptr_t)stackdump[i];
+		bool printed = false;
+
+		addr_location__init(&al);
+		if (thread && thread__find_map(thread, PERF_RECORD_MISC_USER, addr, &al)) {
+			al.sym = map__find_symbol(al.map, al.addr);
+			if (al.sym) {
+				fprintf(file, "    #%zd %p in %s ", i, stackdump[i], al.sym->name);
+				printed = true;
+			}
+		}
+		if (!printed)
+			fprintf(file, "    #%zd %p ", i, stackdump[i]);
+
+		map__fprintf_srcline(al.map, al.addr, "", file);
+		fprintf(file, "\n");
+		addr_location__exit(&al);
+	}
+	thread__put(thread);
+	machine__delete(machine);
+	perf_env__exit(&host_env);
+}
+
+/* Obtain a backtrace and print it to stdout. */
+#ifdef HAVE_BACKTRACE_SUPPORT
+void dump_stack(void)
+{
+	void *stackdump[32];
+	size_t size = backtrace(stackdump, ARRAY_SIZE(stackdump));
+
+	__dump_stack(stdout, stackdump, size);
+}
+#else
+void dump_stack(void) {}
+#endif
+
+void sighandler_dump_stack(int sig)
+{
+	psignal(sig, "perf");
+	dump_stack();
+	signal(sig, SIG_DFL);
+	raise(sig);
+}