From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers 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 Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- samples/trace_events/trace-events-sample.c | 157 +++++++++++++++++++++++++++++ 1 file changed, 157 insertions(+) create mode 100644 samples/trace_events/trace-events-sample.c (limited to 'samples/trace_events/trace-events-sample.c') diff --git a/samples/trace_events/trace-events-sample.c b/samples/trace_events/trace-events-sample.c new file mode 100644 index 000000000..0b7a6efdb --- /dev/null +++ b/samples/trace_events/trace-events-sample.c @@ -0,0 +1,157 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include +#include + +/* + * Any file that uses trace points, must include the header. + * But only one file, must include the header by defining + * CREATE_TRACE_POINTS first. This will make the C code that + * creates the handles for the trace points. + */ +#define CREATE_TRACE_POINTS +#include "trace-events-sample.h" + +static const char *random_strings[] = { + "Mother Goose", + "Snoopy", + "Gandalf", + "Frodo", + "One ring to rule them all" +}; + +static void do_simple_thread_func(int cnt, const char *fmt, ...) +{ + unsigned long bitmask[1] = {0xdeadbeefUL}; + va_list va; + int array[6]; + int len = cnt % 5; + int i; + + set_current_state(TASK_INTERRUPTIBLE); + schedule_timeout(HZ); + + for (i = 0; i < len; i++) + array[i] = i + 1; + array[i] = 0; + + va_start(va, fmt); + + /* Silly tracepoints */ + trace_foo_bar("hello", cnt, array, random_strings[len], + current->cpus_ptr, fmt, &va); + + va_end(va); + + trace_foo_with_template_simple("HELLO", cnt); + + trace_foo_bar_with_cond("Some times print", cnt); + + trace_foo_with_template_cond("prints other times", cnt); + + trace_foo_with_template_print("I have to be different", cnt); + + trace_foo_rel_loc("Hello __rel_loc", cnt, bitmask, current->cpus_ptr); +} + +static void simple_thread_func(int cnt) +{ + do_simple_thread_func(cnt, "iter=%d", cnt); +} + +static int simple_thread(void *arg) +{ + int cnt = 0; + + while (!kthread_should_stop()) + simple_thread_func(cnt++); + + return 0; +} + +static struct task_struct *simple_tsk; +static struct task_struct *simple_tsk_fn; + +static void simple_thread_func_fn(int cnt) +{ + set_current_state(TASK_INTERRUPTIBLE); + schedule_timeout(HZ); + + /* More silly tracepoints */ + trace_foo_bar_with_fn("Look at me", cnt); + trace_foo_with_template_fn("Look at me too", cnt); +} + +static int simple_thread_fn(void *arg) +{ + int cnt = 0; + + while (!kthread_should_stop()) + simple_thread_func_fn(cnt++); + + return 0; +} + +static DEFINE_MUTEX(thread_mutex); +static int simple_thread_cnt; + +int foo_bar_reg(void) +{ + mutex_lock(&thread_mutex); + if (simple_thread_cnt++) + goto out; + + pr_info("Starting thread for foo_bar_fn\n"); + /* + * We shouldn't be able to start a trace when the module is + * unloading (there's other locks to prevent that). But + * for consistency sake, we still take the thread_mutex. + */ + simple_tsk_fn = kthread_run(simple_thread_fn, NULL, "event-sample-fn"); + if (IS_ERR_OR_NULL(simple_tsk_fn)) { + pr_err("Failed to create simple_thread_fn\n"); + simple_tsk_fn = NULL; + } + out: + mutex_unlock(&thread_mutex); + return 0; +} + +void foo_bar_unreg(void) +{ + mutex_lock(&thread_mutex); + if (--simple_thread_cnt) + goto out; + + pr_info("Killing thread for foo_bar_fn\n"); + if (simple_tsk_fn) + kthread_stop(simple_tsk_fn); + simple_tsk_fn = NULL; + out: + mutex_unlock(&thread_mutex); +} + +static int __init trace_event_init(void) +{ + simple_tsk = kthread_run(simple_thread, NULL, "event-sample"); + if (IS_ERR(simple_tsk)) + return -1; + + return 0; +} + +static void __exit trace_event_exit(void) +{ + kthread_stop(simple_tsk); + mutex_lock(&thread_mutex); + if (simple_tsk_fn) + kthread_stop(simple_tsk_fn); + simple_tsk_fn = NULL; + mutex_unlock(&thread_mutex); +} + +module_init(trace_event_init); +module_exit(trace_event_exit); + +MODULE_AUTHOR("Steven Rostedt"); +MODULE_DESCRIPTION("trace-events-sample"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1